Table 1. Efficiency and Yield of Labeling Reaction with SAL-Esters 1a–f^a.

entry	SAL-ester	yield
1	1a	12 h, 31%
2	1b	12 h, trace amountb
3	1c	12 h, trace amountc
4	1d	3 h, 36%
5	1e	3 h, 63%
6	1f	3 h, 50%

^aConditions: phosphate buffer (0.1 M, pH 7.0), DMSO (2%, v/v), room temperature. The concentration of SAL-ester was 10 mM, and the concentration of Ac-3AT-OMe was 10 mM.

^bThe majority of 1b was consumed by hydrolysis in the buffer.

^cNo desired product was isolated due to the low reaction conversion.