The precursor 5 (0.33 mmol) was taken up in H2O (10 ml) and stirred rapidly in a 10 ml round bottom flask fitted with an addition funnel. The pH was adjusted to 8.5 with solid NaHCO3 and thiophosgene (42 mg, 0.365 mmol) in CHCl3 (10 ml) was added dropwise. Stirring was continued until the solution tested negative for amine by the fluorescamine method. The aqueous layer was taken to dryness. Purification was done by column chromatography on a 1×30 cm Florisil™ column eluted with acetonitrile:water (30:8). The product eluted from the column cleanly as determined by TLC and was stored in a dessicator in a freezer and re-purified immediately prior to use.
