Figure 1.

Stick representation of (A) Val and (B) Thr dipeptide mimetics. Both Val and Thr are shown in an α-helix backbone conformation (ϕ = −57°, ψ = −47°). The side-chain dihedral angle χ₁ (N-C_α-C_β-C_γ1) for both Val (χ₁ = 179.5°) and Thr (χ₁ = 117.7°), hydrogen dihedral angles θ₁ = 180° (C_α-C_β-C_γ1-${\text{H}}_{C_{\gamma 1}}^1$ on C_γ1) and θ₂ = 0° (C_α-C_β-C_γ2-${\text{H}}_{C_{\gamma 2}}^1$ on C_γ2) for Val and θ₁ = 180° (C_α-C_β-O_γ1-${\text{H}}_{C_{\gamma 1}}^1$) and θ₂ = 30° (C_α-C_β-C_γ2-${\text{H}}_{C_{\gamma 2}}^1$) for Thr are indicated.