deuterium ( d or 2 h ) is a stable , non - radioactive isotope of hydrogen and has an atomic weight of 2 . 0144 . hydrogen naturally occurs as a mixture of the isotopes 1 h ( hydrogen or protium ), d ( 2 h or deuterium ), and t ( 3 h or tritium ). the natural abundance of deuterium is 0 . 015 %. one of ordinary skill in the art recognizes that in all chemical compounds with a h atom , the h atom actually represents a mixture of h and d , with about 0 . 015 % being d . thus , compounds with a level of deuterium that has been enriched to be greater than its natural abundance of 0 . 015 %, should be considered unnatural and , as a result , novel over their non - enriched counterparts . all percentages given for the amount of deuterium present are mole percentages . it can be quite difficult in the laboratory to achieve 100 % deuteration at any one site of a lab scale amount of compound ( e . g ., milligram or greater ). when 100 % deuteration is recited or a deuterium atom is specifically shown in a structure , it is assumed that a small percentage of hydrogen may still be present . deuterium - enriched can be achieved by either exchanging protons with deuterium or by synthesizing the molecule with enriched starting materials . the present invention provides deuterium - enriched lenalidomide or a pharmaceutically acceptable salt thereof . there are thirteen hydrogen atoms in the lenalidomide portion of lenalidomide as show by variables r 1 - r 13 in formula i below . the hydrogens present on lenalidomide have different capacities for exchange with deuterium . hydrogen atoms r 1 - r 3 are easily exchangeable under physiological conditions and , if replaced by deuterium atoms , it is expected that they will readily exchange for protons after administration to a patient . hydrogen atoms r 9 and r 12 - r 13 may be exchanged for deuterium atoms by the action of a suitable base such as t - buok / t - buod . the remaining hydrogen atoms are not easily exchangeable for deuterium atoms . however , deuterium atoms at the remaining positions may be incorporated by the use of deuterated starting materials or intermediates during the construction of lenalidomide . the present invention is based on increasing the amount of deuterium present in lenalidomide above its natural abundance . this increasing is called enrichment or deuterium - enrichment . if not specifically noted , the percentage of enrichment refers to the percentage of deuterium present in the compound , mixture of compounds , or composition . examples of the amount of enrichment include from about 0 . 5 , 1 , 2 , 3 , 4 , 5 , 6 , 7 , 8 , 9 , 10 , 12 , 16 , 21 , 25 , 29 , 33 , 37 , 42 , 46 , 50 , 54 , 58 , 63 , 67 , 71 , 75 , 79 , 84 , 88 , 92 , 96 , to about 100 mol %. since there are 13 hydrogens in lenalidomide , replacement of a single hydrogen atom with deuterium would result in a molecule with about 8 % deuterium enrichment . in order to achieve enrichment less than about 8 %, but above the natural abundance , only partial deuteration of one site is required . thus , less than about 8 % enrichment would still refer to deuterium - enriched lenalidomide . with the natural abundance of deuterium being 0 . 015 %, one would expect that for approximately every 6 , 667 molecules of lenalidomide ( 1 / 0 . 00015 = 6 , 667 ), there is one naturally occurring molecule with one deuterium present . since lenalidomide has 13 positions , one would roughly expect that for approximately every 86 , 671 molecules of lenalidomide ( 13 × 6 , 667 ), all 13 different , naturally occurring , mono - deuterated lenalidomides would be present . this approximation is a rough estimate as it doesn &# 39 ; t take into account the different exchange rates of the hydrogen atoms on lenalidomide . for naturally occurring molecules with more than one deuterium , the numbers become vastly larger . in view of this natural abundance , the present invention , in an embodiment , relates to an amount of an deuterium enriched compound , whereby the enrichment recited will be more than naturally occurring deuterated molecules . in view of the natural abundance of deuterium - enriched lenalidomide , the present invention also relates to isolated or purified deuterium - enriched lenalidomide . the isolated or purified deuterium - enriched lenalidomide is a group of molecules whose deuterium levels are above the naturally occurring levels ( e . g ., 8 %). the isolated or purified deuterium - enriched lenalidomide can be obtained by techniques known to those of skill in the art ( e . g ., see the syntheses described below ). the present invention also relates to compositions comprising deuterium - enriched lenalidomide . the compositions require the presence of deuterium - enriched lenalidomide which is greater than its natural abundance . for example , the compositions of the present invention can comprise ( a ) a μg of a deuterium - enriched lenalidomide ; ( b ) a mg of a deuterium - enriched lenalidomide ; and , ( c ) a gram of a deuterium - enriched lenalidomide . in an embodiment , the present invention provides an amount of a novel deuterium - enriched lenalidomide . examples of amounts include , but are not limited to ( a ) at least 0 . 01 , 0 . 02 , 0 . 03 , 0 . 04 , 0 . 05 , 0 . 1 , 0 . 2 , 0 . 3 , 0 . 4 , 0 . 5 , to 1 mole , ( b ) at least 0 . 1 moles , and ( c ) at least 1 mole of the compound . the present amounts also cover lab - scale ( e . g ., gram scale ), kilo - lab scale ( e . g ., kilogram scale ), and industrial or commercial scale ( e . g ., multi - kilogram or above scale ) quantities as these will be more useful in the actual manufacture of a pharmaceutical . industrial / commercial scale refers to the amount of product that would be produced in a batch that was designed for clinical testing , formulation , sale / distribution to the public , etc . in another embodiment , the present invention provides a novel , deuterium enriched compound of formula i or a pharmaceutically acceptable salt thereof . wherein r 1 - r 13 are independently selected from h and d ; and the abundance of deuterium in r 1 - r 13 is at least 8 %. the abundance can also be ( a ) at least 15 %, ( b ) at least 23 %, ( c ) at least 31 %,( d ) at least 38 %, ( e ) at least 46 %, ( f ) at least 54 %, ( g ) at least 62 %, ( h ) at least 69 %, ( i ) at least 77 %, ( j ) at least 85 %, ( k ) at least 92 %, and ( 1 ) 100 %. in another embodiment , the present invention provides a novel , deuterium enriched compound of formula i or a pharmaceutically acceptable salt thereof , wherein the abundance of deuterium in r 1 - r 3 is at least 33 %. the abundance can also be ( a ) at least 67 %, and ( b ) 100 %. in another embodiment , the present invention provides a novel , deuterium enriched compound of formula i or a pharmaceutically acceptable salt thereof , wherein the abundance of deuterium in r 9 and r 12 - r 13 is at least 33 %. the abundance can also be ( a ) at least 67 %, and ( b ) 100 %. in another embodiment , the present invention provides a novel , deuterium enriched compound of formula i or a pharmaceutically acceptable salt thereof , wherein the abundance of deuterium in r 1 - r 3 , r 9 , and r 12 - r 13 is at least 17 %. the abundance can also be ( a ) at least 33 %, ( b ) at least 50 %, ( c ) at least 67 %, ( d ) at least 83 %, and ( e ) 100 %. in another embodiment , the present invention provides a novel , deuterium enriched compound of formula i or a pharmaceutically acceptable salt thereof , wherein the abundance of deuterium in r 4 - r 6 is at least 33 %. the abundance can also be ( a ) at least 67 %, and ( b ) 100 %. in another embodiment , the present invention provides a novel , deuterium enriched compound of formula i or a pharmaceutically acceptable salt thereof , wherein the abundance of deuterium in r 7 - r 8 is at least 50 %. the abundance can also be ( a ) 100 %. in another embodiment , the present invention provides a novel , deuterium enriched compound of formula i or a pharmaceutically acceptable salt thereof , wherein the abundance of deuterium in r 10 - r 13 is at least 25 %. the abundance can also be ( a ) at least 50 %, ( b ) at least 75 %, and ( c ) 100 %. in another embodiment , the present invention provides an isolated novel , deuterium enriched compound of formula i or a pharmaceutically acceptable salt thereof . wherein r 1 - r 13 are independently selected from h and d ; and the abundance of deuterium in r 1 - r 13 is at least 8 %. the abundance can also be ( a ) at least 15 %, ( b ) at least 23 %, ( c ) at least 31 %,( d ) at least 38 %, ( e ) at least 46 %, ( f ) at least 54 %, ( g ) at least 62 %, ( h ) at least 69 %, ( i ) at least 77 %, ( j ) at least 85 %, ( k ) at least 92 %, and ( 1 ) 100 %. in another embodiment , the present invention provides an isolated novel , deuterium enriched compound of formula i or a pharmaceutically acceptable salt thereof , wherein the abundance of deuterium in r 1 - r 3 is at least 33 %. the abundance can also be ( a ) at least 67 %, and ( b ) 100 %. in another embodiment , the present invention provides an isolated novel , deuterium enriched compound of formula i or a pharmaceutically acceptable salt thereof , wherein the abundance of deuterium in r 9 and r 12 - r 13 is at least 33 %. the abundance can also be ( a ) at least 67 %, and ( b ) 100 %. in another embodiment , the present invention provides an isolated novel , deuterium enriched compound of formula i or a pharmaceutically acceptable salt thereof , wherein the abundance of deuterium in r 1 - r 3 , r 9 , and r 12 - r 13 is at least 17 %. the abundance can also be ( a ) at least 33 %, ( b ) at least 50 %, ( c ) at least 67 %, ( d ) at least 83 %, and ( e ) 100 %. in another embodiment , the present invention provides an isolated novel , deuterium enriched compound of formula i or a pharmaceutically acceptable salt thereof , wherein the abundance of deuterium in r 4 - r 6 is at least 33 %. the abundance can also be ( a ) at least 67 %, and ( b ) 100 %. in another embodiment , the present invention provides an isolated novel , deuterium enriched compound of formula i or a pharmaceutically acceptable salt thereof , wherein the abundance of deuterium in r 7 - r 8 is at least 50 %. the abundance can also be ( a ) 100 %. in another embodiment , the present invention provides an isolated novel , deuterium enriched compound of formula i or a pharmaceutically acceptable salt thereof , wherein the abundance of deuterium in r 10 - r 13 is at least 25 %. the abundance can also be ( a ) at least 50 %, ( b ) at least 75 %, and ( c ) 100 %. in another embodiment , the present invention provides novel mixture of deuterium enriched compounds of formula i or a pharmaceutically acceptable salt thereof . wherein r 1 - r 13 are independently selected from h and d ; and the abundance of deuterium in r 1 - r 13 is at least 8 %. the abundance can also be ( a ) at least 15 %, ( b ) at least 23 %, ( c ) at least 31 %,( d ) at least 38 %, ( e ) at least 46 %, ( f ) at least 54 %, ( g ) at least 62 %, ( h ) at least 69 %, ( i ) at least 77 %, ( j ) at least 85 %, ( k ) at least 92 %, and ( 1 ) 100 %. in another embodiment , the present invention provides a novel mixture of , deuterium enriched compound of formula i or a pharmaceutically acceptable salt thereof , wherein the abundance of deuterium in r 1 - r 3 is at least 33 %. the abundance can also be ( a ) at least 67 %, and ( b ) 100 %. in another embodiment , the present invention provides a novel mixture of , deuterium enriched compound of formula i or a pharmaceutically acceptable salt thereof , wherein the abundance of deuterium in r 9 and r 12 - r 13 is at least 33 %. the abundance can also be ( a ) at least 67 %, and ( b ) 100 %. in another embodiment , the present invention provides a novel mixture of , deuterium enriched compound of formula i or a pharmaceutically acceptable salt thereof , wherein the abundance of deuterium in r 1 - r 3 , r 9 , and r 12 - r 13 is at least 17 %. the abundance can also be ( a ) at least 33 %, ( b ) at least 50 %, ( c ) at least 67 %, ( d ) at least 83 %, and ( e ) 100 %. in another embodiment , the present invention provides a novel mixture of , deuterium enriched compound of formula i or a pharmaceutically acceptable salt thereof , wherein the abundance of deuterium in r 4 - r 6 is at least 33 %. the abundance can also be ( a ) at least 67 %, and ( b ) 100 %. in another embodiment , the present invention provides a novel mixture of , deuterium enriched compound of formula i or a pharmaceutically acceptable salt thereof , wherein the abundance of deuterium in r 7 - r 8 is at least 50 %. the abundance can also be ( a ) 100 %. in another embodiment , the present invention provides a novel mixture of , deuterium enriched compound of formula i or a pharmaceutically acceptable salt thereof , wherein the abundance of deuterium in r 10 - r 13 is at least 25 %. the abundance can also be ( a ) at least 50 %, ( b ) at least 75 %, and ( c ) 100 %. in another embodiment , the present invention provides novel pharmaceutical compositions , comprising : a pharmaceutically acceptable carrier and a therapeutically effective amount of a deuterium - enriched compound of the present invention . in another embodiment , the present invention provides a novel method for treating multiple myeloma comprising : administering to a patient in need thereof a therapeutically effective amount of a deuterium - enriched compound of the present invention . in another embodiment , the present invention provides an amount of a deuterium - enriched compound of the present invention as described above for use in therapy . in another embodiment , the present invention provides the use of an amount of a deuterium - enriched compound of the present invention for the manufacture of a medicament ( e . g ., for the treatment of multiple myeloma ). the present invention may be embodied in other specific forms without departing from the spirit or essential attributes thereof . this invention encompasses all combinations of preferred aspects of the invention noted herein . it is understood that any and all embodiments of the present invention may be taken in conjunction with any other embodiment or embodiments to describe additional more preferred embodiments . it is also to be understood that each individual element of the preferred embodiments is intended to be taken individually as its own independent preferred embodiment . furthermore , any element of an embodiment is meant to be combined with any and all other elements from any embodiment to describe an additional embodiment . the examples provided in the definitions present in this application are non - inclusive unless otherwise stated . they include but are not limited to the recited examples . the compounds of the present invention may have asymmetric centers . compounds of the present invention containing an asymmetrically substituted atom may be isolated in optically active or racemic forms . it is well known in the art how to prepare optically active forms , such as by resolution of racemic forms or by synthesis from optically active starting materials . all processes used to prepare compounds of the present invention and intermediates made therein are considered to be part of the present invention . all tautomers of shown or described compounds are also considered to be part of the present invention . “ host ” preferably refers to a human . it also includes other mammals including the equine , porcine , bovine , feline , and canine families . “ treating ” or “ treatment ” covers the treatment of a disease - state in a mammal , and includes : ( a ) preventing the disease - state from occurring in a mammal , in particular , when such mammal is predisposed to the disease - state but has not yet been diagnosed as having it ; ( b ) inhibiting the disease - state , e . g ., arresting it development ; and / or ( c ) relieving the disease - state , e . g ., causing regression of the disease state until a desired endpoint is reached . treating also includes the amelioration of a symptom of a disease ( e . g ., lessen the pain or discomfort ), wherein such amelioration may or may not be directly affecting the disease ( e . g ., cause , transmission , expression , etc .). “ therapeutically effective amount ” includes an amount of a compound of the present invention that is effective when administered alone or in combination to treat the desired condition or disorder . “ therapeutically effective amount ” includes an amount of the combination of compounds claimed that is effective to treat the desired condition or disorder . the combination of compounds is preferably a synergistic combination . synergy , as described , for example , by chou and talalay , adv . enzyme regul . 1984 , 22 : 27 - 55 , occurs when the effect of the compounds when administered in combination is greater than the additive effect of the compounds when administered alone as a single agent . in general , a synergistic effect is most clearly demonstrated at sub - optimal concentrations of the compounds . synergy can be in terms of lower cytotoxicity , increased antiviral effect , or some other beneficial effect of the combination compared with the individual components . “ pharmaceutically acceptable salts ” refer to derivatives of the disclosed compounds wherein the parent compound is modified by making acid or base salts thereof . examples of pharmaceutically acceptable salts include , but are not limited to , mineral or organic acid salts of the basic residues . the pharmaceutically acceptable salts include the conventional quaternary ammonium salts of the parent compound formed , for example , from non - toxic inorganic or organic acids . for example , such conventional non - toxic salts include , but are not limited to , those derived from inorganic and organic acids selected from 1 , 2 - ethanedisulfonic , 2 - acetoxybenzoic , 2 - hydroxyethanesulfonic , acetic , ascorbic , benzenesulfonic , benzoic , bicarbonic , carbonic , citric , edetic , ethane disulfonic , ethane sulfonic , fumaric , glucoheptonic , gluconic , glutamic , glycolic , glycollyarsanilic , hexylresorcinic , hydrabamic , hydrobromic , hydrochloric , hydroiodide , hydroxymaleic , hydroxynaphthoic , isethionic , lactic , lactobionic , lauryl sulfonic , maleic , malic , mandelic , methanesulfonic , napsylic , nitric , oxalic , pamoic , pantothenic , phenylacetic , phosphoric , polygalacturonic , propionic , salicyclic , stearic , subacetic , succinic , sulfamic , sulfanilic , sulfuric , tannic , tartaric , and toluenesulfonic . table 1 provides compounds that are representative examples of the present invention . when one of r 1 - r 13 is present , it is selected from h or d . table 2 provides compounds that are representative examples of the present invention . where h is shown , it represents naturally abundant hydrogen . numerous modifications and variations of the present invention are possible in light of the above teachings . it is therefore to be understood that within the scope of the appended claims , the invention may be practiced otherwise that as specifically described herein .
the present application describes deuterium - enriched lenalidomide , pharmaceutically acceptable salt forms thereof , and methods of treating using the same .