Synthesis, crystal structure, and molecular conformation of peptide N-Boc-L-Pro-dehydro-Phe-L-Gly-OH

✍ Scribed by H. C. Patel; T. P. Singh; V. S. Chauhan; P. Kaur

• Publisher: Wiley (John Wiley & Sons)
• Year: 1990
• Tongue: English
• Weight: 461 KB
• Volume: 29
• Category: Article
• ISSN: 0006-3525
• DOI: 10.1002/bip.360290306

✦ Synopsis

The peptide N-Boc-L-Pro-dehydro-Phe-L-Gly-OH was synthesized by the usual workup procedure and finally coupling the N-Boc-L-Pro-dehydro-Phe to glycine. The geptide crystallizes monoclinic space group P2: with a = 8.951( ) A, b = 5.677(6) A, c = 21.192(11) A, p = 96.97(4)', V = 1069(1) A3, Z = 2, d, = 1.295(5) Mgn-', and d, = 1.297(4) M g ~r -~. The structure was determined by direct methods using SHELXS86. The structure was refined by the block-diagonal least-squares proceGure to an R value of 0.074 for 1002 observed reflections. The C;-C[ distance of 1.33(2) A is an appropriate double bond length. The angle C;-C!-C,Y is 133(1)'. The peptide backbone torsion angles are = 15(2)", w2 = -179(1)', and G3 = -166(1)". These values show that the Boc group has a trans-trans conformation while the peptide backbone adopts a p-turn I1 conformation, which is stabilized by an intramolecular hydrogen bond of length of 3.05(1) A. The structures of dehydro-Phe containing peptides suggest that the dehydro-Phe promotes the j3-turn I1 conformation. The five-membered pyrrolidine ring of the Pro residue adopts an ideal CY-ex0 conformation with torsion angles xi = -24(1)', x: = 34(1)O, x;? = -30(1)", x: = 15(1)', and 0; = 6(1)'. The side-chain torsion angles in dehydro-Phe are xi = -1(2)', x$' = ~ 176(1)", and xt2 = 8(2)'. The plane of C;-C[-C,Y is rotated with respect to the plane of the phenyl ring at 7(1)', which indicates that the atoms of the side chain of dehydro-Phe are essentially coplanar. The molecules form a 2, screw axis related hydrogen-bonded rows along the b axis.

8' = -167(1)', = 179(1)', GI = -48(1)', = 137(1)', w1 = 175(1)", 42 = 65(2)", $2 ' 1990 .John Wiley & Sons, Inc.