Gram-positive bacteria of the genus Streptomyces are industrially important microorganisms, producing >70% of commercially important antibiotics. The production of these compounds is often regulated by low-molecular-weight bacterial hormones called autoregulators. Although 60% of Streptomyces strains may use γ-butyrolactone–type molecules as autoregulators and some use furan-type molecules, little is known about the signaling molecules used to regulate antibiotic production in many other members of this genus. Here, we purified a signaling molecule (avenolide) from Streptomyces avermitilis —the producer of the important anthelmintic agent avermectin with annual world sales of $850 million—and determined its structure, including stereochemistry, by spectroscopic analysis and chemical synthesis as (4 S ,10 R )-10-hydroxy-10-methyl-9-oxo-dodec-2-en-1,4-olide, a class of Streptomyces autoregulator. Avenolide is essential for eliciting avermectin production and is effective at nanomolar concentrations with a minimum effective concentration of 4 nM. The aco gene of S. avermitilis, which encodes an acyl-CoA oxidase, is required for avenolide biosynthesis, and homologs are also present in Streptomyces fradiae , Streptomyces ghanaensis , and Streptomyces griseoauranticus , suggesting that butenolide-type autoregulators may represent a widespread and another class of Streptomyces autoregulator involved in regulating antibiotic production.

Mining of bacterial genome data has revealed numerous presumptive terpene synthases. Heterologous expression of several putative terpene synthase genes in an engineered Streptomyces host has revealed 13 newly discovered terpenes whose GC-MS and NMR data did not match any known compounds in the spectroscopic databases. Each of the genes encoding the corresponding terpene synthases were silent in their parent microorganisms. Heterologous expression and detailed NMR spectroscopic analysis allowed assignment of the structures of 13 new cyclic terpenes. Among these newly identified compounds, two were found to be linear triquinane sesquiterpenes that have never previously been isolated from bacteria or any other source. The remaining 11 new compounds were shown to be diterpene hydrocarbons and alcohol, including hydropyrene (1), hydropyrenol (2), tsukubadiene (11), and odyverdienes A (12) and B (13) each displaying a novel diterpene skeleton that had not previously been reported.

A total synthesis of the novel neurotrophic agent (+)-lactacystin (1) has been achieved in 11 steps and 14% overall yield from (2R,3S)-3-hydroxyleucine [(+)-16]. The construction and bioassay of several active analogs are also described. A new asymmetric approach furnished the four stereoisomers of 3-hydroxyleucine, as required starting materials in high overall yield and enantiomeric purity.

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