Resolution of L-653180, (_+)-9-{[(Z)-2-(hydroxymethyl)cyclohexyl]-methyl}guanine, a racemic, nonsubstrate inhibitor of HSV-TK, was achieved and the absolute stereochemistry of the enantiomers was determined. Enzyme inhibition was shown to reside in the enantiomer with [1S,2R] stereochemistry in the cyclohexyl sidechain. An enantioselective synthesis of the more active L-653180 stereoisomer was devised. @ 1997 Elsevier Science Ltd. All rights reserved.
During investigations on identifying novel inhibitors of herpes simplex virus thymidine kinase (HSV-TK), L-653180, prepared as the racemate la and lb, (Figure ), was found to be a potent, nonsubstrate inhibitor of HSV-TK. l Separation and independent testing of the enantiomers was undertaken to determine if they possessed differential activity towards HSV-TK.
The most expedient way to separate the enantiomers was to utilize chiral HPLC. It was found that baseline separation of the enantiomers could be achieved on a ChiralPak AD column (Figure ). Although L-653180 was sparingly soluble in the mobile phase (hexane:ethanol 95:5), several milligrams of each enantiomer were isolated for biological assay. The faster isomer, identified as la, (Tr=13.4 min) had a Ki=0.14 laM whereas the slower isomer, lb, (Tr=16.7 min) had a Ki=17 laM against the HSV-TK as calculated by the Dixon plot of I/V against inhibitor concentration at various thymidine concentrations.