Interphylal Product Splicing: The First Total Syntheses of Cephalostatin 1, the North Hemisphere of Ritterazine G, and the Highly Active Hybrid Analogue, Ritterostatin G<sub>N</sub>1<sub>N</sub><sup>1</sup>
作者:Thomas G. LaCour、Chuangxing Guo、Sudhakar Bhandaru、Michael R. Boyd、P. L. Fuchs
DOI:10.1021/ja972160p
日期:1998.2.1
Convergent total syntheses of the extremely potent cell growth inhibitor cephalostatin 1 and two hybrid analogues, ritterostatins G(N)1(N) and G(N)1(S), have been achieved. Ritterostatin G(N)1(N) displays sub-nanomolar activity in the 60 cell line human tumor panel of the National Cancer Institute. The North hemisphere of ritterazine G was efficiently constructed from hecogenin acetate in 15% yield over 13 steps. Extension of a key photolysis/Prins sequence to intermediates 19 and 32 proceeded in excellent yield, leading to installation of the Delta(14) moiety in the-North G-and South I steroidal subunits. Application of a method for directed unsymmetrical coupling furnished the natural and analogue pyrazines in good yield from the cephalostatin and ritterazine components.
Let′s get practical: A new practical synthetic strategy for natural sterols starting from pregnan‐(16S,20S)‐diols and steroid‐(16S),22‐lactones is presented. A tandem double oxymercuration–demercuration and a substitution–ketalization cascade are considered as the key reactions for the construction of the spiroketal rings.