Structural studies of leucinostatin A and its Boc‐Aib‐Leu‐Leu‐Aib‐OMe tetrapeptide fragment

Abstract

The conformational behaviour of the peptide antibiotic leucinostatin A has been studied in solvents of different polarity using circular dichroism (CD) and infrared (i.r.) absorption. I.r. studies provided evidence of an intramolecularly hydrogen‐bonded structure in CDC3 while CD studies suggested a helical conformation in leucinostatin A in lipophilic solvents. The tetrapeptide Boc‐Aib‐Leu‐Leu‐Aib‐OMe, a fragment of leucinostatin A, was also studied both in solution and in solid state using X‐ray diffraction. The crystal structure shows that the peptide backbone folds into a right‐handed 310‐helical conformation stabilized by two intramolecular 4 → 1 hydrogen bonds. The spectroscopic analysis in solution is consistent with the conformation found in solid state. Crystal data: orthorhombic, P212121, a= 23.583, b= 15.791, c= 9.554 Å Z = 4; the final R and Rw are 0.090 and 0.126, respectively.

New Type of Helix and 27Ribbon Structure Formation in Poly ΔLeu Peptides: Construction of a Single-Handed Template

“…The geometry of Ac-∆Leu-NHMe in both the Z and E forms was optimized by using a potential function of the type suggested by Vinter et al 51 and the optimized bond lengths and bond angles were in agreement with crystallographic data on dehydroamino acid residues. 52 Standard bond lengths and bond angles have been used for the Leu residues. 53,54 The Φ, Ψ maps and χ potential energy curves for ∆Leu were constructed in model dipeptide Ac-∆Leu-NHMe in both the Z and E forms, by systematic variation of two torsion angles in steps of 30°to have the knowledge of global, local and low-energy minima.…”

Conformational study of poly‐ΔAbu peptides and construction of amphipathic nanostructure

“…It is interesting to note that for the peptide Ac‐Ile‐ΔAbu‐NHMe with Ile residue in (i) L form and ΔAbu in both Z‐ and E‐ forms, same state with ϕ 1 = −30°, ψ 1 = 120° and ϕ 2 = ψ 2 = 30° is populated, (ii) D ‐ form and Δ E Abu, the peptide adopts the state with ϕ 1 = 30°, ψ 1 =−115° and ϕ 2 = ψ 2 = −30° as shown in Figure 3b. It may be mentioned that the structure with ϕ, ψ values of −30°, 120° is energetically favored over the helices for short peptide sequences and is well documented on the basis of computational results,46 database analysis,44, 45 CD,47, 48 and IR49 spectroscopic results. α,β‐dehydroamino acids in short peptides with preceding L or D chiral amino acid residue adopt ϕ, ψ values of ∼±30°, ±30° and facilitate the formation of hydrogen bond with the preceding L or D amino acids with ϕ, ψ values of ±30°, ∓120°, respectively, but does not introduce β‐turn.…”