Revisiting synthetic preparation of the quorum sensing substrate S-d-ribosyl-l-homocysteine (SRH)

•We synthesize S-ribosylhomocystine (SRH) at convenient scale.•Thioether generation by substitution is influenced by both base and electrophile.•Single-step global deprotection efficiently accesses the final product.•A straightforward purification process isolates SRH·TFA at high purity.•The final SRH·TFA product serves as substrate in the LuxS bioassay.

Cleavage of the thioether bond of S-d-ribosyl-l-homocysteine (SRH) by the enzyme S-ribosylhomocysteinase (LuxS) serves as the final biosynthetic step in the generation of the quorum sensing autoinducer AI-2 by bacteria. Herein, a revised chemical synthesis of SRH is presented at convenient scale and purity for in vitro studies of LuxS. Potassium bis(trimethylsilyl)amide (KHMDS) is identified as a judicious base for the formation of the thioether of the target compound from readily-accessible precursors: a thiol nucleophile derived from l-homocystine and a sulfonate-activated d-ribosyl electrophile. The exclusive use of acid-labile protecting groups allows for facile deprotection to the final product, producing the TFA salt of SRH in five synthetic steps and 26% overall yield. The chemically-synthesized material is isolated at high purity and demonstrated to serve as the LuxS substrate by an in vitro assay.

Graphical abstractFigure optionsDownload full-size imageDownload as PowerPoint slide