Synthesis and Absolute Configuration of Wybutine, the Fluorescent Minor Base from Phenylalanine Transfer Ribonucleic Acids.
作者:Taisuke ITAYA、Akemi MIZUTANI、Takehiko IIDA
DOI:10.1248/cpb.39.1407
日期:——
The phosphonium chloride 6 having an optically active amino acid moiety was synthesized from (S)-serine benzylester tosylate (2b) through a six-step route. The utility of 6 as a reagent for the Witting reaction was exemplified in the olefination with benzaldehyde, affording the (E)-β, γ-unsaturated amino acid derivative 11 as a sole geometrical ispmer. This new method of amino acid homologation was successuflly employed for the first chiral synthesis of wybutine (1c), the minor base isolated from yeast phenylalanine transfer ribonucleic acids : the Wittig reaction between 6 and the tricyclic aldehyde 16 followed successively by methylation and catalytic reduction afforded 1c. Comparison of wybutine with synthetic 1c has unequivocally established that wybutine has an S configuration.
(R)-[2-Carboxy-2-[(methoxycarbonyl)amino]ethyl]triphenylphosphonium chloride (1) was converted by treatment with anion exchange resin (HCO-3) into the inner salt 13h, which gave a better yield (43%) than 1 in the Wittig reaction with benzaldehyde to afford the [S-(E)]-(2-phenylvinyl)glycine derivative 24. The inner salt 13i bearing an N-benzyloxycarbonyl group was prepared by hydrogenolysis of (R)-[3-benzyloxy-2-[(benzyloxycarbonyl)amino]-3-oxopropyl]triphenylphosphonium chloride (11e) over palladium on carbon, followed by dehydrochlorination. Hydrogenolysis of 11e over Pearlman's catalyst afforded the unprotected phosphonium chloride 12 (X=Cl). N-tert-Butoxycarbonylation of 12 followed by dehydrochlorination afforded 13j, which was more efficiently prepared through hydrogenolysis of (R)-[3-benzyloxy-2-[(tert-butoxycarbonyl)amino]-3-oxopropyl]triphenylphosphonium chloride (11f).The usefulness of 13h-j as building blocks for the synthesis of configurationally labile (2-arylvinyl)glycine derivatives was exemplified by the Wittig reactions with piperonal, which exclusively afforded the (E)-isomers 18h-j with high optical purity in 28-39% yield.