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Structure in solution of biscyclo(dipeptide) restricted by CSSC gauche effect
Author(s) -
Ueyama Norikazu,
Araki Takeo
Publication year - 1981
Publication title -
biopolymers
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.556
H-Index - 125
eISSN - 1097-0282
pISSN - 0006-3525
DOI - 10.1002/bip.1981.360201202
Subject(s) - chemistry , trifluoroacetic acid , conformational isomerism , chloroform , raman spectroscopy , dipeptide , stereochemistry , cystine , methanol , crystallography , amino acid , molecule , cysteine , organic chemistry , biochemistry , physics , optics , enzyme
Biscyclo(Cys‐Sar) [I] and biscyclo(Cys‐Pro) [II] were prepared by the extension of amino acid moieties from cystine. Compound I equilibrates between two rotamers around the CSSC bond of the cystine residue in methanol, showing dual negative CD transitions (CS‐SC) at 270 and 255 nm, and dual S‐S vibrations at 507 and 539 cm −1 in Raman spectra. In contrast, a conformation of P‐helix type is suggested in CH 3 CN, which shows a distinct negative CD at 270 nm and only one Raman band at 507 cm −1 for the S‐S bond. Compound II rotates freely in dimethylsulfoxide (Me 2 SO) but takes a relatively stable conformer of P‐helix type in methanol, chloroform/Me 2 SO (9:1), and chloroform/trifluoroacetic acid (9:1). The conformation in chloroform is retained even on addition of trifluoroacetic acid. A more complete conformation of compound II in water was determined from the negative CD of S‐S transition and 1 H‐nmr spectra of the Cys‐β‐CH 2 protons.