Cancer is one of the leading causes of death worldwide. If recent trends are to be followed, by 2030, there will be a 68% increase in a number of cases than in 2012 with a staggering number of up to 23.6 million. Hapalindoles are arguably the largest and most comprehensive sub-class of indole alkaloids isolated from secondary metabolites released by cyanobacteria<i>.</i> Over the years they were found to be having potent anticancer activity against a wide range of cancer cells such as human HT-29 (colon adenocarcinoma), MCF-7 (breast), NCI-H460 (large cell lungs) and SF268 (glioblastoma). They also exhibit a wide array of biological activities such as antimicrobial, insecticidal, antialgal, phytotoxic, and antimycotic etc. Keeping this biological importance along with structural complexity in mind, a stereoselective, redox-neutral, Brønsted acid-catalyzed cascade Prins-type cyclization between indole and aldehyde is described to access several structurally diverse indole terpenoid scaffolds in a single step. Applying this concept, a stereo-divergent total synthesis of nine hapalindole type alkaloids are accomplished. Key transformations include allylation using geometrically isomeric allylboronic acid followed by a <i>p</i>-toluenesulfonic acid mediated deprotection-cyclization cascade.

Stereodivergent total synthesis of hapalindoles, fischerindoles, hapalonamide H, and ambiguine H alkaloids by developing a biomimetic, redox-neutral, cascade Prins-type cyclization

2019 Spring National Meeting

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