Explorations into neolignan biosynthesis: concise total syntheses of helicterin B, helisorin, and helisterculin A
Scott A Snyder1, Ferenc Kontes
1Department of Chemistry, Columbia University, Havemeyer Hall, 3000 Broadway, New York, New York 10027, USA.
Abstract:
Helicterins A and B (1 and 2), helisorin (3), and helisterculin A (4) are structurally unique natural products with the ability to combat the avian myeloblastosis virus. Biogenetically, their architectures are considered to be products of seemingly straightforward Diels-Alder, radical-based, or acid-induced dimerizations of common, simpler precursors. Yet, the pursuit of such blueprints in the laboratory has failed thus far in enabling their successful synthesis. Herein, we describe the first total syntheses of three of these natural products. Key features include the use of a building block distinct from Nature's likely starting material, highly complex retro Diels-Alder/Diels-Alder reaction cascades, an unconventional protecting group to achieve the proper balance of chemical reactivity on sensitive scaffolds, and several carefully developed reaction conditions that effectively balance competing reaction pathways.
Related Concept Videos
02:17Reduction of Alkenes: Asymmetric Catalytic Hydrogenation
The metal catalyst used can be either heterogeneous or homogeneous. When hydrogenation of an alkene generates a chiral center, a pair of enantiomeric products is expected to form. However, an enantiomeric excess of one of the products can be facilitated using an enantioselective reaction or an...
01:29Biosynthesis of Lipids
01:32Aldehydes and Ketones with HCN: Cyanohydrin Formation Overview
02:34Preparation of Alkynes: Dehydrohalogenation
Alkynes can be prepared by dehydrohalogenation of vicinal or geminal dihalides in the presence of a strong base like sodium amide in liquid ammonia. The reaction proceeds with the loss of two equivalents of hydrogen halide (HX) via two successive E2 elimination reactions.
02:24Reduction of Alkynes to cis-Alkenes: Catalytic Hydrogenation
Like alkenes, alkynes can be reduced to alkanes in the presence of transition metal catalysts such as Pt, Pd, or Ni. The reaction involves two sequential syn additions of hydrogen via a cis-alkene intermediate.
01:28Biosynthesis of Nucleic Acids