Practical Formal Total Syntheses of the Homocamptothecin Derivative and Anticancer Agent Diflomotecan via Asymmetric Acetate Aldol Additions to Pyridine Ketone Substrates
作者:René Peters、Martin Althaus、Christian Diolez、Alain Rolland、Eric Manginot、Marc Veyrat
DOI:10.1021/jo060928v
日期:2006.9.1
scalable asymmetric routes to DE ring fragment 7, a key building block in the synthesis of the homocamptothecin derivative diflomotecan 4, are described. The “acetal route” starts from 2-chloro-4-cyanopyridine 8 and represents an enantioselective and optimized modification of the original racemic discovery chemistry synthesis. The inefficient optical resolution procedure was replaced by an efficient asymmetric
描述了两种实际,有效且可扩展的至DE环片段7的不对称路线,DE环片段7是高喜树碱衍生物双氟醚4合成中的关键组成部分。“缩醛途径”始于2-氯-4-氰基吡啶8,代表对映体选择性和对原始外消旋发现化学合成的优化修饰。低效率的光学拆分程序被高效的不对称乙酸酯醛醇加成剂(dr 87:13)取代到酮基质上,这是生成具有高立体选择性的(R)-构型四元立体中心的关键步骤。7最终,在九个步骤中以8.9%的总收率(er 99.95:0.05)获得了目标产物,从而避免了色谱纯化,并且与初始操作相比具有优势。在从2-氯异烟酸酸41开始的相关“酰胺途径”中,使用仲酰胺指导基团来促进吡啶3-位的邻位锂化。该方案的关键步骤再次包括实际的不对称乙酸羟醛加成(dr = 87:13)。因此,在九个步骤中,仅需进行一次色谱纯化,即可以11.1%的总收率(er> 99.95:0.05)获得DE环结构单元7。