Mass spectrometry-guided discovery of new analogs of bicyclic phosphotriester salinipostin and evaluation of their monoacylglycerol lipase inhibitory activity.

Natural products containing the highly unusual phosphotriester ring are known to be potent serine hydrolase inhibitors. The long-chain bicyclic enol-phosphotriester salinipostins (SPTs) from the marine actinomycete Salinispora have been identified as selective antimalarial agents. A potential regulatory function has been suggested for phosphotriesters based on their structural relationship with actinomycete signaling molecules and the prevalence of spt-like biosynthetic gene clusters across actinomycetes. In this study, we established a mass spectrometry-guided screening method for phosphotriesters focusing on their characteristic fragment ions. Applying this screening method to the SPT producer Salinispora tropica CNB-440, new SPT analogs (4-6) were discovered and their structures were elucidated by spectroscopic analyses. Previously known and herein-identified SPT analogs inhibited the activity of human monoacylglycerol lipase (MAGL), a key serine hydrolase in the endocannabinoid system, in the nanomolar range. Our method could be applied to the screening of phosphotriesters, potential serine hydrolase inhibitors and signaling molecules.