ß‐helices of D,L‐alternating valine peptides

Abstract

New conformational data for members of the series BOC-(D-V~~),-(L-V~~~-V~~)(,.,),~-OM~ (rn = 0 or 1 ; n = total number of residues) are presented and used together with earlier results to formulate general conclusions regarding types and relative stabilities of 8-helices formed by D,L-alternating valine peptides. The helices, singleor double-stranded, are of the tightest geometry, the single-stranded helices having only 4,4 residues per turn (84s4-helices) and the double-stranded ones only about 5,6 residues per turn (tl p5p6-and ?t fi5s6-helices). The doublestranded helices are of the type with the highest possible number of interstrand H-bonds [2(n-l)] and the antiparallel ones are always strongly preferred. In chloroform solution right-and lefthanded @4-helices and left-handed tl /35*6-and ?? /35*6-helices are formed by the oligovalines studied with different preferences depending on the peptide chain length and on the parity of the number (odd or even) of residues. The reasons for these preferences are discussed.

Conformational characteristics of alternating stereo‐co‐oligopeptides of D‐ and L‐norleucine: influence of an N‐methyl group

“…Final steps in the preparation of the N-methylated oligonorleucines. TFA is trifluoroacetic acid 9.78;N,11.08;Found: C,62.80;H,10.05;N,10. ,9.78;N,11.18;Found: C,62.80;H,9.73;N,11.06. {Me,2H}Boc-15-OMe: Rf, 0.76; m.p. 275-7 "C;…”

“…General. The synthesis of the oligonorleucines was carried out by the same conventional methods already used in our laboratory for the synthesis of other peptides (8,10,20). For the formation of the peptide bond the mixed-anhydride method (2 1) with isobutyl chloroformate as the mixed anhydride forming reagent was used.…”

Conformationally constrained D,L‐alternating oligopeptides

“…In this case, these and the t.l /37.2-helices of one of the two possible kinds are the helices that represent the structures with the maximum number of interchain H bonds [only two free NHs at positions (n) and (n -2)]. (11) are easily soluble in chloroform and other solvents of low polarity. This solubility behavior of I and I1 markedly contrasts with the insolubility in all common solvents that characterizes7 nonmethylated D,L-alternating oligonorleucines of the same type, and of the same or comparable length, and shows the ability of even a single NMe group of preventing an aggregation of the peptide chains.…”

“…In particular, as shown in Table I, P4e4-, t t b5*6-, and t f fi7*2-helices, all of which require a NH in the (n -3), ( n -4), or both positions for the H bonding, are not expected. If n is odd and the NMe group is in the (n -3) position there is only one kind of f 1 B7"-helix possible (Table I) (11) are easily soluble in chloroform and other solvents of low polarity. This solubility behavior of I and I1 markedly contrasts with the insolubility in all common solvents that characterizes7 nonmethylated D,L-alternating oligonorleucines of the same type, and of the same or comparable length, and shows the ability of even a single NMe group of preventing an aggregation of the peptide chains.…”

Vibrational spectroscopic studies of L,D‐alternating phenylalanine peptides

“…Peptides and polypeptides containing a regularly alternating sequence of L-and D-amino acid residues have received a great deal of attention in recent years. This is mainly due to their analogy with gramicidin A, a naturally occuring linear pentadecapeptide that dimerizes to form cation-selective channels in biological and artificial membranes (1)(2)(3)(4)(5)(6)(7)(8)(9)(10)(11)(12)(13)(14)(15). Peptides of bacterial cell walls contain D-amino acids in a sequence of alternating L,D residues (16).…”