Table 1. Reaction Conditions for the Preparation of 1ca.
| entry | coupling agent (equiv) | incubation time (min)b | yield of 1c (%) |
|---|---|---|---|
| 1 | HBTU (1.1) | 15 | 15 |
| 2b | HBTU (1.2) | 15 | 61 |
| 3 | HATU (1.0) | 15 | 68 |
| 3 | HATU (1.0) | 60 | 72 |
| 4a | HATU (1.2) | 60 | 91 |
| 5 | HATU (1.5) | 60 | 60 |
a
Reaction conditions: To the solution of phenylalanine (0.26 M), N-methylmorphorine (NMM) (2 equiv) was added with Dbz (1.3 equiv) in four portions every 10 min under N2. The reaction was carried out at room temperature for 140 min under N2.
b
The mixing time of 2 and coupling agents.