Department of Chemistry, The University of Kansas , Lawrence, Kansas 66045, United States.
J Org Chem. 2017 Dec 1;82(23):12257-12266. doi: 10.1021/acs.joc.7b02101. Epub 2017 Nov 17.
The pentacyclic alkaloid calothrixin B (1) has been synthesized in 5 steps from murrayaquinone A (9). The key step involved the union of boryl aniline 31 with brominated murrayaquinone A (26). In this transformation, alkylquinone 26 undergoes tautomerization to a quinone methide, which is intercepted by boryl aniline 31 to forge a new C-N bond. An intramolecular Suzuki coupling, followed by dehydrogenative aromatization, completed the synthesis of calothrixin B. Subsequent N-oxidation of calothrixin B delivered calothrixin A. The successful synthesis of these alkaloids and the challenges that led to the development of the final synthesis plan are reported herein.
从 murrayaquinone A（9）出发，经过 5 步反应合成了五环生物碱 calothrixin B（1）。关键步骤涉及到硼酸苯胺 31 与溴代 murrayaquinone A（26）的结合。在此转化中，烷基醌 26 经历互变异构化生成醌甲醚，硼酸苯胺 31 进攻醌甲醚生成新的 C-N 键。随后进行分子内 Suzuki 偶联和脱氢芳构化反应，完成了 calothrixin B 的合成。calothrixin B 的 N-氧化得到 calothrixin A。本文报道了这些生物碱的成功合成以及导致最终合成方案发展的挑战。
