Highly stereoselective synthesis of methynolide, the aglycone of the 12-membered ring macrolide methymycin, from D-glucose
作者:Yuji Oikawa、Tatsuyoshi Tanaka、Osamu Yonemitsu
DOI:10.1016/s0040-4039(00)84871-6
日期:1986.1
A highly stereoselective and efficient synthesis of methynolide, the aglycone of 12-membered macrolide methymycin, was achieved from of C1–C8 and C9–C13 segments synthesized from D-glucose by employing some stereoselective reactions and benzyl-type protectinggroups.
based on Cram chelation control. Ring-closing metathesis, as the key reaction, was carried out to combine the segments for the synthesis of methynolide and 10-epi-methynolide. The total synthesis of methymycin was also achieved by the glycosylation of methynolide with the trichloroimidate derivative of D-desosamine.
Highly stereoselective total synthesis of methynolide, the aglycon of the 12-membered macrolide antibiotic methymycin. III. An efficient synthesis of methynolide.
Methynolide (1), the aglycon of the 12-membered macrolide antibiotic methymycin, was synthesized highly stereoselectively and efficiently from D-glucose via two segments i (3 : C-9-C-13) and ii (4 : C-1-C-8). Esterification of the two segments proceeded smoothly by Yamaguchi's method. When the resulting ester (10) was treated with potassium carbonate in toluene in the presence of 18-crown-6 at 80 °C under Nicolaou's conditions, the intramolecular Wittig-Horner reaction occurred very smoothly, and the 12-membered cyclic enone (11) was isolated in excellent yield. Finally, silyl and benzyl protecting groups were removed with fluoride anion and 2, 3-dichloro-5, 6-dicyanobenzoquinone, respectively, to afford methynolide (1) in excellent yield. The overall stereoselectivity for the construction of four new chiral centers was very high (89%).
Degradation experiments are described which establish rigorously structure (II) for neomethymycin (C25H43NO7). This antibiotic belongs, therefore, to the macrolide group and differs from methymycin (I) only in the location of one hydroxyl group, which results in marked changes in chemical behavior. The two antibiotics appear to have the same absolute configuration at the relevant asymmetric centers
描述了降解实验,其严格建立了新甲霉素(C 25 H 43 NO 7)的结构(II )。因此,该抗生素属于大环内酯类,仅在一个羟基的位置上与甲基霉素(I)不同,这导致化学行为发生明显变化。两种抗生素在相关的不对称中心处似乎具有相同的绝对构型,如通过常见降解产物的分离和某些旋转分散曲线的总体相似性推断的那样。从生物遗传学的角度来看,新甲霉素中C-12处的羟基位置值得注意。
Ditrich, Klaus, Liebigs Annalen der Chemie, 1990, # 8, p. 789 - 793