Towards a sustainable generation of pseudopterosin-type bioactives†
Pseudopterosins (Ps), marine diterpene glycosides derived from the marine octocoral Antillogorgia elisabethae, have potent anti-inflammatory activity demonstrated in phase II clinical trials. As multi-step total chemical synthesis is not economical, Ps applications are limited to anti-irritant cosmeceuticals, which are exclusively sourced by unsustainable coral extraction. While chemical intermediates in Ps biosynthesis have been resolved, the underlying biochemical processes remain elusive. Therefore, a coral independent route to enable sustainable access to Ps and respective bioactive precusors is required. Here, in silico guided mutagenesis of the hydropyrene synthase (HpS) from Streptomyces clavuligerus reveals five unique, catalytically relevant methionine residues, and affords selective formation of biosynthetic Ps precursors isoelisabethatriene A and B in an Escherichia coli host with total terpene yield of HpS M75L of 41.91 ± 1.87 mg L−1. This is the first experimental precedence of methionine residues being involved in terpene synthase catalysis, indicating that HpS may belong to a new subfamily. Further, lipase catalysed chemo-enzymatic oxidation differentially transforms the isomers isoelisabethatriene A and B to the advanced Ps precursor erogorgiaene (yield: 69%) and the new compound 1R-epoxy-elisabetha-5,14-diene (EED) (yield: 41%), respectively. As erogorgiaene has significant activity against multi-drug resistant Mycobacterium tuberculosis, the process provides a consolidated and scalable access to erogorgiaene, which allows further clinical development of this compound. Moreover, erogorgiaene access also provides a consolidated route for Ps synthesis. Synergistically EED generation affords a new scaffold for Ps-type drug development. These technologies assist in preserving fragile coral reef ecosystem biodiversity and open a fast track for clinical Ps development.