certain illustrative embodiments of the invention are described below . the present invention is not limited to these embodiments . the compositions of the present invention provide novel chemoprotectants that , when administered to a subject receiving chemo or radiation therapy , selectively protects the subject &# 39 ; s cells and tissues , and not tumor tissues , from toxic therapeutic effects . once activated , compositions of the present invention serve , for example , as a direct precursor to glutathione , a key regulator of apoptosis . the presence of a phosphorothioate moiety , or other protecting moiety , in the compositions as described herein requires cleavage by alkaline phosphatase , present in normal cells but much less so in tumor neovasculature . elevations of glutathione in normal tissues render the patient less susceptible to the toxic effects of chemotherapy and radiation therapy , whereas cancerous cells within a tumor are not so protected . in some embodiments , the compositions as described herein undergo dephosphorylation ( e . g ., by alkaline phosphatase ) in vitro under experimental parameters or in vivo in the normal cells and tissues of a subject . once dephosphorylated , the composition comprises an active free sulfhydryl ( thiol , — sh ) group that protects against the toxicities associated with chemotherapy and radiation therapy by acting as a scavenger for reactive oxygen species created by such therapies ( yuhas , 1977 , in : radiation - drug interactions in cancer management , pp . 303 - 352 ); yuhas , 1973 , j . natl . cancer inst . 50 : 69 - 78 ; incorporated by reference herein in their entireties ). in one embodiment , the present invention relates to protection of non - diseased cells and tissues by administering prior to , during , or after , irradiation and / or chemotherapy to a tumor tissue , a therapeutically effective amount of a composition as described herein . in some embodiments , the administration of a composition of the present invention is directed specifically to the non - diseased cells and tissues , whereas the administration of the chemotherapy and / or irradiation is not so discriminating . in one embodiment , the compositions of the present invention include small molecules , or analogs thereof , of the structure as seen in formula i : r 1 and r 2 are each , separately , hydrogen , methyl , or ethyl ; and in one embodiment , the present invention provides salts , solvates and hydrates of the compounds as described herein . an example of an acceptable salt is found in formula ii : r 1 and r 2 are each , separately , hydrogen , methyl , or ethyl ; and in some embodiments , a further example of a salt composition suitable for use as a composition in the methods of the present application is found in formula iii : in some embodiments , two or more therapeutic molecules of interest are provided in a single therapeutic agent as a single molecule , such that the two or more therapeutic molecules of interest are generated intracellularly . one or more of the constituents may also be selected to increase molecule stability , cell permeability , or other desired properties . for example , in one embodiment , the compositions of the present invention include small molecules , or analogs thereof , of the structure as seen in formula iv : the compound of formula iv is metabolized to provide both glutathione and lipoic acid to a cell , each providing protection against toxic agents or conditions . such a molecule undergoes , for example , cleavage of the thiol protecting phosphate by alkaline phosphatase . it is contemplated that the nonpolar molecule is readily cell permeable . esterase cleavage of the conjugate and liberation of the glutathione molecule and alpha - lipoic acid provide intracellular protection . therapeutic agents can also be provided as dimers or other multimers of protective molecules . for example , in some embodiments , the therapeutic agent comprises a molecule as seen in formula v , a protected dimer of glutathione : in some embodiments , compositions of the present invention are co - administered with chemotherapy and / or anticancer therapy and / or radiation therapy and another chemoprotectant compound ( e . g ., amifostine , mesna ). in some embodiments , the administration of a composition of the present invention is directed specifically to the non - diseased cells and tissues , whereas the administration of the chemotherapy and / or irradiation is not so discriminating . for example , table 1 lists compounds for co - administration with a composition of the present invention . numerous other examples of chemotherapeutic compounds and anticancer therapies suitable for co - administration with the disclosed compositions are known to those skilled in the art . in some embodiments , the compositions of the present invention are especially useful when co - administered with an anti - cancer drug whose cytotoxicity is due primarily to the production of reactive oxygen species , for example , doxorubicin , daunorubicin , mitocyn c , etoposide , cisplatin , arsenic tioxide , ionizing radiation and photodynamic therapy . anticancer agents further include compounds which have been identified to have anticancer activity but are not currently approved by the united states food and drug administration or other counterpart agencies or are undergoing evaluation for new uses . examples include , but are not limited to , 3 - ap , 12 - o - tetradecanoylphorbol - 13 - acetate , 17aag , 852a , abi - 007 , abr - 217620 , abt - 751 , adi - peg 20 , ae - 941 , ag - 013736 , agro100 , alanosine , amg 706 , antineoplastons , ap23573 , apaziquone , apc8015 , atiprimod , atn - 161 , atrasenten , azacitidine , bb - 10901 , bcx - 1777 , bevacizumab , bg00001 , bicalutamide , bms 247550 , bortezomib , bryostatin - 1 , buserelin , calcitriol , cci - 779 , cdb - 2914 , cefixime , cetuximab , cgo070 , cilengitide , clofarabine , combretastatin a4 phosphate , cp - 675 , 206 , cp - 724 , 714 , cpg 7909 , curcumin , decitabine , denspm , doxercalciferol , e7070 , e7389 , ecteinascidin 743 , efaproxiral , eflomithine , ekb - 569 , enzastaurin , erlotinib , exisulind , fenretinide , flavopiridol , fludarabine , flutamide , fotemustine , fr901228 , g17dt , galiximab , gefitinib , genistein , glufosfamide , gti - 2040 , histrelin , hki - 272 , homoharringtonine , hsppc - 96 , iloprost , imiquimod , infliximab , interleukin - 12 , ipi - 504 , irofulven , ixabepilone , lapatinib , lenalidomide , lestaurtinib , leuprolide , lmb - 9 immunotoxin , lonafarnib , luniliximab , mafosfamide , mb07133 , mdx - 010 , mln2704 , monoclonal antibody 3f8 , monoclonal antibody j591 , motexafin , ms - 275 , mva - muc1 - il2 , nilutamide , nitrocamptothecin , nolatrexed dihydrochloride , nolvadex , ns - 9 , 06 - benzylguanine , oblimersen sodium , onyx - 015 , oregovomab , osi - 774 , panitumumab , paraplatin , pd - 0325901 , pemetrexed , phy906 , pioglitazone , pirfenidone , pixantrone , ps - 341 , psc 833 , pxd101 , pyrazoloacridine , r115777 , rad001 , ranpirnase , rebeccamycin analogue , rhuangiostatin protein , rhumab 2c4 , rosiglitazone , rubitecan , s - 1 , s - 8184 , satraplatin , sb -, 15992 , sgn - 0010 , sgn - 40 , sorafenib , sr31747a , st1571 , su011248 , suberoylanilide hydroxamic acid , suramin , talabostat , talampanel , tariquidar , temsirolimus , tgfa - pe38 immunotoxin , thalidomide , thymalfasin , tipifarnib , tirapazamine , tlk286 , trabectedin , trimetrexate glucuronate , trovax , ucn - 1 , valproic acid , vinflunine , vnp40101m , volociximab , vorinostat , vx - 680 , zd1839 , zd6474 , zileuton , and zosuquidar trihydrochloride . for a more detailed description of anticancer agents and other therapeutic agents , those skilled in the art are referred to any number of instructive manuals including , but not limited to , the physician &# 39 ; s desk reference , goodman and gilman &# 39 ; s “ pharmaceutical basis of therapeutics ” 10th edition , eds . hardman et al ., 2002 and later editions , and “ biologic therapy of cancer , 2nd edition , eds . devita et al ., 1995 , jb lippincott co . publ , p . 919 and later editions , incorporated herein by reference in their entireties . in some embodiments , gsh levels in cells , for example both normal and tumor cells , are reduced prior to the administration of compounds of formula i , ii , or iii . by lowering gsh levels in all cells , cancer cells become vulnerable to therapies . however , following treatment with formula i , ii , or iii , normal cells are made substantially more resistant to the toxic effects of the cancer therapies . thus , in these embodiments , cancer cells are supersensitized to therapy , while normal cells are protected . the present invention is not limited by the nature of the compound or treatment used to reduce gsh levels . in one embodiment , the present invention provides for the use and administration of 2 - amino - 4 -( s - butylsulfonimidoyl ) butanoic acid ( buthionine sulfoximine or bso ) in conjunction with the compositions of the present invention . in some embodiments , buthionine sulfoximine inhibits the synthesis of gsh in both non - tumor and tumor cells by inhibiting γ - glutamulcysteine synthetase , an essential enzyme for synthesis of gsh , and a composition of the present invention replenishes gsh in non - tumor cells . in some embodiments , bso is administered prior to the administration of a composition of the present invention . in some embodiments , bso is administered in conjunction with a compositions of the present invention . in some embodiments , the bso and a composition of the present invention are administered prior to , at the same time , or after the administration of chemotherapeutics and / or radiotherapy to a subject . it is contemplated that as bso decreases the amount of gsh in tumor and non - tumor cells , the addition of a composition of the present invention replenishes gsh in non - tumor cells but not tumor cells , as such the tumor cells maintain low or non - existent gsh levels throughout the administration of chemotherapeutic drugs and / or radiotherapy . the low or non - existent levels of gsh in tumor cells following administration of bso strips them of the protective effects that gsh offers tumor cells , thereby allowing for more efficient targeting and eradication of the tumor cells by chemo and radiation therapies . in some embodiments , the administration of bso and a compound of the present invention allows for the administration of lesser amounts ( potentially for longer time periods ) of chemotherapeutic drugs than normal due to the low or non - existent levels of gsh in tumor cells , and at the same time the non - tumor cells of a subject are less exposed to the toxic effects of the therapy . in some embodiments , the compositions of the present invention are useful in preparation as adjuvants to chemo and / or anticancer therapy and radiation therapy . the methods and techniques for preparing medicaments comprising a composition of the present invention are well - known in the art . exemplary pharmaceutical formulations and routes of delivery are described below . one of skill in the art will appreciate that any one or more of the compounds described herein , including the many specific embodiments , are prepared by applying standard pharmaceutical manufacturing procedures . such medicaments can be delivered to the subject by using delivery methods that are well - known in the pharmaceutical arts . in some embodiments of the present invention , the compositions are administered alone , while in some other embodiments , the compositions are preferably present in a pharmaceutical formulation comprising at least one active ingredient / agent , as defined above , together with one or more pharmaceutically acceptable carriers and optionally other therapeutic agents . each carrier should be “ acceptable ” in the sense that it is compatible with the other ingredients of the formulation and not injurious to the subject . formulations include , for example , parenteral administration ( e . g ., subcutaneous , intramuscular , intravenous , intradermal ) and site - specific administration . in some embodiments , formulations are conveniently presented in unit dosage form and are prepared by any method known in the art of pharmacy . such methods include the step of bringing into association the active ingredient with the carrier that constitutes one or more accessory ingredients . in general , the formulations are prepared by uniformly and intimately bringing into association ( e . g ., mixing ) the active ingredient with liquid carriers or finely divided solid carriers or both , and then if necessary shaping the product . formulations suitable for parenteral administration include aqueous and non - aqueous isotonic sterile injection solutions which may contain antioxidants , buffers , bacteriostats and solutes which render the formulation isotonic with the blood of the intended recipient ; and aqueous and non - aqueous sterile suspensions which may include suspending agents and thickening agents , and liposomes or other microparticulate systems which are designed to target the compound to blood components or one or more organs . in some embodiments , the formulations are presented / formulated in unit - dose or multi - dose sealed containers , for example , ampoules and vials , and may be stored in a freeze - dried ( lyophilized ) condition requiring only the addition of the sterile liquid carrier , for example water for injections , immediately prior to use . extemporaneous injection solutions and suspensions may be prepared from sterile powders , granules and tablets of the kind previously described . it should be understood that in addition to the ingredients particularly mentioned above , the formulations of this invention may include other agents conventional in the art having regard to the type of formulation in question , for example , those suitable for oral administration may include such further agents as sweeteners , thickeners and flavoring agents . it also is intended that the agents , compositions and methods of this invention be combined with other suitable compositions and therapies . various delivery systems are known and can be used to administer compositions of the present invention . methods of delivery include , but are not limited to , intra - arterial , intra - muscular , intravenous , and site specific . for example , in some embodiments , it may be desirable to administer the compositions of the invention locally to the area targeted by chemo and / or anticancer therapies and / or radiation therapy ; this may be achieved by , for example , and not by way of limitation , local infusion during surgery , injection , or by means of a catheter . in some embodiments , in vivo administration of the compositions as described herein is effected in one dose , continuously or intermittently throughout the course of treatment . methods of determining the most effective means and dosage of administration are well known to those of skill in the art and vary with , for example , the composition used for therapy , the target cell being treated and the subject being treated . single or multiple administrations are carried out with the dose level and pattern being selected by the treating physician . in some embodiments , the compositions as described herein are delivered to the subject prior to administration of the chemotherapeutic agent . in some embodiments , compositions as described herein are delivered on a daily basis ( e . g ., at least once , at least twice , at least three times ) and accompany the administration of radiotherapy . suitable dosage formulations and methods of administering the agents are readily determined by those of skill in the art . when the compositions described herein are co - administered with another chemoprotective agent , the effective amount may be less than when the agent is used alone . ideally , the agent should be administered to achieve peak concentrations of the active compound at the target sites for chemo and radiation therapy . desirable blood levels of the agent may be maintained by a continuous infusion to provide a therapeutic amount of the active ingredient within the target tissue . the present invention also includes methods involving co - administration of the compositions described herein with one or more additional active agents . indeed , it is a further aspect of this invention to provide methods for enhancing prior art therapies and / or pharmaceutical compositions by co - administering a compound of this invention . in co - administration procedures , the agents may be administered concurrently or sequentially . in one embodiment , the compounds described herein are administered prior to the other active agent ( s ). the pharmaceutical formulations and modes of administration may be any of those described above . in addition , the two or more co - administered chemical agents , biological agents or radiation may each be administered using different modes or different formulations . the agent or agents to be co - administered depends on the type of condition being treated . for example , when treating cancer , the additional agent is a chemotherapeutic agent , anticancer agent , or radiation . the additional agents to be co - administered , such as anticance can be any of the well - known agents in the art , including , but not limited to , those that are currently in clinical use ( see table i for exemplary agents ). the determination of appropriate type and dosage of radiation treatment is also within the skill in the art or can be determined with relative ease . treatment of the various conditions associated with abnormal apoptosis is generally limited by the following two major factors : ( 1 ) the development of drug resistance and ( 2 ) the toxicity of known therapeutic agents . in certain cancers , for example , resistance to chemicals and radiation therapy has been shown to be associated with inhibition of apoptosis . some therapeutic agents have deleterious side effects , including non - specific lymphotoxicity , renal and bone marrow toxicity . the compositions and methods described herein address both these problems . drug resistance , where increasing dosages are required to achieve therapeutic benefit , is overcome by co - administering the compositions described herein with the known agent . the compositions described herein protect cells and tissues from toxic effects of chemotherapeutic drugs and radiation therapy and , accordingly , less of these agents are needed to achieve a therapeutic benefit . conversely , the protection of normal cells and tissues against the toxic effects of anticancer therapies by co - administration of the compositions as described herein allows for higher doses and / or longer treatment regimens when using such therapies , thereby providing the medical practitioner with the tools to follow a more aggressive anticancer strategy than was otherwise deemed possible . in some embodiments , the present invention provides methods for using the compositions as described herein for screening for the efficacy of such compositions in inhibiting or decreasing toxicity in cells and tissues when such cells and tissues are administered cancer , or other , therapies that are toxic to normal cells . in some embodiments , methods for screening are conducted in vitro . in other embodiments , these screens are conducted in vivo . in some embodiments , methods of the present invention are performed in vivo in non - human animals or human subjects . in some embodiments , the methods screen for the inhibition or decrease of apoptosis is cells , in vitro or in vivo , when such cells , non - human animals , or human subjects are co - administered a cancer , or other , therapy in combination with compositions of the present invention . in some embodiments , such methods define efficacy of the compositions as described herein for use in decreasing or inhibiting the toxic effects of therapies by comparing results from a screen with a composition of the present invention to a screen performed without said composition ( e . g ., control experiment ). toxic effects of therapies on cells includes cellular death by apoptosis as a result of the therapy . a composition of the present invention that is efficacious in inhibiting or decreasing the toxic effects of therapies is one that inhibits or decreases cellular apoptosis in normal , non - diseased cells when toxic therapies are administered . a skilled artisan will understand methods for determining cellular apoptosis . these methods include , but are not limited to , measuring apoptotic indicator enzymes such as caspase 3 / 7 , 8 or 9 , tdt - mediated dutp nick - end labeling ( tunel ) assays , and apoptosis related antibodies ( e . g ., anti - parp , anti - caspase 3 , etc .). detection methods utilized with apoptotic assays include fluorometric , luminescent , and calorimetric . in some embodiments , such in vivo uses are , for example , performed by taking a subject ( e . g ., human or non - human animal ) with cancer and co - administering a therapy regimen in conjunction with a composition of the present invention , and comparing the outcome of such an administration with a subject that received the same therapy regimen without co - administration of a composition of the present invention . in some embodiments , such in vitro uses are , for example , performed in tissue culture dishes with primary or immortalized tissue culture cells ( e . g ., hela , hek293 , cho , 3t3 , etc .) or tissue explants . in such in vitro uses , a composition of the present invention is co - administered with a therapy regimen known to be toxic to normal cells , the results being compared with results from tissue culture cells or explants that receive the same therapy regimen without a composition of the present invention . the following examples are provided in order to demonstrate and further illustrate certain preferred embodiments and aspects of the present invention and are not to be construed as limiting the scope thereof . in the experimental disclosure which follows , the following abbreviations apply : equiv ( equivalents ); m ( molar ); n ( normal ); mol ( moles ); mmol ( millimoles ); g ( grams ); l ( liters ); ml ( milliliters ); 0 ° c . ( degrees centigrade ); min . ( minutes ); % ( percent ); psi ( pounds per square inch ). glutamine ( 36 . 5 g , 0 . 25 mol ) was stirred with 1m sodium bicarbonate ( 750 ml ) and toluene ( 200 ml ). benzyl chloroformate ( 50 ml , 59 . 75 g , 0 . 35 mol , 1 . 4 equiv .) was added drop - wise over 20 min . and the resulting mixture was stirred under nitrogen at room temperature overnight . ethyl acetate ( 400 ml ) was added and phases were separated . the organic phase was extracted with water ( 50 ml ) and discarded . the aqueous phase was acidified with 6n hydrochloric acid and extracted with ethyl acetate ( 2 × 600 ml ). the combined extracts were washed with water ( 100 ml ) and stripped . the residue was dried in a vacuum oven ( 50 ° c .) to produce ( 1 ) ( 64 g , 91 . 4 %). a mixture of acid ( 1 ) ( 64 g , 0 . 228 mol ), dimeththylformamide ( 210 ml ) and sodium bicarbonate ( 111 g , 1 . 32 mol , 5 . 8 equiv .) was stirred at room temperature for 30 min . ethyl iodide ( 34 ml , 66 . 3 g , 0 . 425 mol , 1 . 86 equiv .) was added and stirring was continued overnight under nitrogen . the reaction mixture was slowly diluted with water to 1 l and stirred for 40 min . the solid was collected by filtration , washed well with water and partitioned between ethyl acetate ( 8 l ) and water ( 3 l ). phases were separated and the aqueous phase was extracted with ethyl acetate ( 2 . 5 l ). the combined organic extracts were washed with water ( 1 l ), dried over sodium sulfate , stripped and dried in a vacuum oven ( 50 ° c .) to produce ( 2 ) ( 47 g , 66 . 7 %). a suspension of the amide ( 2 ) ( 38 g , 0 . 1233 mol ) in anhydrous acetonitrile ( 400 ml ) was stirred at reflux under nitrogen and t - butyl nitrite ( 35 ml , 3 . 17 equiv .) was added quickly . the reflux was continued for 2 hrs . after cooling , the solvent was removed in a rotary evaporator . the residue was taken in water ( 250 ml ) and ethyl acetate ( 500 ml ) and the biphasic mixture was stirred well while solid sodium bicarbonate was slowly added to ph = 7 . 5 . phases were separated and the organic phase was washed with 10 % sodium bicarbonate ( 200 ml ). the combined aqueous extracts were washed with ethyl acetate ( 300 ml ), made acidic with 6n hydrochloric acid and extracted with ethyl acetate ( 2 × 300 ml ). the combined extracts were washed with water ( 150 ml ), dried over sodium sulfate , stripped and the residue was dried in a vacuum oven ( 50 ° c .) to produce ( 3 ) ( 24 . 6 g , 64 . 7 %). a suspension of acid ( 3 ) ( 7 . 6 g , 24 . 57 mmol ) in dry acetonitrile ( 80 ml ) was stirred under nitrogen at room temperature and hobt ( 4 g , 29 . 6 mmol , 1 . 2 equiv .) was added . stirring was continued for 10 min ., and edci ( 5 . 1 g , 26 . 6 mmol , 1 . 1 equiv .) was added . the resulting mixture was stirred for 1 . 5 hrs and serine ethyl ester free base ( 3 . 27 g , 24 . 57 mmol , 1 equiv .) in acetonitrile ( 20 ml ) was added . stirring was continued at room temperature for 3 hrs . the solvent was removed in a rotary evaporator , the residue was partitioned between water ( 100 ml ) and ethyl acetate ( 200 ml ) and phases were separated . the organic phase was washed successively with water ( 50 ml ), 5 % potassium carbonate ( 2 × 50 ml ) and water ( 2 × 50 ml ), dried over sodium sulfate and the solvent removed in a rotary evaporator . the residue was dried in a vacuum oven ( 50 ° c .) to produce ( 4 ) ( 12 . 4 g , 85 . 5 %). a solution of ( 4 ) ( 11 . 4 g , 26 . 86 mmol ) in ethanol ( 225 ml ) containing 1 . 2 g 20 % palladium on activated carbon ( 50 % wet ) was hydrogenated at 30 psi for 3 hrs . the catalyst was removed by filtration and the solution was washed with ethanol . the solvent was removed in a rotary evaporator . the residue was dried in a vacuum oven ( 50 ° c .) to produce ( 5 ) ( 5 . 86 g , 75 %). a solution of alcohol ( 5 ) ( 0 . 29 g , 1 mmol ) in dichloromethane ( 10 ml ) was treated with thionyl chloride ( 1 g ) and stirred at room temperature under nitrogen overnight . the solvent was removed on a rotary evaporator ( bath temperature below 28 ° c .). dichloromethane ( 10 ml ) was added and stripped under the same conditions twice . the solid residue was taken in water ( 8 ml ) and washed with mtbe ( 2 × 15 ml ). the resulting aqueous solution contains pure ( 6 ) ( lcms ) and was used as such in the next step . a solution of trisodium thiophosphate ( 0 . 4 g ) in water ( 6 ml ) was stirred at room temperature under nitrogen and the solution of ( 6 ) prepared above was added all at once . the reaction mixture was stirred at room temperature under nitrogen overnight . the ph was carefully adjusted to 8 . 0 with acetic acid and the resulting solution was run through a reverse phase column ( p18 ) using water as the eluent . fractions were checked by lcms and those containing the product were evaporated to dryness ( oil pump vacuum , bath temperature below 25 ° c .) to produce 47 mg of ( 7 ). lcms ( m = 386 ), 1 h nmr and 31 p nmr were used to confirm the final structure ( 7 ). assays were performed to verify the ability of alkaline phosphatase to dephosphorylate compound ( 7 ) to create sulfhydryl reactive groups . calf intestinal alkaline phosphatase ( ciap , sigma ) was diluted in phosphate buffered saline ( pbs ) to 250 units / ml , and frozen in tubes containing 100 μl aliquots . the following solutions were prepared ; 2 mm glutathione ( gsh ), 1 . 05 mm dtnb ( 5 - 5 ′- dithio - bis -( 2 - nitrobenzoic acid ; also known as ellman &# 39 ; s reagent ) and 5 mm amifostine ( af ; 1 mg / ml ). alkaline phosphatase activity , and the ability of the assay to measure reactive sulfhydryl groups in solution , were evaluated initially using amifostine as the control composition . absorbances were measured at a 412 . an increase in absorbance is indicative of free reactive sulfhydryl groups present in the reaction . reaction conditions and results are found in table 2 ; volumes are in μls , reaction 1 was incubated for 5 min . at room temperature prior to absorbance reading , and reactions 2 - 5 were incubated for 10 min . at room temperature prior to absorbance readings . as seen in table 2 , the positive control ( reaction 1 ) and the test reaction 5 ( with amifostine ) have similar absorbance readings , indicating that the reaction conditions are capable of measuring free sulfhydryl groups after dephosphorylation of a compound with alkaline phosphatase ( reaction 5 ). a second assay was performed to examine the ability of alkaline phosphatase to dephosphorylate compound ( 7 ) to create sulfhydryl reactive groups . a 12 . 5 mm solution of compound 7 was made ( 4 mg / ml ) and used in the test reactions . reaction conditions and results are found in table 3 ; volumes are in μls , reactions were incubated for 10 min . at 37 ° c . prior to absorbance readings , duplicates of the compound 7 ( c7 ) negative reaction ( without ciap ; reactions 6 & amp ; 8 ) and compound 7 test reaction ( with ciap ; reactions 7 & amp ; 9 ) were performed . as seen in table 3 , compound 7 is dephosphorylated by alkaline phosphatase to yield free reactive sulfhydryl groups . such reactive sulfhydryl groups are capable of capturing free oxygen radicals created by chemotherapy and / or radiation therapy , thereby inhibiting or decreasing toxicity of these compounds to normal cells and tissues . a time course of dephosphorylation was also performed using compound 7 , following the same reaction conditions as in table 3 . the time course showed that over a 30 min . period ( a 412 readings taken at 3 min . intervals ) the dephosphorylation of compound 7 was time dependent , as an increase in free sulfhydryl groups was seen over time . the compound ( 2 - amino - 4 -( 1 - ethoxycarbonyl - 2 - phosphonosulfanyl - ethylcarbamoyl )- butyric acid ethyl ester monosodium salt ) was tested for intracellular properties . in particular , experiments were conducted to determine the ability of the compound to enter into cells and generate glutathione . hepg2 were incubated with the compound with or without added bovine intestinal alkaline phosphatase ( sigma ). cells were scraped into ssa , vortexed and then spun . gsh in the supernatants were analyzed utilizing the glutathione reductase method of tietze ( tietze f : “ enzymic method for quantitative determination of nanogram amounts of total and oxidized glutathione applications to mammalian blood and other tissues ” analytical biochemistry , 27 ( 3 ): 502 - 522 ( 1969 )). the compound did not enter cells unless the phosphate group was first hydrolyzed with alkaline phosphatase . cells treated with the compound and alkaline phosphatase had a 3 . 6 fold increase in their gsh contents . importantly , this increase in cellular gsh levels also occurred in the presence of buthionine sulfoximine ( greater than 5 fold increase in cellular gsh ), indicating that the compound was not simply delivering cysteine or other building blocks for gsh synthesis but rather delivering gamma - glutamyl cysteine . cells incubated with compound with or without alkaline phosphatase did not exhibit any evidence of toxicity . in experiments with mice and hamsters , no overt toxicity was observed , with testing conducted at doses up to 5 mmoles / animal . the following example provides a protocol for generating gram quantities of 2 - amino - 4 -( 1 - ethoxycarbonyl - 2 - phosphonosulfanyl - ethylcarbamoyl )- butyric acid ethyl ester monosodium salt . l - glutamine ( 500 g , 3 . 42 mol ) was stirred with 1m sodium bicarbonate ( 10 . 26 l ) and toluene ( 2 . 75 l ). benzyl chloroformate ( 684 ml , 818 g , 4 . 8 mol , 1 . 4 equiv .) was added dropwise over 60 min . and the resulting mixture was stirred under nitrogen at room temperature overnight . ethyl acetate ( 6 l ) was added , phases were separated . the organic phase was extracted with water ( 1 l ) and discarded . the aqueous phase was made acidic with 6n hydrochloric acid ( 11 . 6 l ) and extracted with ethyl acetate ( 3 × 6 l ). the combined extracts were washed with water ( 2 l ), brine ( 2 l ) and dried over sodium sulfate . after filtration , the filtrate was concentrated in vacuo to give a residue which was triturated with mtbe . the solid was filtered and was dried in a vacuum oven ( 45 ° c .) to yield ( 823 . 4 g , 86 %) of a solid . ms ( esp ): 303 . 0 ( m + na + ) for c 13 h 16 n 2 o 5 a mixture ( s )- 5 - amino - 2 -( benzyloxycarbonylamino )- 5 - oxopentanoic acid of ( 823 g , 2 . 94 mol ), dimethylformamide ( 3 l ) and sodium bicarbonate ( 1 . 481 kg , 17 . 6 mol , 6 equiv .) was stirred at room temperature for 60 min . ethyl iodide ( 447 ml , 871 g , 5 . 6 mol , 1 . 9 equiv .) was added dropwise over 60 min . and stirring was continued for 4 days under nitrogen . the reaction mixture was slowly diluted with water ( 10 l ) and stirred for 60 min . the solid was collected by filtration , washed with water ( 8 l ) and dried in a convection oven ( 50 ° c .) for 4 days to yield ( 905 g , 100 %) of a solid . ms ( esp ): 331 . 2 ( m + na + ) for c 15 h 20 n 2 o 5 a suspension of the ( s )- ethyl 5 - amino - 2 -( benzyloxycarbonylamino )- 5 - oxopentanoate ( 570 g , 1 . 85 mol ) in anhydrous acetonitrile ( 6 l ) was stirred at reflux under nitrogen and t - butyl nitrite ( 650 ml , 3 . 0 equiv .) was added quickly . the reflux was continued for 2 hrs . after cooling , the solvent was removed in a rotary evaporator . the residue was taken in water ( 1 . 5 l ) and ethyl acetate ( 3 l ) and the biphasic mixture was stirred well while solid sodium bicarbonate was slowly added to ph = 7 . 5 . phases were separated and the organic phase was washed with 10 % sodium bicarbonate ( 6 × 500 ml ). the combined aqueous extracts were washed with ethyl acetate ( 1 l ), made acidic with 6n hydrochloric acid and extracted with ethyl acetate ( 4 × 750 ml ). the combined extracts were dried over sodium sulfate and concentrated in vacuo to yield ( 398 g , 70 %) of a solid . ms ( esp ): 332 . 0 ( m + na + ) for c 15 h 19 no 6 a suspension of ( s )- 4 -( benzyloxycarbonylamino )- 5 - ethoxy - 5 - oxopentanoic acid ( 398 g , 1 . 29 mol ) in dry acetonitrile ( 4 l ) was stirred under nitrogen at room temperature and hobt ( 209 g , 1 . 54 mol , 1 . 2 equiv .) was added . stirring was continued for 10 min , then edci ( 220 g , 1 . 42 mol , 1 . 1 equiv .) was added . the resulting mixture was stirred for 1 . 5 hrs when serine ethyl ester free base ( 171 g , 1 . 29 mol , 1 equiv .) in acetonitrile ( 1 l ) was added . stirring was continued at room temperature for 16 hrs . the solvent was removed in vacuo and the residue was partitioned between water ( 4 l ) and ethyl acetate ( 8 l ) and phases were separated . the organic phase was washed successively with 5 % potassium carbonate ( 2 × 2 l ) and brine ( 2 × 2 l ), dried over sodium sulfate and the solvent was removed in vacuo . the residue was triturated with mtbe , filtered and dried in a vacuum oven ( 45 ° c .) to yield ( 381 . 4 g , 70 %) as a solid . ms ( esp ): 447 . 0 ( m + na + ) for c 20 h 28 n 2 o 8 a solution of ( s )- ethyl 2 -( benzyloxycarbonylamino )- 5 -(( s )- 1 - ethoxy - 3 - hydroxy - 1 - oxopropan - 2 - ylamino )- 5 - oxopentanoate ( 381 g , 0 . 90 mol ) in ethanol ( 7 . 5 l ) containing 76 g of 10 % palladium on activated carbon ( 50 % water wet ) was hydrogenated at 30 psi for 3 hrs . the catalyst was removed by filtration washing the cake with ethanol ( 4 × 2 l ). the solvent was removed in vacuo and the residue was triturated with mtbe ( 2 l ), filtered and dried in a vacuum oven ( 45 ° c .) to yield ( 235 . 3 g , 91 %) of a tan solid . ms ( esp ): 313 . 2 ( m + na + ) for c 12 h 22 n 2 o 6 a solution of ( s )- ethyl 2 - amino - 5 -(( s )- 1 - ethoxy - 3 - hydroxy - 1 - oxopropan - 2 - ylamino )- 5 - oxopentanoate ( 10 g , 35 mmol ) in dichloromethane ( 350 ml ) was treated with thionyl chloride ( 20 ml ) and stirred at room temperature under nitrogen overnight . the solvent was removed on a rotary evaporator ( bath temperature below 28 ° c .). dichloromethane ( 100 ml ) was added and stripped under the same conditions twice . the solid residue was triturated with dcm ( 100 ml ), heptane ( 100 ml ), and mtbe ( 100 ml ), filtered and dried in a vacuum oven ( 25 ° c .) to yield ( 10 g , 84 %) of an off - white solid . ms ( esp ): 309 . 0 ( m + h + ) for c 12 h 21 cln 2 o 5 to solution of 40 g of sodium hydroxide in 300 ml of water was added thiophosphoryl chloride ( 28 . 6 g , 0 . 17 mol ) in one portion and the resulting biphasic solution is quickly heated to reflux . the reaction mixture is heated at reflux until the thiophosphoryl chloride layer is no longer observed ( approx . 30 min .). the heating mantle was removed and the reaction mixture cooled to room temperature . an ice water bath is used to precipitate out the product and sodium salts ( approx . 30 minutes at 0 ° c .). the mixture of product and sodium chloride are filtered off , the solids are collected and dissolved in 150 ml of 45 ° c . water ( removes sodium chloride ). anhydrous methanol ( 200 ml ) is added to precipitate the product which is filtered , collected and stirred under 200 ml of anhydrous methanol for 16 hours to effectively dehydrate the salt . the solids are again collected by filtration and dried in a vacuum oven with no heat for 32 hours to yield ( 17 . 3 g , 56 . 5 %) of a white solid . to a 500 ml round bottom flask was added 250 ml diuf water . water was then degassed with nitrogen over 20 min . ( s )- 5 -(( r )- 3 - chloro - 1 - ethoxy - 1 - oxopropan - 2 - ylamino )- 1 - ethoxy - 1 , 5 - dioxopentan - 2 - aminium chloride ( 5 g , 14 . 5 mmol ) and freshly prepared trisodiumthiophosphate ( 2 . 9 g , 16 . 0 mmol ) were added at once . the reaction mixture was stirred at room temperature under nitrogen for 3 days . the aqueous mixture was concentrated to a minimal volume in vacuo keeping the bath temperature below 25 ° c . the aqueous residue ( 50 ml / run ) was loaded onto an analogix 300 g flash c18 column using water as the eluent to yield ( 6 . 0 g ) of a light yellow foamy solid that is very hygroscopic . ms ( esp ): 387 . 2 ( m + h + ) for c 12 h 23 n 2 o 8 ps 1 h nmr : 1 . 16 ( overlapping triplets , 6h ), 2 . 00 - 2 . 21 ( m , 3h ), 2 . 31 - 2 . 43 ( m , 2h ), 3 . 01 - 3 . 05 ( m , 2h ), 3 . 63 - 4 . 20 ( m , 7h ), 4 . 41 - 4 . 43 ( m , 1h ); 31 p nmr : 17 . 35 ( d ) in some embodiments , the following steps are used for producing compound 7 from compound 5 . synthesis of 3 -( 2 - chloro - 1 - ethoxycarbonyl - ethylcarbamoyl )- 1 - ethoxycarbonyl - propyl - ammonium chloride ( 6 ): a solution of alcohol 5 ( 10 g , 35 mmol ) in dichloromethane ( 350 ml ) was treated with thionyl chloride ( 20 ml ) and stirred at room temperature under nitrogen overnight . the solvent was removed on a rotary evaporator ( bath temperature below 28 ° c .). dichloromethane ( 100 ml ) was added and stripped under the same conditions twice . the solid residue was triturated with dcm ( 100 ml ), heptane ( 100 ml ), and mtbe ( 100 ml ) to give 10 g ( 84 % yield ) of pure 6 ( lcms ) as a off - white solid . synthesis of trisodiumthiophosphate : to a flask was charged 40 g ( 1 . 0 mol ) of sodium hydroxide in 300 ml of water . the solution is stirred until all of the base is dissolved . thiophosphoryl chloride ( 28 . 6 g , 0 . 17 mol ) is added in one portion and the resulting bi - phasic solution is quickly heated to reflux . the reaction mixture is heated at reflux until the thiophosphoryl chloride layer is no longer observed ( approx . 30 min ). the heating mantle is removed and the reaction mixture cooled to room temperature . an ice water bath is used to precipitate out the product and sodium salts ( approx . 30 minutes at 0 ° c .). the mixture of product and sodium chloride is filtered off , the solids are collected and dissolved in 150 ml of 45 ° c . water ( removes sodium chloride ). anhydrous methanol ( 200 ml ) is added to precipitate out the trisodiumphosphoryl chloride . the product is filtered , collected and stirred under 200 ml of anhydrous methanol for 16 hours to effectively dehydrate the salt . the solids are again collected by filtration and dried in a vacuum oven with no heat for 32 hours . 17 . 3 g of product is obtained in 56 . 5 % yield . synthesis of 2 - amino - 4 -( 1 - ethoxycarbonyl - 2 - phosphonosulfanyl - ethylcarbamoyl )- butyric acid ethyl ester monosodium salt ( 7 ): to a 500 ml round bottom flask was added 250 ml diuf water . water was then degassed by nitrogen over 20 min . 5 g 6 and 2 . 9 g fresh made trisodiumthiophosphate were added at once . the reaction mixture was stirred at room temperature under nitrogen for 3 days . lc / ms indicated that the major peak is product . analogix 300 g flash c18 column was then applied to purify the final product to give 6 . 0 g light yellow clear film . all publications and patents mentioned in the present application are herein incorporated by reference . various modification and variation of the described methods and compositions of the invention will be apparent to those skilled in the art without departing from the scope and spirit of the invention . although the invention has been described in connection with specific preferred embodiments , it should be understood that the invention as claimed should not be unduly limited to such specific embodiments . indeed , various modifications of the described modes for carrying out the invention that are obvious to those skilled in the relevant fields are intended to be within the scope of the following claims .
the present invention provides compositions and methods for protecting cells and tissues from damage associated with therapeutic treatments of cancers and other diseases and conditions where reactive oxygen species are produced . the present invention also provides compositions useful as research reagents .