18 マイシノライドの合成研究

抄録

Micromonospora griseorubida sp. nov. produces a group of sixteen-membered macrolide antibiotics which are named mycinamicin I-V and protomycinolide (1). Synthetic studies on 1 and the aglycone (2) of mycinamicin V were undertaken by using the asymmetric epoxidation of allylic alcohol as the key step. meso-2,4-Dimethylglutaric anhydride (3) was transformed into the allyl alcohol (6) by a conventional way. Ti-catalysed epoxidation of (6) with TBHP in the presence of (+)-DIPT gave 7, as a 1:1 mixture of two diastereomers, optical purity of each being determined to be >95% ee after separation of a portion through a Lobar column. Regiospecific reduction of the mixture (7) by Red-al, followed by successive acetylation, deprotection, oxidation, and hydrolysis gave a mixture of lactone alcohols (10). 10 was then converted into the ester (14) which was separated from the undesired isomer, and further transformed into an ylide (16), as a common intermediate for C_1-C_<10> part (segment A) of 1 and 2. The lactone alcohol (10) was also transformed into (+)-Prelog-Djerassi lactonic methyl ester in two steps (overall 18% from 3). The C_<11>-C_<15> segments (22 and 27) for 1 and 2 (segment B's) were constructed as shown in the sequences 17→22 and 23→27, respectively, again taking advantage of the above epoxidation. Condensation of the segment A with the segment B's and subsequent steps leading to 1 and 2 are now in progress.