Indian Journal of Chemistry Vol. 39B, January 2000, pp. 10 - 1 5

Synthetic and biotransformation studies on prochiral non-proteinogenic amino

acids: Diethyl a-acetamido, a-alkylmalonates

Amarjit Singh, Ashok K Prasad, William Errington), Yuri N Belokon2, Konstantine A Kochetko�, Rajendra K Saxena3, Subhash C Jain & Virinder S Pannar*

Department of Chemistry, University of Delhi, Delhi 1 10 007, India 'Department of Chemistry, University of Warwick, Coventry CV4 7AL, UK

2A.N. Nesmeyanov Institute of Organoelement Compounds, Russian Academy of Sciences, Vavilov 28, 1 1 781 3 Moscow, Russia

3Department of Microbiology, University of Delhi,South Campus. Benito Juarez Marg, New Delhi 1 10 02 1 , India

Received 24 June 1999; accepted 27 September 1999

Nine diethyl a-acetamido, a-alkylmalonates 3-1 1 (alkyl=methyl, benzyl, 3-fluorobenzyl, 4-fluorobenzyl, 2,6-difluorobenzyl, 3-trifluoromethylbenzyl, 4-trifluoromethylbenzyl, 2-chlorobenzyl and 3-chlorobenzyl) have been synthesised in three steps starting with diethyl malonate in overall yields of 49-90%. The structures of C-alkylated acetamidomalonates have been established on the basis of their spectral data, the structures of two compounds 9 and 1 1 are also confirmed on the basis of their X-ray crystallographic studies. Further, the X-ray crystal structure of the chiral monoethyl ester of a-acetamidomalonic acid 1 has been studied. None of our C-alkylated acetamidomalonate has been found to be a substrate for lipase-catalysed enantiodifferentiating deesterification! hydrolysis of the symmetric diester groups.

Amino acids are well-known for their wide natural occurrence and are one of the five major classes of natural products '-3 . Among them, dicarboxylic amino acids have, recently drawn the attention because of their specific function in biological systems. For example, glutamic acid is known to mediate synaptic excitation, and therefore is involved in the nerve signal transmission in mammalian central nervous system by binding to excitatory amino acid receptors which play a vital role in a number of physiological processes related to memory and learning4-6 and the neuroendocrine regulation of several hormonal systems,,8. Again, peptide derivatives of aminomalonic acid, first representative of the homologous a-amino dicarbo?,-ylic acid series have been found to play an important role as enzyme inhibitors, e.g. of renin9,10 and HIV - 1 proteasel l .

Aminomalonic acid has a prochiral centre and all its diesters having two different alkyl moieties should be chiral. Obviously, the chiral moiety of the aminomalonic acid derivatives might become an important stereocontrolling element, if this chiral residue is incorporated in the peptide chain. Recently, we have investigated the enzymatic hydrolysis of diethyl acetamidomalonate and have demonstrated,

for the first time, that the reaction catalysed by a­chymotrypsin In phosphate buffer at room temperature proceeds enantioselectively with the formation of dextrorotatory monoester'2. This is the first report on the preparation of the chiral monoethyl ester of a-acetamidomalonic acid 1, its X-ray crystal structure is shown in Figure 1 . However, the chiral monoester formed unde-rgoes -in situ · racemisation which is attributed to the presence of highly acidic hydrogen atom at the a-carbon. This observation

Figure l-X-ray crystal structure of mono ethyl ester of a­acetamidomalonic acid 1

SINGH et al. : STUDIES ON PROCHlRAL NON-PROTEINOGENIC AMINO ACIDS

o I I o H C-OR

o

O H 1 1 1 C -� II I / CH,-C -N-C-H \

C-�

I I

CH:tCN, K�Ol alkyl halide, reflux

II I 2/ 3 CH3-C-N-C-CHr-R \

C-OCiis II . o

1. R - H

2. R - �5

o

2' 4. R =-Q'"

8' 5. R = 3-FoCeH4 6. R = 4-F-C6H4 . 7. R = 2, 6-FrCeH3 8. R = 3-CFMH4 8. R = 4-CFMH4 10. R = 2-CI-CeH4 11 . R = 3-CI-CeH4

Scheme I

prompted us to- synthesise a-alkylated diethyl acetamidomalonates with an aim to prepare optically . . pure derivatives of a-amino dicarboxylic acids.

Nine diethyl a-acetamido a-alkylated malonates 3-11 were . synthesised in three steps starting with the isonitros,?ylation of diethyl acetamidomalonate, reduction , followed by in situ N-acetylation of the resulted isonitrosomalonate to diethyl a-acetamido­malonate 2, followed by its alkylation with appropriate alkyl halide (Scheme I). All alkylated acetamidomalonates 3-11 are new compounds and have been identified on the basis of their ElMS, ClMS, IH NMR, 13C NMR, IR and UV spectral data.

Earlier we have suc�essfully used lipases to carry out regio-, chemo- and enantioselective reactions on different classes of compounds with a view to synthesising bioactive molecules or their precursors in optically pure/enriched forms3,13-11. In the present investigation, we have screened a-chymotrypsin, porcine pancreatic lipase, Candida rugosa lipase and Aspergillus carneus lipase in phosphate buffer or in organic solvents at room temperature or at 45-50 °C for enantiodifferentiating deestePfication of diethyl a­acetamido a-alkylmalonates 3-11 with an aim to prepare enantiomerically pure ·half esters. Even after prolonged reaction time, hydrolysisldeesterification of diethyl malonates 3-1 1 was not observed with any of the enzymes under study. Further work to desymmetrise these prochiral diesters is in progress.

X-ray crystallography The X-ray crystal structure of the chiral monoethyl

ester of a-acetamidomalonic acid 1 is shown in Figure 1 . Further, structures determined on the basis of spectral analysis of the two compounds, i.e. diethyl a-acetamido, a-( 4-trifluoromethylbenzyl)malonate 9

and diethyl a-acetamido, a-(3-chlorobenzyl)malonate 1 1 were confirmed by X-ray crystallography. Schematic representation of the molecular structures of compounds 9 and 1 1 are shown in Figure 2 and Figure 3, respectively.

Fez

-enS) b Figure 2--X-ray crystal structure of diethyl a-acetamido, a-(4-

trifluoromethylbenzyl)malonate 9

12 INDIAN J CHEM, SEC B, JANUARY 2000

Figure 3--X-ray crystal structure of diethyl a-acetomido, a-(3- ; chlorobenzyl)malonate 11

Experimental Section General - Melting points were determined either

on a Mettler FP62 melting point apparatus ' or in a , sulphuric acid bath and are uncorrected. EI mass ' spectra were recorded on a Varian Mat 3 1 1 A mass spectrometer at 70 eV. The IH and BC NMR spectra were recorded in CDCh, either at 300 or 250 MHz and at 75 or 62.9 MHz on a Gemini 300 or a Bruker ' I AC-250 spectrometer, respectively using TMS as an ; internal standard. Coupling conStants (J) are in Hz. IR .

(KBr) and UV (MeOH) were recorded on a Shimadzu model 435 and a Beckman DU-2 spectrophotometer, ; respectively. Analytical TLCs were performed on ' precoated E Merck silica gel 60 F2s4 aluminium . plates. a-Chymotrypsin from bovine pancreas, lyophilized powder, was obtained from Fluka ' (Switzerland) and used as such. Porcine pancreatic lipase (Type II) and Candida rugosa l ipase (Type i VII) were purchased from Sigma Chemical Co. I (USA) and used after keeping in vacuo over P20S for I 25 hr. Amino P lipase was obtained from Amano ' (Japan). Aspergillus cameus lipase was isolated from Aspergillus came us (a new lipase producer) and used : as lyophilised powderl6. .

Preparation of diethyl acetamidomalonate 2. The title comraound 2 was synthesised by literature procedure 8 by the reaction of diethyl malonate with sodium nitrite and acetic acid followed by reduction i and in situ N-acetylation of the resulting diethyl isonitrosomalonate, 2 was obtained as a white , crystalline solid in 87% yield, mp 96-97 °c (lit. 18 mp :

95-97°C); CIMS mlz (% reI. int.): 2 1 8([M+l tXI00), 1 76(6), 145(5), 1 19(3), 102(20), 58(5) and. 44(4); 1H NMR (250 MHz, CDC h) : 0 I .3O(t, J = 7. 1 Hz, 6H, 2 x CH2CH3), 2.08(s, 3H, CH3CO), 4.25(m, 4H" 2 x OCH2), 5 . 1 8(d, .J = 7. 1 Hz, IH, C-2H) and 6.81(brd, J = 7 . 1 Hz, IH, NH); \3e NMR (62.5 MHz, CDC h) : 0 1 3 .77(2 x CH2CH3), 22.44(CH3CO); 56.26(C-2), 62.32(2 x OCH2), and 1 66.32 and, 169.75(3 x CO); IR: 3300, 3 100, 3050, 1 770, 1 745, 1 645, 1 550, 1450, 1380, p40, 1270, 1 160, 10 10, 920, 860 and 710 cm-I; UV: 204 nm.

General p�ocedure for the preparation of diethyl a-acetamido, a-alkylmalonates 3-1 1. A mixture 'of ! diethyl acetamidomalonate (2, 10 mmoles), alkyl I halid� (methyl iodide, benzyl bromide, 3-fluorobenzyl , bromide, 4-fluorobenzyl bromide, 2,6-difluorobenzyl bromide, 3-trifluoromethylbenzyl bromide 4-. ' ' trlfluoromethylbenzyl bromide, 2-chlorobenzyl bromide or 3-chlorobenzyl bromide; 1 5 mmoles) and

, ignited potassium carbonate (40 mmoles) in dry acetonitrile (30 mL) was refluxed for 1 5-20 hr. Potassium carbonate was filtered off, solvent removed under reduced pressurp. and the crude product was ' purified by crystalh�ation · to afford the title compounds 3-1 1 in 55-99% yields.

Diethyl a-acetamido, a-methylmalonate 3. Crystallised from petrol-ethyl acetate mixture as light yellow needles (2. 1 2 g) in 92% yield, mp 93-94 °c . (Found: C, 52. 1 0; H, 7.40; N, 6.00. Calc. for

. CIOH17NOs: C, 5 1 .90; H, 7.36; N, 6.06 %); ElMS mJz (% reI. int.): 23 1�) (1), 1 86(5), 1 59(5), 158(61), 1 17(6), 1 1 6(100), 88( 1 5), 43(1 8) and 42(30); IH NMR (300 MHz) : 0 1 .25(t, J = 7. 1 Hz, 6H, 2 x CH2CHj), 1 .75(s, 3H, C-3H), 2.00(s, 3H, CH3CO), 4.24(m, 4H, 2 x.OCH2) and 6.90(brs, I H, NH);\3C NMR (75.0 MHz) : 013 .86(2 x CH2 CH3), 20.89(C-3), ; 22.95(CH3CO), 62.44(2 x OCH2), 62.92(C-2) and ' 1 68.8 1 and 168.97(3 x CO); IR: 3300, 3 1 00, 3050, ; 1 770, 1 745, 1 645, 1 550, 1450, 1380, 1340, 1300, 1 270, 1220, 1 160, 10 10, 920, 860 and 7 10 cm-I; UV:

· 204 nm.

Diethyl a-acetamido, a-benzylmalonate 4. Crystallised from petrol-ethyl acetate mixture as colourless needles (3.00 g) in 98% yield, mp 1 02 °C; ElMS mlz (% reI. int.): 307(M) ( 1 0), 262(7), 248(71), 234( 1 8), 203(1 7), 192(77), 1 74(94), 1 58(60), 1 1 8(62), 91( 100), 65(14) and 43(93); CIMS mlz l(%

. �

. SINGH et al. : STUDIES ON PROCHIRAL NON-PROTEINOGENIC AMINO ACIDS . 13

",

. rel. int.): 308([M+l]l ( 100), 262(1 2), 192(7), 146(3) . and 9 1(7); IH NMR (250 MHz) : B L29(t, J = 7 . 1 Hz, 6H, 2 x CH2CHJ), 2.01(s, 3H, CH3CO), 3 .64(s, 2H, C- ' 3H), 4.26 and 4.30(2q, 2H each, J = 7.0 and 7. 1 Hz, 4H, 2 x OCH2), 6.54(s, I H, NH), and 7.0 1 and 7.25(2m, 5H, CJ!s); I3C NMR (62.5 MHz): B 1 3.90(2 x CH2 CH3 ), 22.90(CH3 CO), 37.72(C-3), 62.50(2 x OCH2), 67.13(C-2), 127.08, .128.20, 129.77 and 135 . 19(aromatic carbons), and 1 67.41 and 168.93(3 x CO); IR: 3400, 3"000, 1 75{), 1640, 1 5 1 5, 1450, 1370, 1280, 1 180, 1 080, 1 040, 10 10, 860 and 740 cm-\ UV: 2 1 6, 257 and 263 om.

Diethyl a-aeetamido, a-(3-fluorobeozyl)malonate

5. Crystallised from petrol-chlorofonn mixture as a colourJess solid (2.76 g) in 85% yield, mp 1 1 1 °C; ElMS mlz (% ret. int.): 325�) (7), 280(4), 266(30), 252(14), 2 1 0(55), 1 74(55), 1 55(42), 1 36(34), 109(57), 83(1 8) and 43( 100); CIMS mlz (% reI. int.): 326([M+l t) ( 100), 280(9), 27 1(24), 210( 1 2), 1 74(9), 109(10), 83(5), 60(4) and 43(4); IH NMR (250 MHz): B 1 .29(t, J = 7. 1 Hz, 6H, 2 x CH2CH3), 2.03(s, 3H, CH3CO), 3 .65(s, 2H, C-3H), 4.27 and 4.30(2q, 2H each, J = 7.0 Hz and 7. 1 Hz, 4H, 2 x OCH2), 6.57(s, IH, NH), 6.75(m, 2H; C-2'H and C-4'H), 6.95(m, IH, C-6'H) and 7.25(m, IH, C-5'Ii); J3C NMR (62.5 MHz) : B 1 3 .95(2 x CH2CH3), 22.97(CH3CO), 37.48(C-3), 62.73(2 x OCH2), 67.02(C-2), 1 1 3 .94, 1 14.28, 1 16.55, 1 16.89(C-2' and C-4'), 125 .50 and 1 25.55(C-6'), 129.63 and 129.76(C-5'), 137.71 and 137.83(C-l '), 160.63 and 164.55(C-3'), and 167.28 and 169. 1 1(3 x CO); IR: 3250, 3000, 1 750, 1 640, 1 5 1 5, 1490, 1440, 1370, 1270, 1 1 80, 1080, 1 040, 1 0 1 0, 950, 850, 780 and 690 em-I ; UV: 212, 262 and 268 nm.

Diethyl a-aeetamido, a-( 4-fluorobenzyl)malonate

6. Crystallised from petrol-chloroform mixture as a colourless solid (3 .2 1 g) in 99% yield, mp 143°C; ElMS mlz (% reI. int.): 325(M+) (4), 280(5), 266(44), 210(37), 193(13), 1 74(52), 147(21), 136(30), 120(1 5), 109(91), 83(1 0) and 43( I QO); CIMS mlz (% reI. int.): 326([M+ 1 t) ( 100), 280(25), 2 10(7), 109(7) and 44(1); IH NMR (250 MHz) : B 1 .28(t, J= 7 . 1 Hz, 6H, 2 x CH2CH3), 2.02(s, 3H, CH3CO), 3 .62(s, 2H, C-3H), 4.24 and 4.30(2q, 2H each, J = 7.0 and 7.1 Hz, 4H, 2 x OCH2), 6.56(s, I H, NH) and 6.96(m, 4H, aromatic protons); J3C NMR (62.5 MHz) : B 1 3 .90 ' (2 x CH2CH3), 22.88(CH3CO), 36.S9(C-3), 62.59 (2 x OCH2), 67.09(C-2), 1 I4.93 and 1 1 5 .28(C-3' and

, C-S'), 1 30.88, 1 30.94, 13 1 . 1 7 and 1 3 1 .29(C�2', C-6' : and C-l '), 1 60.06 �d 163 .96(C-4') and 167.32 and . 1 69.02(3 x CO); IR: 3280, 3000, 1750, 1640, 1 5 10, 1440. 1 3 70, 1280, 1 180, 1090, 1040, 1010, 950, 840, 800 and 750 em-I ; UV: 210, 264 and 270 om.

Diethyl a-acetamido, a-(2,6-difluorobeozyl)­

malonate 7. Crystallised from petrol-chloroform mixture as a yellow coloured solid (2.70 g) in 79% yield, mp 1 0 1 °C; ElMS mlz (% reI. int.): 343�) (8), 284( 1 1), 270(16), 228(7 1), 2 10( 14), 1 74( 100), 1 54(22), 127(37), 1 09( 1 6) and 43(98); CIMS mlz (% reI . int.): 344([M+lr) ( 100), 298(1 0), 228(1 5),

. 1 74( 12) and 43(2); IH NMR (250 MHz) : B 1 .29(t, J= 7. 1 Hz, 6H, 2 x CH2CH3), 1 .97(s, 3H, CH3CO), 3 .74(s, 2H, C-3H), 4.26(m, 4H, OCH2), 6.5 1(s, IH, NH), 6.84(m, 2H, C-3'H and C-5'H) and 7.2 1(m, IH, C-4'H); \3C NMR (62.5 MHz) : B 13 .66(2 x CH2CH3), 22.50(CH3CO), · 26.08(C-3), 62.5 1 (2 x OCH2), 65.3 1 (C-2), 1 10.69, 1 10.75, 1 1 0.89, 1 1 1 .03, 1 1 1 . 1 5 and 1 1 1 . 1 7(C-l ', C-3' and C-5'), 128.89, 129.05 and 129.22(C-4'), 1 59 .94, 1 60.07, 1 64.02 and 165.00(C-2' and C-6'), and 167.4 1 and 1 68.99(3 x CO); IR: 3400, 3050, 1 740, 1685, 1630, 1 600, 1 5 10, 1480, 1370, 1330, 1300, 1280, 1 2 10, 1 090, 1 050 and 980 em-I; UV: 213, 258 and 261 nm.

Diethyl a-acetamido, a-(3-trifluoromethylbeozyl)­

malonate 8. Crystallised from petrol-ethyl acetate mixture as colourless needles (2.85 g) in 76% yield, mp 1 32°C; ElMS mlz (% reI. int.): 375(Ml (6), 3 16(23), 302(1 5), 27 1(8), 260(82), 226(1 8), 198(7), 1 86(40), 1 74(1 00), 1 59(61), 1 1 8(6), 1 09(9) and 56(5); CIMS mlz (% reI. int.): 376([M+l t) ( 100), 3 16(14), 260(22), 1 74( 19) and 102(2); IH NMR (250 MHz).:·�1 1 .30(t, J = 7 .1 Hz, 6H, 2 x CH2CH3), 2.03(s, 3H, CH3CO), 3 .72(s, 2H, C-3H), 4.24(q, J = 7 . 1 Hz, 4H, 2 x OCH2), 6.55(s, I H, NH), 7.20(d, J = 7.6 Hz, IH, C-4'H), 7.27(brs, IH, C-2'JI), 7.38(m, I H, C-5'H) and 7.50(d, J= 7.6 Hz, I H, C-6'H); \3C NMR (62.5 MHz) : 8 13 .90(2 x CH2CH3), 22.83(CH3CO), 37.45(C-3), 62.80(2 x OCH2), 67.04(C-2), 123.96, 124.02, 126.58, 126.64, 128.72, 133 . 1 8 and 136.33(aromatic carbons and CF3), and 167. 16 and 169.22(3 x CO); IR: 3300, 3050, 1 755, 1650, 1 520, 1460, 1380, 1 3'50, 1 3 10, 1280, 1 190, 1 1 70, 1 1 50, 1 1 10, 1-070, 1050, 10 10, 950, 9 1 0 and 850 em-I; UV: 214, 263 and 270 nm.

Diethyl a-acetamido, a-( 4-trifluoromethylbeozyl)­

malonate 9. Crystallised from petrol-chloroform

14 INDIAN J CHEM, SEC B, JANUARY 2000

mixture as light yellow plates (3 .22 g) in 86% yield. mp 132-33°C; ElMS rnIz (% reI. int.): 375�) (20), 330( 13), 3 1 6(60), 302(37), 271 (22), 260(1 00), 243(4), 226(39), 198( 14), 1 86(59), 1 74(94), 1 59(7 1 ) and 1 09( 10); CIMS rnIz (% reI. int.): 376([M+l t) ( 100), 330( 12), 260( 1 1), 1 74(7) and 60( 1); IH NMR (250 MHz) : 0 1 .29(t, J = 7. 1 Hz, 6H, 2 x CH2CH3), 2.03(s, 3H, CH3CO), 3 .72(s, 2H, C-3H), 4.26(m, 4H, 2 x OCH2), 6.54(s, I H, NH), 7. l 2(d, J = 8.0 Hz, 2H, C-2'H and C-6'H) and 7.5 1 (d, J = 8.0 Hz, 2H, C-3'H and C-5'H); I 3C NMR (62.5 MHz) 0 1 3 .96(2 x CH2CH3), 22.97(CH3CO), 37.55(C-3), 62.82(2 x OCH2), 66.98(C-2), 125. 1 1 , 125 . 1 7, 125 .23, 125.28, 1 30. 1 7 and 1 39.50(aromatic carbons and CF3), and 1 67.23 and 1 69.2 1(3 x CO); IR: 3220, 3050, 1 755, 1650, 1 520, 1450, 1430, 1370, 1 340, 1 300, 1280, 1200, 1 1 50, 1 1 1 0, 1 060, 1040, 10 10, 950 and 860 cm'l; UV: 2 1 9, 258 and 263 nm.

Diethyl a-acetamido, a-(2-chlorobenzyl)malonate 10. Crystallised from petrol-chloroform mixture as a colourless solid ( 1 .87 g) in 55% yield, mp 84°C; ElMS rnIz (% reI. int.): 343([M+2t) (2), 34 1 (M+) (4), 306(1 5), 268( 1 1 ), 247(58), 226(47), 1 74(97), 1 52(25), 125(48), 89( 12) and 43( 100); CIMS rnIz (% reI . int.): 342([M+l t) ( 100), 296(8), 27 1 ( 12), 247( 1 8), 226( 10), 1 74( 1 2) and 1 25(5); IH NMR (250 MHz) : 0 1 .28(1, J = 7 . 1 Hz, 6H, 2 x CH2CH3), 2.03(s, 3H, CH3CO), 3.82(s, 2H, C-3H), 4.26(m, 4H; 2 x OCH2), 6.52(s, I H, NH), 7. 1 0(m, I H, C-5'H), 7.20(m, 2H, C-4'H and C-6'H) and 7.35(m, I H, C-3'H) ; I3C NMR (62.5 MHz) : 0 1 3 .80(2 x CH2CH3), 22.9 1(CH3CO), 35 .0 1 (C-3), 62.56(2 x OCH2), 66. 1 5(C-2), 126.45, 128.56, 129.64, 1 32. 1 9, 133 .25 and 1 34.90(aromatic carbons), and 1 67.53 and 169 . 1 5(3 x CO); lR: 3240, 3000, 1 750, 1640, 1 5 1 5, 1480, 1440, 1370, 1280, 1 190, 10 10, 950 and 850 cm'l ; UV: 2 14, 267 and 274 Dm.

Diethyl a-acetamido, a-(3-chlorobenzyl)malonate 11 . Crystallised from petrol-ethyl acetate mixture as colourless needles (2.50 g) in 73% yield, mp 1 13°C; ElMS rnIz (% reI. int.): 343([M+2t) (2), 341�) (4), 282( 1 5), 268(7), 226(29), 1 92( 14), 1 74(43), 1 52(1 8), 125(40), 1 02(80), 83( 12) and 43(1 00); CIMS m1z (% reI. int.): 342([M+ 1 n ( 1 00), 296( 1 0), 282(25), 226(20), 1 74( 1 9), 146( 10), 125( 1 5) and 43(8); IH NMR (250 MHz) : 0 · 1 .29(t, J = 7. 1 Hz, 6H, 2 x CH2CH3), 2.04(s, 3R, CH3CO), 3 .63(s, 2H, C-3H), 4.27(q, J = 7. 1 Hz, 4H, 2 x OCHz), 6.56(s, I H, NH),

6.98(m, I H, C-5'H), 7. 1 8( I H, brs, C-2'H) and 7.2 1(2H, m, C-4'H and C-6'H); I3C NMR (62.5 MHz) : 0 1 3 .95(2 x CH2CH3), 22.94(CH3CO), 37.36(C-3), 62.74(2 x OCH2), 67.00(C-2), 127.33, 1 27.96, 129.48 and 129.99(C-2', C-4', C-5' and C-6'), 1 34.05 and 1 37.30(C- l ' and C-3'), and 1 67.2 1 .and 1 69. 1 2(3 x CO); lR: 3300, 3050, 1 755, 1650, 1 520, 1 450, 1 380, 1 320, 1 3 1 0, 1280, 1 1 80, 1090, 1070, 1 050, 1 0 1 0, 950, 850 and 780 cm'l; UV: 222, 260 and 267 nm.

X-ray crystallography. The crystallographic measurements on monoethyl ester of a­acetamidomalonic acid 1, diethyl a-acetamido, a-( 4-trifluoromethylbenzyl)malonate 9 and diethyl a­acetamido, a-(3-chlorobenzyl)malonate 1 1 were made using either a Siemens P3R3 four-circle diffractometer or a Siemens SMART area-detector

. diffractometer. Graphite monochromated MO-Ka radiation was used in all cases. The structures were solved using SHELXTL-PLUSI9 and refined with SHELXL-9620. The crystal data of compounds 1, 9 and 11 are given below.

Compound 1 : C7HI INOs, M = 1 89. 1 7, T = 1 80(2)K, A = 0.7 1 073 A. Monoclinic a = 1 6.736 1(3), b = 8.8284(2), c = 14.22090( 10)A, f3 = 123 .96 1 0°, V = 1 742. 76(5)N, space group C2/c, Z = 8, Dx = 1 .442 Mg/m3, Jl = 0. 124 mm'I, F(OOO) = 800. Crystal size 0.40 x 0.36 x 0.22 mm; e range for data collection 2.73 - 28.39°; index ranges -2 1 < h < 16, -1 1 < k < 10, - 1 5 < I < 1 8; reflections collected 5045; independent reflections 2037 [R(int) = 0.0245]; refinement method full-matrix least squares on F2; data/restraints/parameters 2037/011 28; goodness-of-fit on F2 1 .084; R(F) [1 > 2 0' (I)] = 0.0368, wR2 = 0.0978; largest diff. peak and hole 0.287 anEl -0.256eA,3 .

Compound 9: CI7H20F3NOs, M = 375.34, T = 220(2)K, A = 0.71 073A; Monoclinic a = 1 8.9890( 1 1 ), b = 1 0.5934(6), c = 9.4289(5) A, f3 = 92.90°, V = 1 894.3(2)N, space group P21/c, Z = 4., Dx = 1 .3 1 6 Mg/m3, Jl = 0. 1 1 5 mm'I, F(OOO) = 784. Crystal size 0.35 x 0.22 x 0. 1 0 mm; e range for data collection 1 .07-23 .27°, index ranges -2 1 < h < 20, - 1 1 < k < 10, - 10 < 1 < 1 0; reflections collected 8000; independent reflections 2728[R(int) = 0 . 1 1 77]; refinement method full-matrix least squares on F2; data/restraints/para­meters 271 8/9/243; goodness-of-fit on F2 1 . 1 33 ; R(F)

SINGH et aJ. : STUDIES ON PROClURAL NON-PROTEINOGENIC AMINO ACIDS 15

[I > 2 a(I)] = 0.08 1 1 , WR2 = 0.1 794; largest diff. peak and hole 0.498 and -0.309 eA-3•

Compound 11: CI6H2oClNOs, M = 341 .78, T = 1 80(2)K, A. = 0.7 1073A. Monoclinic a = 16.9999(8), b = 10.9594(4), c = 9.5076(4) A, B = 90.0160(1 0)°, V = 1 77 1 .35(13) A3, space group P2dc, Z = 4, Dx = 1 .282 Mglm3, J.1 = 0.239 nun-I, F(OOO) = 720. Crystal size 0.40 x 0.40 x 0.20 mm; e range for data collection 2.21 -25.00°; index rartges -22 < h < 22, -9 < k < 14, - 12 < I < 1 1 ; reflections collected 8471 ; independent reflections 3 1 04 [R(int) . = 0. 1884];

refinement method full-matrix least-squares on F2; datalrestraintslpara-meters 3 104/0/21 2; goodness-of­frt on F2

0.735; R(F) [I > 2 a (I)] = 0.0700, WR2 = 0.12�; largest diff. peak and hole 0.405 and -0.572 A-3 e .

Acknowledgement We thank the DST, New Delhi, India for the grant

of funds under the OST -RAS IL TP Programme. One of the authors (AS) th;mks the CSIR, New Delhi for financial assistance.

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