the complexing agents employed in this invention are derivatives of well - known polyaminocarboxylic acid chelating agents , such as dtpa and ethylenediaminetetraacetic acid (&# 34 ; edta &# 34 ;) and cyclic polyaminocarboxylic acid chelating agents such as 1 , 4 , 7 , 10 - tetraazacyclododecane n , n &# 39 ;, n &# 34 ;, n &# 39 ;&# 34 ;- tetra acetic acid (&# 34 ; dota &# 34 ;). in one class of these derivatives , free carboxylic acid groups of the chelating agent ( those not involved in bond formation with the paramagnetic ion ) are converted to aminoalkylamide groups of the formula : ## str12 ## for example , if the polyaminocarboxylic acid chelating agent is dtpa , and the paramagnetic ion is trivalent , two of the carboxylic acid groups will be derivatized to the aminoalkylamide form . likewise , if the paramagnetic ion is divalent , three of the carboxylic acid groups of dtpa or two of the carboxylic acid groups of edta will be derivatized to the aminoalkylamide form . when these complexing agents are reacted with a divalent or trivalent paramagnetic ion , the resulting complexes are substantially non - ionic as evidenced by very low electrical conductivity . examples of types of aminoalkylamide derivatives useful as complexes include those wherein the aminoalkylamide group is ## str13 ## wherein x is o , s or n , unsubstituted or substituted . in a preferred embodiment , the aminoalkylamide group is a morpholinoalkylamide . an alternative class of compounds encompassed by this invention , includes cyclic polyamino carboxylic acid chelating agents , such as dota and trita and represented by the general formula : ## str14 ## in these agents , free carboxylic acid groups are converted to ## str15 ## wherein r 2 &# 39 ; is either ( ch 2 ch 2 o ) p -- r 3 &# 39 ; or ## str16 ## as with the first class of agents described above , if the paramagnetic ion is trivalent , one of the carboxylic acid groups will be derivatized to the aminoalkylamide form , and if the paramagnetic ion is divalent , two of the carboxylic acid groups will be derivatized . examples of types of derivatives useful as complexes include those wherein the amino alkylamide group is : ## str17 ## the aminoalkylamide derivatives of the chelating agents may be prepared by conventional amide - forming reactions . in general , they are prepared by reacting a stoichiometric amount of an aminoalkylamine with a reactive derivative of the polyaminocarboxylic acid chelating agent or cyclic polyaminocarboxylic acid chelating agent under amide - forming conditions . such reactive derivatives include , for example , anhydrides , mixed anhydrides and acid chlorides . to make complexing agents represented by formula i above , the aminoalkylamine has the general formula : ## str18 ## to make complexing agents represented by formula ii above , the aminoalkylamide has the general formula : ## str19 ## in one embodiment for making any of these complexing agents , the reactions are conducted in an organic solvent at an elevated temperature . suitable solvents include those in which the reactants are sufficiently soluble and which are substantially unreactive with the reactants and products . lower aliphatic ketones , ethers , esters , chlorinated hydrocarbons , benzene , toluene , xylene , lower aliphatic hydrocarbons , some lower aliphatic alcohols and the like may advantageously be used as reaction solvents . examples of such solvents are isopropanol , acetone , methylethyl ketone , diethylketone , methyl acetate , ethyl acetate , chloroform , methylene chloride , dichloroethane , hexane , heptane , octane , decane , and the like . if an acid chloride derivative of the polyaminocarboxylic acid is used as the starting material , then the reaction solvent advantageously is one which does not contain reactive functional groups , such as hydroxyl groups , as these solvents can react with the acid chlorides , thus producing unwanted by - products . the reaction temperature may vary widely , depending upon the starting materials employed , the nature of the reaction solvent and other reaction conditions . such reaction temperatures may range , for example , from about 25 ° c . to about 80 ° c ., preferably from about 25 ° c . to about 50 ° c . following reaction of the reactive polyaminocarboxylic acid derivative with the aminoalkylamide , any remaining anhydride or acid chloride groups can be hydrolyzed to the carboxylate groups by adding a stoichiometric excess of water to the reaction mixture and heating for a short time . the resulting aminoalkylamide compound is recovered from the reaction mixture by conventional procedures . for example , the product may be precipitated by adding a precipitating solvent to the reaction mixture , and recovered by filtration or centrifugation . the paramagnetic ion is combined with the aminoalkylamide compound under complex - forming conditions . in general , any of the paramagnetic ions referred to above can be employed in making the complexes of this invention . the complexes can conveniently be prepared by mixing a suitable oxide or salt of the paramagnetic ion with the complexing agent in aqueous solution . to assure complete complex formation , a slight stoichiometric excess of the complexing agent may be used . in addition , an elevated temperature , e . g ., ranging from about 20 ° c . to about 100 ° c ., preferably from about 40 ° c . to about 80 ° c ., may be employed to insure complete complex formation . generally , complete complex formation will occur within a period from a few minutes to a few hours after mixing . the complex may be recovered by precipitation using a precipitating solvent such as acetone , and further purified by crystallization or chromatography , if desired . the novel complexes of this invention can be formulated into diagnostic compositions for enteral or parenteral administration . these compositions contain an effective amount of the paramagnetic ion complex along with conventional pharmaceutical carriers and excipients appropriate for the type of administration contemplated . for example , parenteral formulations advantageously contain a sterile aqueous solution or suspension of from about 0 . 05 to 1 . 0m of a paramagnetic ion complex according to this invention . preferred parenteral formulations have a concentration of paramagnetic ion complex of 0 . 1m to 0 . 5m . such solutions also may contain pharmaceutically acceptable buffers and , optionally , electrolytes such as sodium chloride . the compositions advantageously can contain one or more physiologically acceptable , non - toxic cations in the form of a gluconate , chloride or other suitable organic or inorganic salt , including suitable soluble complexes with a chelant / ligand , to enhance safety . the chelant / ligand desirably is derived from dtpa or edta . such ligands include the ligands sell forth above used to complex the paramagnetic and or heavy metals to provide the complex formulations of this invention . advantageously , the cation - ligand complex is provided in amounts ranging from about 0 . 1 mole % to about 15 mole % of the ligand - metal complex . such physiologically acceptable , non - toxic cations include sodium ions , calcium ions , magnesium ions , copper ions , zinc ions and the like . calcium ions are preferred . a typical single dosage formulation for parenteral administration has the following composition : parenteral compositions can be injected directly or mixed with a large volume parenteral composition for systemic administration . formulations for enteral administration may vary widely , as is well - known in the art . in general , such formulations are liquids which include an effective amount of the paramagnetic ion complex in aqueous solution or suspension . such enteral compositions may optionally include buffers , surfactants , thixotropic agents , and the like . compositions for oral administration may also contain flavoring agents and other ingredients for enhancing their organoleptic qualities . the diagnostic compositions are administered in doses effective to achieve the desired enhancement of the nmr image . such doses may vary widely , depending upon the particular paramagnetic ion complex employed , the organs or tissues which are the subject of the imaging procedure , the nmr imaging equipment being used , etc . in general , parenteral dosages will range from about 0 . 01 to about 1 . 0 mmol of paramagnetic ion complex per kg of patient body weight . preferred parenteral dosages range from about 0 . 05 to about 0 . 5 mmol of paramagnetic ion complex per kg of patient body weight . enteral dosages generally range from about 0 . 5 to about 100 mmol , preferably from about 1 . 0 to about 20 mmol of paramagnetic ion complex per kg of patient body weight . the novel nmr image contrasting agents of this invention possess a unique combination of desirable features . the paramagnetic ion complexes exhibit an unexpectedly high solubility in physiological fluids , notwithstanding their substantially non - ionic character . this high solubility allows the preparation of concentrated solutions , thus minimizing the amount of fluid required to be administered . the non - ionic character of the complexes also reduces the osmolality of the diagnostic compositions , thus preventing undesired edema and other side effects . as illustrated by the data presented below , the compositions of this invention have very low toxicities , as reflected by their high ld 50 values . the low toxicity of these complexes is thought to result , in part , from the high stability constant of the complexes . the aminoalkyl moieties provide additional sites for the formation of coordination bonds with the paramagnetic metal ion , thus strengthening the coordination complex . therefore , the aminoalkyl groups not only neutralize the free carboxylic acid groups of the complexing agent , but they also participate in the formation of the complexes . the diagnostic compositions of this invention are used in the conventional manner . the compositions may be administered to a watch - blooded animal either systemically or locally to the organ or tissue to be imaged , and the animal then subjected to the nmr imaging procedure . the compositions have been found to enhance the magnetic resonance images obtained by these procedures . in addition to their utility in magnetic resonance imaging procedures , the complexing agents of this invention may also be employed for delivery of radiopharmaceuticals or heavy metals for x - ray contrast into the body . the invention is further illustrated by the following examples , which are not intended to be limiting . a dtpa morpholinoethylamide gd complex was prepared in two steps as shown below : ## str20 ## the preparation of [ n , n &# 34 ;- bis [ n - 2 (( 4 - morpholino )- ethyl - carbamoyl ] diethylenetriamine - n , n &# 39 ;, n &# 34 ;- triacetic acid specifically was carried out by the following steps : a mixture of dtpa - dianhydride ( 36 g ) and aminoethyl - morpholine ( 27 g ) in isopropanol ( 250 ml ) was stirred at ambient temperature for 16 hours . the orange solution was filtered through a fine porosity sintered glass funnel to remove undissolved impurities . the clear filtrate was poured onto ether ( 2 l ) and the mixture stirred vigorously for 1 hour . the granular precipitate was collected by filtration , washed with ether ( 3 × 1 l ), and dried . the pale tan solid thus obtained was sufficiently pure for the next step . yield 60 g ( 85 %). anal . calcd . for c 26 h 47 n 7 o 10 × o3 h 2 o : c , 50 . 13 ; h , 7 . 64 ; n , 15 . 74 . found : c , 50 . 46 ; h , 7 . 80 ; n , 15 . 69 . the preparation of [ n , n &# 34 ;- bis [ n - 2 (( 4 - morpholino ) ethyl )- carbamoylmethyl ] diethylene triamine - n , n &# 39 ;, n &# 34 ;- triaceto ]- gadolinium ( iii ) monohydrate was carried out as follows : a mixture of the ligand ( 13 . 8 g ) and gadolinium oxide ( 3 . 6 g ) in deionized water ( 70 ml ) was heated at 65 °- 70 ° c . ( water bath ) for 4 hours and stirred at ambient temperature for 16 hours . the orange solution was then filtered through a fine porosity sintered glass funnel to remove undissolved impurities . the clear filtrate was then poured onto acetone ( 2 l ) and the mixture stirred vigorously for 30 minutes . acetone was decanted off and the gummy residue was further treated with acetone ( 1 l ). the gum began to solidify and after 4 hours , the precipitate was collected by filtration , washed well with acetone ( 3 × 1 l ), dried , and recrystallized from methanol / tetrahydrofuran to afford the complex . yield , 10 g . ( 59 %). anal . calcd . for c 26 h 44 h 7 o 10 g d × 1 h 2 o : c , 39 . 54 ; h , 5 . 83 ; n , 12 . 42 ; gd , 19 . 89 . found : c , 39 . 51 ; h , 5 . 76 ; n , 12 . 47 ; gd . 19 . 79 . a stirred suspension of dtpa - dianhydride ( 7 . 0 g , 19 . 6 mmol ) in isopropanol ( 35 ml ) was treated with n , n - dimethylethylenediamine ( 3 . 8 g , 43 . 1 mmol ). the entire mixture was stirred at ambient temperature for about 18 hours . the reaction mixture was filtered to remove insoluble impurities . the clear filtrate was poured into anhydrous ether ( 2 l ) and the mixture stirred vigorously for 1 hour . the fine solid was collected by filtration , washed with ether ( 3 × 200 ml ), and dried at 0 ° c . to constant weight to yield a colorless solid , 9 . 0 g ( 82 . 0 %). anal . calcd . for c 22 h 43 n 7 o 8 . 0 . 5h 2 o ( mw 542 . 63 ); c , 48 . 71 %; h , 8 . 12 %; n , 18 . 08 %. found : c , 48 . 50 %; h , 8 . 4 %; n , 18 . 09 %. a mixture of the ligand ( 11 . 50 g , 0 , 021 mol ) and gd 2 o 3 ( 3 . 62 g , 0 . 01 mol ) in deionized water ( 50 ml was heated . after the reaction was over , the filtrate was poured into acetone ( 1 l ). the solvent was decanted off and the residue was further treated with fresh acetone ( 1 l ). the precipitate was collected by filtration and it was recrystallized from tetrahydrofuran / methanol to yield the complex as a colorless solid , 3 . 8 g ( 30 . 0 %). anal . calcd . for c 22 h 40 n 7 o 8 gd . 0 . 5h 2 o (( mw 697 . 87 ): c , 38 . 21 %; h , 5 . 79 %; n , 14 . 18 %; gd . 22 . 72 %. found : c , 38 . 54 %; h , 6 . 19 %; n , 13 . 99 %; gd , 21 . 79 %. a stirred suspension of dtpa - dianhydride ( 7 . 14 g , 0 . 02 mol ) in isopropanol ( 50 ml ) was treated with freshly distilled aminoethylthiomorpholine ( 6 . 3 g , 0 . 044 mol ). the entire mixture was stirred at ambient temperature for about 16 hours . the reaction mixture was filtered to remove insoluble impurities . the clear filtrate was taken to dryness . the gummy residue was purified by flash chromatography over reverse phase ( c - 18 ) column . this material was used as such for metal complexation . a mixture of the ligand ( 7 . 0 g , 10 . 8 mmol ) and gd 2 o 3 ( 1 . 86g , 5 . 1 mmol ) in deionized water ( 35 ml ) was heated at 67 °- 70 ° c . for 18 hours . after the reaction was over , the filtrate was poured into acetone ( 2 l ) and the mixture stirred vigorously for 30 minutes . after 1 hour , acetone was decanted off and the gummy residue was further treated with acetone ( 1 l ). the precipitate was collected , washed with acetone and recrystallized twice from acetone / water to give 4 . 5 g of colorless solid . anal . calcd . for c 26 h 44 n 7 o 8 s 2 gd × 1 . 5h 2 o : c , 37 . 54 ; h , 5 . 66 ; n , 11 . 79 ; s , 7 . 70 ; gd . 18 . 89 . found : c , 37 . 80 ; h , 5 . 51 ; n , 11 . 90 ; s , 7 . 52 ; gd , 19 . 92 the acute intravenous toxicity of the compound of example 1 was determined as follows : icr mice , at 1 to 4 per dose level , received single intravenous injections of the test substance via a lateral tail vein at the rate of approximately 1 ml / minute . the test substances were at concentrations chosen to result in dose volumes of 5 to 75 ml / kg body weight . dosing began at a volume of 10 ml / kg . dose adjustments up or down were made to closely bracket the estimated ld 50 with 4 animals per group ( 2 males and 2 females ). observations of the mice were recorded at times 0 , 0 . 5 , 1 , 2 , 4 and 24 hours and once daily thereafter for up to 7 days post injection . on the 7th day post injection , the mice were euthanized , weighed and necropsied . abnormal tissues were noted . at this time a decision was made as to whether any histopathology was to be performed and whether or not the tissues should be retained . necropsies were also performed on mice expiring after 24 hours post - injection , except for dead mice found on the weekends . the ld 50 values , along with 95 % ci were calculated using a modified behrens - reed - meunch method . the results for the complex of example 1 are reported below : ld 50 : 10 . 0 mmol / kg ( no excess ligand , 0 . 5m solution ) ld 50 : 17 . 3 mmol / 1 kg ( 5 % excess ligand as calcium salt , 0 . 5m solution ) t l or longitudinal relaxation times were measured at 90 mhz for the complex in 25 % d 2 o / 75 % h 2 o mixture at 20 mm down to 0 . 65mm . the t 1 is obtained using the spin - echo sequence on the jeol fx90q ft - nmr spectrometer . the relaxivities were determined by applying linear least - squares fit to the 1 / t 1 versus concentration data . the target correlation coefficient ( r 2 ) is about 0 . 9990 . all 13 c nmr spectra were taken on a jeol fx90qq ft - nmr spectrometer and all 1 h nmr spectra were taken on a varian gemini 300 ft - nmr spectrometer at room temperature . the ir spectrum was done on a perkin - elmer ir spectrophotometer 727 . elemental analyses were performed by galbraith laboratories of knoxville , tenn ., and atlantic microlab of norcros , ga . ph measurements were made on a corning ion analyzer 250 meter using a corning combination electrode . all spectrophotometric measurements were made on a varian cary 2215 uv / vis spectrophotometer at room temperature . all computer calculations were done on an ibm personal system 2 or an ibm - compatible pc kaypro . the relaxation rate for the complex of example 1 was 5 . 13 ± 0 . 07 mm - 1 sec - 1 at 90 mhz and 25 ° c . the correlation coefficient ( r 2 ) was 0 . 9993 . the title ligand is synthesized from dota and ch 3 och 2 ch 2 nhch 3 by following the general method reported by krejearek and tucker ( biochem . biophys . res . commun . 77 581 ( 1977 )). a mixture of the ligand from example 8 ( 10 gr . 0 . 021 mol . and gd 2 o 3 ( 3 . 6 gr , 0 . 01 mol ) in deionized water ( 50 ml ) is heated at 100 ° c . until most of the solid is dissolved . the mixture is cooled and filtered through a 0 . 2 micron filter to remove insolubles present . the filtrate is passed through an ion exchange column and the fractions containing the product are concentrated . the product may be further purified , if necessary , in accordance with conventional procedures . the procedure produces the title compound in good yield . the title ligand is synthesized from dota and 4 -( 2 - aminoethyl ) morpholine by following the method reported by krejearek and tucker ( biochem , biophys , res , commun , 77 581 ( 1977 ). the procedure of example 9 is repeated in all essential details except that the ligand used here is the mono 4 - morpholinoethylamide of dota , synthesized in example 10 , the procedure produces the title compound in good yield .
novel magnetic resonance imaging agents comprise complexes of paramagnetic ions with aminoalkylamide derivatives of diethylenetriaminepentaacetic acid or ethylenediaminetetraacetic acid or other polyaminocarboxylic or cyclic polyaminocarboxylic chelating agents , these novel imaging agents are characterized by excellent nmr image - contrasting properties and by high solubilities in physiological solutions . a novel method of performing an nmr diagnostic procedure involves administering to a warm - blooded animal an effective amount of a complex as described above and then exposing the warm - blooded animal to an nmr imaging procedure , thereby imaging at least a portion of the body of the warm - blooded animal .