✦ LIBER ✦

Synthesis, crystal structure, and molecular conformation of N-Boc-L-Phe-dehydro-Leu-L-Val-OCH3

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

Publisher: Wiley (John Wiley & Sons)
Year: 1990
Tongue: English
Weight: 509 KB
Volume: 29
Category: Article
ISSN: 0006-3525
DOI: 10.1002/bip.360290606

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✦ Synopsis

The peptide N-Boc-L-Phe-dehydro-Leu-L-Val-OCH3 was synthesized by the usual workup procedure and finally by coupling the N-Boc-L-Phe-dehydro-Leu-OH to valine methyl ester. It was crystallized from its solution in methanol-water mi5ture a t 4°C. The crystals belong to the triclinic space group P1 with a = 5.972(5) A, b = 9.455(6) A, c = 13.101(6) A, a = 103.00(4)", = 97.14(5)", y = 102.86(5)', V = 690.8(8) A, Z = 1, dm = 1.179(5) Mg m -3 and dc = 1.177(5) Mg m-3. The structure was determined by direct methods using SHELXS86. It was refined by block-diagonal least-squares procedure to an R value of 0.060 for 1674 observed reflections. The CZ-C! distance of 1.323(9) A in dehydro-leu is an appropriate double bond length. The bond angle C"-Cp-Cv in the dehydro-leu residue is 129.4(8)". The peptide backbone torsion angles are 8' = -168.6( )", 31.1(10)", w2 = 171.7( )", +3 = 51.9(8)", 4; = 139.0(6)', BT = -175.7(6)". These values show that the backbone adopts a p-turn I1 conformation. As a result of p-turn, an intramolecular hydrogen bond is formed between the oxygen of the i t h residue and NH of the ( i + 3)th residue at a distance of 3.134(6) A. The Boc group has a trans-trans conformation. The side-chain torsion angles of the Phe residue are x1 = 171.6(6)", xf' = -l02.1(9)", and xt2 = 78.6(10)". The side-chain conformational angles of dehydro-leu 12.

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