Terpenoids bearing the 7-oxabicyclo[2.2.1]heptane (7-oxanorbornane) skeleton. Natural sources, biological activities and chemical synthesis

Abstract

Compounds bearing the 7-oxabicyclo[2.2.1]heptane (7-oxanorbornane) subunits have been used extensively in the synthesis of a large array of complex organic structures. The ease of synthesis of compounds having this substructure in enantiomerically pure form, using Diels-Alder chemistry, is today an almost routinely experimental work. Moreover, the reactivity of these compounds, easily controllable and almost always associated to its ring-strain, makes them particularly valuable chiral building blocks. However, the presence of compounds showing this bicyclic skeleton in Nature has attracted less attention despite its relatively broad distribution. Many of these compounds have been shown to possess important biological activities presenting, in cases, unprecedented biogenetic origin. In addition, some of them have been considered as convenient synthetic targets enabling the development of new synthetic methodologies. In this article we have reviewed different families of terpenoids having in its structure this bicyclic subunit, paying particular attention to their natural sources, biosynthesis, biological activity and chemical synthesis.