Wednesday, June 17, 2015

An Excellent Overview of the [Bio]Synthesis and Bioactivity of ent-Kaurene Diterpenoids

            The ent-kaurene class of natural products are diterpenoids that are formed as secondary metabolites in higher plants of the genus Stevia and Isodon. Steviol diterpenoids and glycosides thereof accumulate in the leaves of Stevia rabaudiana at high concentrations and the plant extracts are marketed as ‘Stevia,’ a natural low-calorie sweetener. At this site, we’ve discussed Stevia’s prominent role in a key plot point on the show Breaking Bad. We’ve also covered synthetic aspects related to cafestol, an ent-kaurene diterpenoid found in coffee drinks. Now Corinna Schindler’s group at the University of Michigan has contributed an outstanding Review Article in the journal Tetrahedron that presents an authoritative overview of ent-kaurene isolation, biosynthesis, antibacterial and antitumor activity. The manuscript also provides a comprehensive account of synthetic strategies (dating back to Bob Ireland’s work in 1966!) used access ent-kaurene diterpenoids in a laboratory setting. Prior to reading this Review, I’ll admit that I was not aware of (and could not find in the scientific literature…not for a lack of searching) the reason for adding the ‘ent-’ prefix to the ‘ent-kaurene’ natural products. Schindler et al clear that up in two sentences:

“In 1999, kaurene was classified as the fundamental parent structure of this subclass of diterpenoids by the IUPAC. Despite this nomenclature, the vast majority of kaurene diterpenoids isolated to date belong to the ent-kaurenes, in which all asymmetric centers undergo configurational inversion…”


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