Table 2. Probing the Aromatic System on the Dipeptide N-Terminus.

| compd. | R | % inhibitiona |
|---|---|---|
| 17 | biphenyl | 77 |
| 18 | 4-cyclohexylphenyl | 57 |
| 19 | phenyl | 52 |
| 20 | 3,5-dichlorophenyl | 100 |
| 21 | meta-tert-butylphenyl | 93 |
| 22 | para-bromophenyl | 87 |
| 23 | para-chlorophenyl | 77 |
| 24 | meta-chlorophenyl | 79 |
| 25 | 3,4-diethoxyphenyl | 22 |
| 26 | 2,6-dichlorophenyl | 83 |
Dipeptides were evaluated at 15 μM with 20 nM BoNT/A LC and 8 μM SNAPtide substrate. Enzyme reactions were performed in triplicate, and the percent inhibition reported is the average.