Synthesis and biological properties of a new series of 1β-methyl carbapenems that have been variously substituted thiazol-2'-ylthio side chain on C-2 are described. Amongst synthesized compounds, 4'arylthiazole derivatives showed potent anti-MRSA activity and the introduction of a quaternary cation was effective to reduce binding to human serum albumin without affecting the anti-MRSA activity.