Crystallographic structure of a multiple β-turn containing,glycine-rich heptapeptide: A synthetic precursor of the lipopeptaibol antibiotic Trichodecenin I

In continuation of our studies on the structure and function of peptaibol antibiotics, the conformational properties of a sequence analogous to that of Trichodecenin I (Z-Gly-Gly-D -Leu-Aib-Gly-D -Ile-D -Leu-OMe, where Z = benzyloxycarbonyl, Aib = α-aminoisobutyric acid, and OMe = methyl ester) have been investigated crystallographically. This sequence is the mirror image of the naturally occurring molecule and also of the C-terminal heptapeptide of the related lipo-peptaibol Trichogin A IV (where, however, the Leu-OMe residue has replaced the original Leuol residue). The molecule crystallized in the monoclinic system, space group P2₁, Z = 4, and cell parameters a = 11.610(5), b = 33.342(8), c = 11.735(4) Å, β = 110.42(1)*, V = 4257(3) ų. The crystallographic refinement converges at residual values of R = 0.047 and wR₂ = 0.134 on F². In the 1–5 segment the molecular conformation is virtually identical to that one reported from solution nmr studies of a similarly protected sequence [Biopolymers (1995), Vol. 35, pp. 21–29)] and is characterized by β-turns of type I at Gly1-Gly2, II′ at Leu3-Aib4, and I at Aib4-Gly5. In the crystal structure, a β-sheet-like arrangement is seen at the C-terminus. © 1996 John Wiley & Sons, Inc.