Abstract
The recent findings1_??_3) that prenylmercaptan (3-methyl-2-butene-l-thiol) is the major component of the sunlight flavor of beer has led us to investigate the pathway of its evolu-tion. S-Prenyl-L-cysteine, S-(3-methyl-2-butenyl)-L-cysteine, was synthesized according to the general outline of A. Stoll et al.4) from L-cyteine and prenylbromide, since it was considered as one of the precursors of the sunlight flavor of beer. S-Prenyl-L-cysteine was a colorless and odorless crystal, but this compound generated prenylmercaptan when the aqueous solution was exposed to sunlight. The addition of a small amount of riboflavin to the solution as a photosensitizer increased the mercaptan evolution. Prenylmercaptan formed by sun-light was isolated as its 2, 4-dinitrophenyl derivative and identified by the comparison of melting point, chromatographic behavior and infrared spectrum with an authentic sample and by its elemental analysis.
