Herein we describe the synthesis and conformational analysis of a series of bicyclic thymidine derivatives and their evaluation as inhibitors of thymidine monophosphate kinase from Mycobacterium tuberculosis (TMPKmt), based on previously discovered bicyclic sugar nucleosides. With a K(i) value of 2.3 microm, 1-[3-aminomethyl-3,5-dideoxy-2-O,6-N-(thiocarbonyl)-beta-D-ribofuranosyl]thymine emerged as the most potent TMPK inhibitor of this series. Moreover, this promising compound displays inhibitory potency against Mycobacteria cultures with an IC(99) value of 100 microg mL(-1), thus promoting TMPKmt for the first time as a validated target for further inhibitory design. Attempts to rationalise the observed structure-activity relationship (SAR) involving molecular modelling and conformational analysis are described.