N-TRITYL ASPARTIC ACID DERIVATIVES FOR PREPARING PHOSPHONATE NMDA ANTAGONISTS

Abstract: The present invention related to novel (R)-dimethyl N-tritylaspartate and novel (R)-alkyl N-trityl-4-oxo-5-phosphononorvalinate derivatives which are useful in the preparation of the class of beta-ketophosphonate NMDA antagonists.

Description: N-TRITYL ASPARTIC ACID DERIVATIVES FOR PREPARING PHOSPHONATE NMDA ANTAGON The present invention is related to novel (R) -dimethy 5 N-tritylaspartate and novel (R) -alkyl N-trityl-4-oxo-5- phosphononorvalinate derivatives which are useful in the preparation of a class of beta-ketophosphonate NMDA antagonists . 0 The class of beta-ketophosphonate NMDA antagonists are important in the treatment of epilepsy, nerve trauma such as that caused by stroke, cardiac arrest, hypoglycemia, an physical damage to either the brain or spinal cord, neurogenerative diseases, anxiety and for the relief of 5 pain [European Application No. 91107955.6 of Jeffrey P. Whitten entitled Heterocyclic-NMDA Antagonists, filed May 16, 1991]. This class of excitatory amino acid antagonist which act at the NMDA receptor complex can be described by formula I wherein R is hydrogen, methyl or ethyl: (R)-4-Oxo-5-phosphononorvaline derivatives of formula have been synthesized by protecting (R)-aspartic acid as the CBZ oxazolone, converting the resulting acid to an ac chloride and then coupling with a cuprate to form the bet ketophosponate. A two step deprotection yielded the desired (R)-4-oxo-5-phosphononorvaline derivative of formula I after chromatography. The novel {R)-dialkyl N-tritylaspartate and novel (R) alkyl N-trityl-4-oxo-5-phosphononorvalinate derivatives of the present invention are useful in the preparation of the class of beta-ketophosphonate NMDA antagonists. These compounds afford the (R)-4-oxo-5-phosphononorvaline derivatives of formula I with a high retention of chiralit from readily available (R)-aspartic acid. In addition, th use of the novel (R)-dialkyl N-tritylaspartate and novel (R)-alkyl N-trityl-4-oxo-5-phosphononorvalinate derivative of the present invention allows for a shorter synthesis with higher yields and avoids the use of copper. Further, the use of (R)-dimethyl N-tritylaspartate and (R)-methyl N trityl-4-oxo-5-phosphononorvalinate derivatives of the present invention provides stable crystalline materials at every step thereby avoiding the necessity of chromatography. SUMMARY OF THE INVENTION The present invention provides novel (R)-dialkyl N- tritylaspartate of formula II and novel (R)-alkyl N-trityl 4-oxo-5-phosphonovalinate derivatives of formula-III. wherein R and R' are simultaneously methyl or ethyl. The present invention further provides a method of using (R)-dialkyl N-tritylaspartate of formula II comprising the steps of (a) reacting (R)-dialkyl N- tritylaspartate of formula II with an appropriate etallo dimethyl methylphosphonate to give a (R)-alkyl N-trityl-4- oxo-5-phosphononorvalinate derivative of formula III and (b) reacting said (R)-alkyl N-trityl-4-oxo-5- phosphononorvalinate derivative of formula III with a suitable aqueous acid or trimethylsilyl iodide. It is preferred that R and R 1 are simultaneously methyl. As use herein, Ph represents an unsubstituted phenyl ring. The present invention further provides a process for preparing the (R)-4-oxo-5-phosphononorvaline derivatives o formula I comprising the steps of (a) reacting (R)-dialkyl N-tritylaspartate of formula II with an appropriate metall dimethyl methylphosphonate to give a (R)-alkyl N-trityl-4- oxo-5-phosphononorvalinate derivative of formula III and (b) reacting said (R)-alkyl N-trityl-4-oxo-5- phosphononorvalinate derivative of formula III with a suitable acid or a suitable trimethylsilyl halide. It is preferred that R and R' are simultaneously methyl. DETAILED DESCRIPTION OF THE INVENTION. The novel (R)-dialkyl N-tritylaspartate of formula II and novel (R)-alkyl N-trityl-4-oxo-5-phosphononorvalinate derivatives of formula III can be prepared by utilizing procedures and techniques well known and appreciated by on of ordinary skill in the art. A general synthetic procedure for preparing these compounds is set forth in Scheme A. Scheme A (1) (2) ) Scheme A provides a synthetic procedure for preparing (R)-dialkyl N-tritylaspartate of formula II and novel (R)- alkyl N-trityl-4-oxo-5-phosphononorvalinate derivatives of formula III. In step a, (R)-aspartic acid (1) is esterified to give (R)-dialkγlaspartate (2) by techniques and procedures well known and appreciated by one of ordinary skill in the art. For example, (R)-aspartic acid (1) is converted to (R)- dialkylaspartate (2) by adding a suitable activating agent such as thionyl chloride, to a suspension of the (R)- aspartic acid (1) in a suitable alcohol such as methanol o ethanol. The reactants are typically stirred together for a period of time ranging from 10 hours to 3 days and at a temperature range of from 0°C to room temperature. The resulting (R)-dialkylaspartate (2) is recovered from the reaction zone by evaporation of the solvent. In step b, (R)-dialkylaspartate hydrochloride (2) is converted to the (R)-dialkyl N-tritylaspartate of formula II by treating (R)-dialkylaspartate hydrochloride (2) with triphenylmethyl chloride and a suitable base, such as triethylamine. The reactants are typically contacted in a suitable organic solvent such as acetonitrile. The reactants are typically stirred together at room temperature for a period of time ranging from 2-24 hours. The resulting (R)-dialkyl N-tritylaspartate of formula II is recovered from the reaction zone by extractive methods as is known in the art. In step c, the (R)-dialkyl N-tritylaspartate of formula II is converted to the (R)-alkyl N-trityl-4-oxo-5- phosphononorvalinate derivatives of formula III by treating the (R)-dialkyl N-tritylaspartate of formula II with a suitable metallo methyl dimethylphosphonate of structure (3). Suitable metallo compounds of structure (3) include lithium methyl dimethylphosphonate, potassium methyl dimethylphosphonate, sodium methyl dimethylphosphonate, magnesium methyl dimethylphosphonate and the like. The reactants are typically contacted in a suitable anhydrous organic solvent such as tetrahydrofuran. The reactants ar typically stirred together for a period of time ranging from 15 minutes to 5 hours and at a temperature range of from -78 β C to -40°C. The (R)-alkyl N-trityl-4-oxo-5- phosphononorvalinate derivatives of formula III is recovered from the reaction zone by acid neutralization followed by extractive methods as is known in the art. It may be purified by recrystallization. Starting materials for use in Scheme A are readily available to one of ordinary skill in the art. The following examples present typical syntheses as described in Scheme A. These examples are understood to b illustrative only and are not intended to limit the scope of the present invention in any way. As used herein, the following terms have the indicated meanings: "g" refers t grams; "mmol" refers to millimoles; "mL" refers to milliliters; "bp" refers to boiling point; " p" refers to melting point; "°C" refers to degrees Celsius; "mm Hg" refers to millimeters of mercury; "μL" refers to microliters; "μg" refers to micrograms; and "μM" refers to micromolar. Example 1 (R)-Dimethyl N-tritylaspartate Step a: (R)-Dimethylaspartate hydrochloride Suspend (R)-aspartic acid (39.9g, 0.30mol) in methanol (250m ), cool to 0°C and place under a nitrogen atmosphere Add, by dropwise addition over 0.5 hours, thionyl chloride (50.lg, 0.42mol). Allow to warm to room temperature and stir for 48 hours. Evaporate the solvent, triturate the residue with ether and collect by filtration to give the title compound as a white solid (60.lg, 100%). 1H NMR (DMSO-d 6 ) δ 4.3 (t, IH) , 3.75 (s, 3H), 3.67 (m, 2H) Step b; (R)-Dimethyl N-tritylaspartate Mix (R)-dimethyl aspartate hydrochloride (57g, 0.288mol), triphenylmethylchloride (75.Og, 0.27mol) and acetonitrile. Stir well and add, by dropwise addition over 2 hours, triethylamine (85mL, 0.27mol). Stir the resulting mixture for a further 4 hours then add ethyl acetate (500mL). Was with saturated sodium chloride (500mL) and add chloroform (lOOm ). Separate the organic phase, dry (Na2S04) and evaporate to a residue. Add methanol (250mL) and stir to effect crystallization. Filter to give the title compound as a white solid (83g f 74%). IH NMR (CDC1 3 ) 6 7.5-7.25 (m, 15H) , 4.78 (m, IH) , 4.72 (s, 3H), 3.3 (s, 3H), 2.95 (bs, IH), 2.62 (m, 2H) . Example 2 (R)-Methyl N-trityl-4-oxo-5-(dimethylphosphono)norvalinate Dissolve dimethyl methylphosphonate (83mL, 0.766mol) in anhydrous tetrahydrofuran (800mL), cool to -78°C and place under an inert atmosphere. Add, by dropwise addition over 15 minutes, n-butyllithium (306m of a 2.5M solution, 0.766mol). Stir the resulting clear solution for a further 0.5 hour. While maintaining the solution at -78°-C, add by dropwise addition over 15 minutes, to another solution of (R)-dimethyl N-tritylaspartate (71g r 0.182mol) in anhydrous tetrahydrofuran (200mL) also at -78°C. Stir for a further 0.5 hours, quench with acetic acid (45mL) and warm to room temperature. Add ethyl acetate (500mL) and saturated sodiu bicarbonate (250mL). Separate the organic phase, filter through silica gel and evaporate the solvent to gi a solid residue. Crystallize (t-butylmethyl ether/hexane) to give the title compound as a white solid (61.Og, 69%). IH NMR (CDC1 3 ) δ 7.5-7.25 (m, 15H) , 3.82 (s, 3H) , 3.79 (s, 3H), 3.75 (t, 3H), 3.08 (d, 2H) , 2.88 (m, 2H) , 1.65 (bs, IH). The (R)-4-oxo-5-phosphononorvaline derivatives of formula I can be prepared from the (R)-alkyl N-trityl-4- oxo-5-phosphononorvalinate derivative of formula III as se forth in Scheme B. Scheme B la lb Scheme B provides a general method for using the (R)- alkyl N-trityl-4-oxo-5-phosphononorvalinate derivatives of formula III in order to form the (R)-4-oxo-5- phosphononorvaline derivatives of formula I. In step ai, the phosphoπate methyl ester functionalities of the appropriate (R)-alkyl N-trityl-4- oxo-5-phosphononorvalinate derivatives of formula III are cleaved to give the corresponding (R)-4-oxo-5- phosphononorvaline derivative of formula la. For example, the appropriate (R)-alkyl N-trityl-4-ox 5-phosphononorvalinate derivative of formula III is trea with two molar equivalents of a suitable trimethylsilyl halide such as trimethylsilyl iodide or trimethylsilyl bromide. The reactants are typically contacted in a suitable organic solvent such as acetonitrile or methyle chloride. The reactants are typically stirred together room temperature for a period of time ranging from 2-10 hours. The resulting (R)-4-oxo-5-phosphononorvaline derivative of formula la is recovered from the reaction zone by extractive methods as is known in the art. It m be purified by chromatography. In step a 2/ the phosphonate methyl ester and carboxylate functionalities of the appropriate (R)-alkyl trityl-4-oxo-5-phosphononorvalinate derivatives of formul III are cleaved to give the corresponding (R)-4-oxo-5- phosphononorvaline derivative of formula lb. For example, the appropriate (R)-alkyl N-trityl-4-ox 5-phosphononorvalinate derivative of formula III is treat with a suitable strong aqueous mineral acid, such as hydrochloric acid, hydrobromic acid, sulfuric acid and th like. The reactants are typically stirred together for a period of time ranging from 5 minutes to 2 hours and at a temperature range of from room temperature to reflux. Th resulting (R)-4-oxo-5-phosphononorvaline derivative of formula lb is recovered from the reaction zone as its hydrochloride salt by evaporation of the solvent. It may be converted to its free base by treatment with propylene oxide as is known in the art. In optional step b, the carboxylate functionality of the appropriate (R)-4-oxo-5-phosphononorvaline derivative of formula la is cleaved to give the (R)-4-oxo-5- phosphononorvaline derivative of formula lb as described previously in step ≥ 2 - The following example presents a typical method of using the (R)-alkyl N-trityl-4-oxo-5-phosphononorvalinate derivatives of formula III in order to form the (R)-4-oxo- 5-phosphononorvaline derivatives of formula I. This example is understood to be illustrative only and is not intended to limit the scope of the present invention in any way. Example 3 (R)-4-0xo-5-phosphononorvaline Add (R)-methyl N-trityl-4-oxo-5(dimethyIphophono)- norvalinate (l.Og, 2.02mmol) to aqueous 5M hydrochloric acid (lOmL) and reflux for 15 hours. Evaporate the resulting solution to give a residue and take the residue up in methanol (8ml.). Add propylene oxide (0.5mL) and stir for 0.5 hours. Filter the resulting solid and wash with methanol (5mL). Take the resulting solid up in water (30mL) and freeze dry to give the title compound as a white solid. IH NMR (D 2 0, 300MHz) 4.3 (m, IH) , 3.48 (m, 2H) , 3.12 (m, 2H); "C NMR (D 2 0, 300MGZ) 208.283, 175,121, 52.161, 52.110, 46,106? 31P NMR (D 2 0, 121MHz) 12.4; S (FAB) m/e 212 (M+H+) , 167 (M+H+ -HC0 2 H) , 139 (-i-H 3 P0 3 CH 2 COCH 3 ), 132 (+CH 3 COCH 2 CH(NH 3 +)C0 2 H) . Anal. Calcd for C 5 Hι 0 NO 6 • 0.5H 2 O: C, 27.28; H, 5.04; N, 6.45; Found: C, 27.38; H, 4.77; N, 6.45 (Tg% loss = 4.4).

Claims: WΞAT IS CLAIMED IS: 1. A compound of the formula wherein R and R 1 are simultaneously methyl or ethy 2. A compound of the formula wherein R is methyl or ethyl. 3. A process for preparing (R)-4-oxo-5- phosphononorvaline derivatives comprising the steps oft (a) reacting a compound of the Claim 1 with an appropriate metallo dimethyl methylphosphonate t give a compound of Claim 2; (b) reacting said compound of Claim 2 with a suitable acid. 4. A process for preparing (R)-4-oxo-5- phosphononorvaline ester derivatives comprising reacting compound of Claim 2 with a suitable trimethylsilyl halide. 5. A process for preparing (R)-4-oxo-5- phosphononorvaline derivatives comprising the step of: a) reacting a compound of Claim 2 with a suitable trimethylsilyl halide to give a (R)-4-oxo-5- phosphononorvaline ester derivatives; b) reacting said (R)-4-oxo-5-phosphononorvaline ester derivatives with a suitable acid. 6. A method of using a compound of Claim 1 in order to form a compound of Claim 2 comprising reacting a compound of the Claim 1 with an appropriate metallo dimethyl methylphosphonate. 7. A method of using a compound of Claim 2 in order to form (R)-4-oxo-5-phosphononorvaline derivatives comprising reacting said compound of Claim 2 with a suitable acid. " 8. A method of using a compound of Claim 2 in order to form (R)-4-oxo-5-phosphononorvaline ester derivatives comprising reacting compound of Claim 2 with a suitable trimethylsilyl halide. 9. A method of using a compound of Claim 2 in order to form a (R)-4-oxo-5-phosphononorvaline derivatives comprising the steps of: a) reacting a compound of Claim 2 with a suitable trimethylsilyl halide to give a (R)-4-oxo-5- phosphononorvaline ester derivatives; b) reacting said (R)-4-oxo-5-phosphononorvaline ester derivatives with a suitable acid. 10 15 20 25 30 35

Inventors: RUDISILL DUANE E, WHITTEN JEFFREY P, RUDISILL, DUANE, E., WHITTEN, JEFFREY, P.
Applicants: MERRELL DOW PHARMA, MERRELL DOW PHARMACEUTICALS INC.
Application year: 1992
Main classification: C07F9
IPC codes: A61K31, A61P25, C07C229, C07F9