Table 2.
Overall functional group effects on cis-trans isomerism in Ac-TYXN-NH2 peptides. ΔΔG = ΔGtrans/cis(4R stereoisomer) − ΔGtrans/cis(4S stereoisomer), with negative ΔG consistent with the magnitude of stereoelectronic effects and positive ΔG indicating steric effects dominating over stereoelectronic effects. By definition, for Pro (4R = 4S = H), ΔΔG = 0.00.
| Ac-TYP(4-X)N-NH2 X = | ΔΔG(4R-4S) kcal mol-1 |
|---|---|
| ONH3+ | -1.13 |
| isobutylaminoacetoxy | -0.93 |
| β-Alanyl ester | -0.92 |
| F | -0.91 |
| OBzNO2 | -0.90 |
| OC(O)CH2Br | -0.88 |
| OBzCF3 | -0.87 |
| hydroxyphthalimide | -0.81 |
| OAc | -0.76 |
| O-pivaloyl | -0.76 |
| OC(O)CH2N3 | -0.74 |
| O-(2,6-(CH3)2Ph) | -0.71 |
| OC(CF3)3 | -0.71 |
| succinyl ester | -0.68 |
| allylthioetheracetoxy | -0.64 |
| OPO3H- | -0.60 |
| OMs | -0.60 |
| OC6F5 | -0.56 |
| OPh | -0.50 |
| maleinyl ester | -0.49 |
| β-Ala-guanidinyl ester | -0.45 |
| OPO3Et2 | -0.44 |
| OH | -0.43 |
| azido | -0.41 |
| OPhCN | -0.41 |
| OMst | -0.39 |
| ONs | -0.33 |
| guanidinyl | -0.31 |
| 5′-Ph-(1H-1,2,3-triazol-1-yl) | -0.28 |
| OTs | -0.17 |
| S(O)Ph | -0.06 |
| 4′-Ph-(1H-1,2,3-triazol-1-yl) | -0.04 |
| SPh | 0.04 |
| SPhNO2 | 0.06 |
| SAc | 0.06 |
| 4′-hexyl-(1H-1,2,3-triazol-1-yl) | 0.15 |
| SH | 0.17 |
| SePh | 0.18 |
| SO2Ph | 0.22 |
| phthalimide | 0.33 |
| +NH3 | 0.33 |