V. I. Maleev

Improved procedures for the synthesis of (S)-2-[N-(N′-benzylprolyl)amino]benzophenone (BPB) and Ni(II) complexes of Schiff's bases derived from BPB and amino acids

(S)-N-Benzylproline (BP) was obtained by the reaction of (S)-proline and benzylchloride in high chemical yield (89%). (S)-2-[N-(N′-Benzylprolyl)amino]benzophenone (BPB) was synthesized in amounts greater than 100 g by the SOCl2 promoted condensation of BP with 2-aminobenzophenone (yield 82%). Ni(II) complexes of Schiffs bases derived from BPB and amino acids were prepared by an improved procedure involving the use of KOH as a base and MeOH as solvent (yield 90–91%).

Anionic chiral cobalt(III) complexes as catalysts of asymmetric synthesis of cyanohydrins

Chiral coordinatively saturated cobalt(III) complexes with Schiff bases of enantio-pure amino acids are formed as Λ and Δ-isomers, which are not transformed into each other under normal conditions. These complexes catalyze the formation of enantiomerically enriched cyanohydrins from aldehydes and Me3SiCN under homo-and heterogeneous catalysis.

Equilibrium ch acidity of Ni(II) complexes of Schiff's bases of amino acids with S-2-N-(N′-benzylprolyl)amino-benzaldehyde and S-2-N-(N′-benzylprolyl)aminobenzophenone

Summary1.By metal exchange in DMSO (K+ cation) pK values have been measured for a series of acids which are Ni(II) complexes of Schiffs bases of the amino acids Gly, S-Ala, and S-Val, with S-2-N-(N′-benzylprolyl)arainobenzaldehyde and S-2-N-(N′-benzylprolyl)aminobenzo-phenone.2.The amino acid fragment in the studied Ni(II) complexes possesses high acidity close to fluorene but five orders of magnitude greater than for acetophenone and approaching nitroalkanes in acidity.

Tetraaryl-1,3-dioxolane-4,5-dimethanols as catalysts for the addition of trimethylsilyl cyanide to benzaldehyde and the oxirane ring

The synthesis of 1,2-, 1,3-, and 1,4-phenylene-bis[(4R,5R)-4,5-di(hydroxydiphenylmethyl)-1,3-dioxolane]s (ortho-, meta-, and para-bis-(R,R)-TADDOLs) and bis[4-{[(4R, 5R)-4,5-di(hydroxydiphenylmethyl)]-1,3-dioxolan-2-yl}phenyl]methane was carried out. The possibilities of the use of these compounds as catalysts for the C-C bond formation in the addition of Me3SiCN to benzaldehyde and the oxirane ring opening in cyclohexene oxide by Me3SiCN were investigated. The catalytic activity of different bis-(R, R)-TADDOLs in this series depends on their structure.

Transition metal complexes — A new class of catalysts of interfacial alkylation for the asymmetrical synthesis of α-amino acids

A new class of catalysts of interfacial asymmetrical alkylation is suggested for the synthesis of α-amino acids — positively charged complexes of the transition metals Cu(II), Ni(II), and Pd(II). These complexes consist of several fragments, by variation of which the structure of the catalysts can readily be modified. The complexes are chiral on account of (S)proline derivatives contained in them as one of the fragments. The catalyst complexes (C) were used in the alkylation of amino acid fragments of Ni(II) complexes of the Schiff base of glycine with N-(2-pyridinecarbonyl)-o-aminobenzophenone (Ni-PBP-Gly) and the Schiff base of alanine with N-(2-pyridinecarbonyl)-o-aminobenzaldehyde (Ni-PBA-Ala) under interfacial conditions. After decomposition of the alkylated complexes, phenylalanine and α-methyl-phenylalanine were isolated with yields of 33–87% and optical purity (o.p.) from 3 to 21%, depending on the C used.

Asymmetric synthesis of threonine and retroracemization of amino acids using Ni(II) complexes of Schiff bases with S-2-n-(N′-benzylprolyl)aminobenzaldehyde

Conclusions1.Complexes of Ni(II) with Schiff bases of 2-N-(2′-S-N-benzylpyrrolidin-2-carbonyl)aminobenzaldehyde (S-BPaB) with glycine and valine have been synthesized in which the Ni ion is coordinated with the N atoms of the proline fragment, of the aldimine group, of the ionized amide, and with the carboxyl group.2.The presence has been shown of enantioselective effects in complexes of Schiff bases of S-BPAB with R,S-amino acids with Ni(II) which increase with an increase in volume of the amino acid side chain. The enantiomer excess for the complex with S-Val was 78%.3.The retroracemization of alanine, valine, norvaline, phenylalanine, phenylglycine, and tryptophan was carried out using S-BPAB and Ni(II) with enantiomer yields of 15, 78, 42, 40, 39, and 64% respectively.4.The asymmetric synthesis of S-threonine has been effected by condensing acetaldehyde with (S-BPAB-Gly)·Ni(II) on catalysis with Et3N with a S-Thr and S-allo-Thr ratio of 1∶2 and enantiomer yield of 86 and 76% respectively. An increase in pH led to a reduction in enantiomer yield and reversal of the sign of the enantioselective effect.5.A method has been developed for enantiomer analysis of tryptophan using high-pressure liquid chromatography as has a GLC method for difficult amino acids using a high-temperature chiral chromatographic phase, viz., N-heptadecanoyl-S-Val tert-butylamide.

Asymmetric synthesis of aspartic and α-methylaspartic acids via Ni(II) complexes with schiff bases of glycine and alanine and chiral carbonyl-containing reagents

We propose a method for the synthesis of aspartic and α-methylaspartic acids by alkylation with ethyl bromoacetate of the α-carbon atom of the amino acid moiety in Ni(II) complexes of Schiff bases of glycine with (S)-2-[(N-benzylprolyl)amino]benzophenone and alanine with (S)-2-[(N-benzylprolyl)amino]-benzaldehyde, respectively. Attempts to synthesize α-methylaspartic acid by oxidative cleavage of the C=C bond to a COOH group in the complex of the Schiff base of α-allylalanine with (S)-2-[(N-benzylprolyl)amino]benzophenone were unsuccessful.

Synthesis of optically active amino acids during asymmetric phase-transfer catalysis

ConclusionsAsymmetric alkylation of the amino acid fragment of Ni2+ complexes of the Schiff bases of glycine with N-(2-pyridinecarbonyl)-o-aminobenzophenone and of alanine with N-(2-pyridinecarbonyl)-o-aminobenzaldehyde has been carried out under phase-transfer conditions using N-benzylcinchonidinium chloride as the chiral phase-transfer catalyst.