In order to develop general rules of peptide design with α,β-dehydro-residues, a peptide, Boc-Ala-ΔPhe-ΔPhe-Phe-OCH3, was synthesized. The peptide was crystallized from its solution in an acetone:water mixture (70:30). The crystals belong to orthorhombic space group P212121 with a = 9.403(1) Å, b = 16.871(1) Å, c = 21.638(1) Å, and Z = 4. The peptide adopts a conformation with two overlapping types II′ and III β-turns having dihedral angles, φ1 = 53.7(6)∘, ψ1 = −135.9(4)∘, φ2 = −59.2(5)∘, ψ2 = −17.9(5)∘, φ3 = −68.4(5)∘, ψ3 = −18.8(6)∘. The conformation was further characterized by two intramolecular 4 → 1 hydrogen bonds involving imino nitrogen atoms of ΔPhe3 and Phe4 as donors and carbonyl oxygen atoms of blocking group Boc and Ala1 as acceptors. The packing of the molecules in the unit cell is stabilized by an intermolecular hydrogen bond, N2–H2⋅s O′3 [−x, y+1/2, −z+1/2] = 2.894 Å and van der Waals forces involving aromatic side chains.
为了制定α、β-脱氢残基
多肽设计的一般规则,我们合成了一种名为 Boc-Ala-ΔPhe-ΔPhe-Phe-OCH3 的
多肽。该肽在
丙酮和
水(70:30)的混合溶液中结晶。晶体属于正交空间群 P212121,a = 9.403(1) Å,b = 16.871(1) Å,c = 21.638(1) Å,Z = 4。该肽具有两个重叠的 II′ 型和 III β-匝构象,其二面角为 φ1 = 53。7(6)∘, ψ1 = -135.9(4)∘, φ2 = -59.2(5)∘, ψ2 = -17.9(5)∘, φ3 = -68.4(5)∘, ψ3 = -18.8(6)∘.该构象的进一步特征是分子内有两个 4 → 1 的氢键,其中 ΔPhe3 和 Phe4 的亚
氨基氮原子为供体,阻遏基团 Boc 和 Ala1 的羰基氧原子为受体。分子间氢键 N2-H2⋅s O′3 [-x, y+1/2, -z+1/2] = 2.894 Å 和涉及芳香族侧链的范德华力稳定了单胞中分子的堆积。