Structure and Computational Basis for Backbone Rearrangement in Marine Oxasqualenoids

Six novel oxasqualenoids (polyether triterpenes) were isolated from the red alga Laurencia viridis. Laurokanols A−E (1−5) comprise an unreported tricyclic core with a [6,6]- spiroketal system. Yucatecone (6) shows a biogenetically intriguing epimerization at C14. Quantum mechanical calculations were used to corroborate their structures and to explain key steps involved in the biogenetic mechanisms proposed for the formation of oxasqualenoids.