Oxidation of N-methyl-3-(methylsulfanyl)aniline (I) using hydrogen peroxide in acetone gave the required sulfoxide along with some sulfone, which was removed by chromatography on silica gel. After conversion to the corresponding hydrochloride salt (II), its condensation with 2-chloro-5-(methylthio)phenyl cyanamide (III) in boiling toluene furnished guanidine (IV) (1). The racemic mixture of sulfoxides was finally resolved by chiral HPLC on a Chiralpak AD column to provide the title (R)-enantioner.

An asymmetric alternative synthesis has been reported, involving the chiral oxidation of sulfide (I) with (R)-(-)-(8,8-dichloro-10-camphorsulfonyl)oxaziridine (DCCSO) to the desired (R)-sulfoxide (V). Conversion to the hydrochloride salt, followed by condensation with cyanamide (III) afforded the title chiral compound.

Oxidation of N-methyl-3-(methylsulfanyl)aniline (I) using hydrogen peroxide in acetone gave the required sulfoxide along with some sulfone, which was removed by chromatography on silica gel. After conversion to the corresponding hydrochloride salt (II), its condensation with 2-chloro-5-(methylthio)phenyl cyanamide (III) in boiling toluene furnished guanidine (IV) (1). The racemic mixture of sulfoxides was finally resolved by chiral HPLC on a Chiralpak AD column to provide the title (R)-enantioner.

An asymmetric alternative synthesis has been reported, involving the chiral oxidation of sulfide (I) with (R)-(-)-(8,8-dichloro-10-camphorsulfonyl)oxaziridine (DCCSO) to the desired (R)-sulfoxide (V). Conversion to the hydrochloride salt, followed by condensation with cyanamide (III) afforded the title chiral compound.