Synthetic Studies on Actinobolin and Bactobolin: Synthesis of <i>N</i>-Desalanyl-<i>N</i>-[2-(trimethylsilyl)ethanesulfonyl] Derivatives from a Common Intermediate and Attempted Removal of the SES Protecting Group
作者:Dale E. Ward、Yuanzhu Gai、Brian F. Kaller
DOI:10.1021/jo960579c
日期:1996.1.1
Two closely related syntheses of 5,6-O-(2-propylidene)-N-desalanyl-N-2-(trimethylsilyl)ethane-sulfonyl]bactobolin (9b) from (+)-12, an intermediate previously prepared from D-glucose, are reported. In each case, the key step involves a precedented stereoselective addition of LiCHCl2 in the presence of CeCl3 to a suitably protected a-amino ketone, Intermediates from both synthetic routes to 9b can be prepared by degradation of actinobolin (2) thereby establishing a potential method for the transformation of actinobolin into bactobolin. An efficient route to 5,6-O-(2-propylidene)-N-desalanyl-N-[[2-(trimethylsily)ethanesulfonyl]actinbolin (7b) from (+)-12 involving an unexpected cyclization of 29 was discovered. The 2-(trimethylsilyl)ethanesulfonyl (SES) protecting group in 7b tvas removed by reaction with Bu(4)NF in wet THF. The nature of the Bu(4)NF reagent was found to be important to the outcome of the reaction. Several improvements over our previously reported synthesis of actinobolin from D-glucose are noted. Although precedented, the removal of the SES protecting group from 9b could not be achieved thereby preventing completion of a total synthesis of bactobolin.