31 抗腫瘍抗生物質オキサゾロマイシン類の立体制御合成 : ネオオキサゾロマイシンの形式合成(口頭発表の部)

抄録

Oxazolomycin and neooxazolomycin are structurally closely related antibiotics isolated from Streptomyces sp. by Uemura et al. The former is the parent member of a class of polyene bicyclic antibiotics, other members being oxazolomycin B and C, 16-methyloxazolomycin, and curromycin A and B. The oxazolomycins were found to exhibit wide ranging and potent antibiotic activity, including inhibitory activity against Gram-positive bacteria, antiviral activity against vaccina, herpes simplex type I and influenza A, as well as in vivo antitumor activity. The intriguing molecular architectures and the biological activities make these compounds attractive targets for synthesis. However, the total synthesis is limited to Kende's synthesis of neooxazolomycin. We report here a novel approach to neooxazolomycin, which can be also applicable to the synthesis of oxazolomycin. Our synthesis of right hand core 22 started with methyl (S)-hydroxyisobutyrate and proceeded through three major transformations involving regio- and stereoselective iodination via intramolecular Pt-catalyzed hydrosilylation, Pd-catalyzed enolate alkenylation, and stereoselective dihydroxylation accompanied by concomitant lactonization. Nozaki-Hiyama-Kishi coupling of aldehyde 23 obtained from 22 with N-Fmoc-iododienamine 24 gave 7S-isomer 25 and 7R-isomer 26 as a 1: 1 epimeric mixture. It was gratifyingly found that Dess-Martin oxidation of this epimeric mixture followed by L-Selectride reduction of the resulting ketone produced the desired 7R-isomer 26 in excellent stereoselectivity (94% de). Removal of the silyl protecting group allowed us to obtain the Kende's intermediate 27, the synthesis of which constitutes a formal synthesis of neooxazolomycin.