Table 3.
Electronic effects of aryl substution on peptide structure (Ktrans/cis of the prolyl amide bond).
| Ac-TXPN-NH2, X= | ktrans/cis | ΔGtrans/cis kcal mol−1 | ΔΔGtrans/cis kcal mol−1 |
|---|---|---|---|
| 4-S−-Phe (4, pH 8.5) | 2.2 | -0.47 | 0.22 |
| 4-S-SPyridyl-Phe (20) | 2.9 | -0.63 | 0.06 |
| 4-SAllyl-Phe (6) | 3.3 | -0.71 | -0.02 |
| 4-SH-Phe (4, pH 4.0) | 3.5 | -0.74 | -0.05 |
| 4-SCH3-Phe (17) | 3.5 | -0.74 | -0.05 |
| 4-SPh-Phe (5) | 3.6 | -0.76 | -0.07 |
| 4-S-SGlutathione-Phe (21) | 3.7 | -0.77 | -0.08 |
| 4-SAc-Phe (2) | 4.3 | -0.86 | -0.17 |
| 4-SO3−-Phe (24) | 4.4 | -0.88 | -0.19 |
| 4-S(2-Nitrobenzyl)-Phe (18) | 4.4 | -0.88 | -0.19 |
| 4-S(O)Me-Phe (22) | 4.7 | -0.92 | -0.23 |
| 4-SO2Me-Phe (23) | 5.9 | -1.05 | -0.36 |
| Phe (F)a | 3.2 | -0.69 | 0.00 |
| Tyr (Y)a | 2.7 | -0.59 | 0.10 |