Enantioselective approaches to the construction of four complex building blocks of the structurally intricate marine macrolide known as spongistatin 1 are presented. The first phase of the synthetic effort relies on a practical approach to a desymmetrized, enantiomerically pure spiroketal ring system incorporating rings A and B. Concurrently, the C17–C28 subunit, which houses one-fifth of the stereogenic centers of the target in the form of rings C and D, was assembled via a composite of stereocontrolled aldol condensations. Once arrival at the entire C1–C28 sector had been realized, routes were devised to provide two additional highly functionalized sectors consisting of C29–C44 and C38–C51. A series of subsequent transformations including cyclization of the E ring and hydroboration to afford the B-alkyl intermediate for the key Suzuki coupling to append the side chain took advantage of efficient stereocontrol. Ultimately, complete assembly and functionalization of the western EF sector of spongistatin was thwarted by an inoperative Suzuki coupling step intended to join the side chain to the C29–C44 sector, and later because of complications due to protecting groups, which precluded the complete elaboration of the late stage C29–C51 intermediate.
提出了构建结构复杂的海洋大环内酯素丝孢菌素1的四个复杂构建模块的对映选择性方法。合成工作的第一阶段依赖于一种实用方法,用于构建包含环A和B的非对称、对映纯的螺环糖环系统。同时,C17-C28亚单位,其中包含目标物中五分之一的立体中心,以环C和D的形式组装,通过立体控制的醛缩合反应组合而成。一旦完成整个C1-C28区段的合成,就设计了提供C29-C44和C38-C51两个额外高度官能化区段的路线。随后的一系列转化反应包括E环的环化和氢硼化反应,以获得用于关键的铃木偶联的B-烷基中间体,利用了高效的立体控制。最终,丝孢菌素的西部EF区段的完整组装和官能化受挫于无法进行的铃木偶联步骤,该步骤旨在将侧链连接到C29-C44区段,后来由于保护基的复杂性导致无法完全展开晚期C29-C51中间体。