Manoyl-Oxide Biotransformations with Filamentous Fungi

Abstract

Microbial transformations of manoyl oxides by filamentous fungi have been used to introduce hydroxyl groups, regio- and stereoselectively, into substrates at positions difficult to achieve by chemical means. The principal objective of most papers published in this field has been to produce new, highly oxygenated, bioactive manoyl-oxide compounds that present a large diversity of biological properties. The manoyl oxides most frequently studied at present are forskolin and its derivatives, the pharmacological activity of which is related to their ability to activate AC (adenylate cyclase), thus generating an increase in intracellular cAMP (cyclic adenosine monophosphate). The microbial hydroxylation of forskolin and 1,9-dideoxyforskolin has been extensively studied, using the fungi Scopuloriopsis sp., Syncephalastrum sp., Neurospora crassa, Mortierella isabellina and several Aspergillus sp.. Other biotransformation studies of natural manoyl oxides and hemi-synthetic enantio derivatives, carried out via the biomimetic cyclization of ent-8α-hydroxylabda-13(16),14- dienes, have used filamentous fungi Curvularia lunata, Cunninghamella elegans, Fusarium moniliforme, Gibberella fujikuroi, Gliocladium roseum, Mucor plumbeus, Rhizopus nigricans and Neurospora crassa. In some cases, the new hydroxylations were introduced at the same positions as in natural forskolin, yielding some noteworthy products that show biological activities.