Brønsted Acid-Mediated Conversion of Naturally Abundant Lathyrane Diterpenes: Are Rare 10,11-seco-Lathyrane Diterpenes Artifacts?

The question of whether rare 10,11-seco-lathyranes are natural products or artifacts is thoughtfully considered after a Brønsted acid-mediated chemical conversion of naturally abundant 5/11/3 lathyrane type diterpenes into 10,11-seco-lathyranes was developed. Benefiting from this concise route, a series of 10,11-seco-lathyrane products (1-14) were smoothly synthesized. The conversion may involve an acid promoted cyclopropane ring opening accompanied by a double bond shift with final trapping of carbocation. The ease of this chemical conversion under mildly acidic conditions may imply that the 10,11-seco-lathyranes isolated to date are artifacts. This work not only develops a new modular synthetic strategy for efficient constructing rare 10,11-seco-lathyranes, but also provides a promising bioactive diterpene with excellent effect against the NO production on LPS-induced BV-2 cells.