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An NMR and conformational investigation of the trans‐syn cyclobutane photodimers of dTpdU
Author(s) -
Tabaczynski Walter A.,
Lemaire Danielle G. E.,
Ruzsicska Bŕla P.,
Alderfer James L.
Publication year - 1993
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.360330907
Subject(s) - chemistry , cyclobutane , conformational isomerism , heteronuclear molecule , deoxyribose , stereochemistry , homonuclear molecule , nuclear overhauser effect , nuclear magnetic resonance spectroscopy , diastereomer , chemical shift , two dimensional nuclear magnetic resonance spectroscopy , ring (chemistry) , crystallography , molecule , nucleic acid , organic chemistry , biochemistry
Two trans‐syn cyclobutane photodimers of thymidylyl (3′–5′) deoxyuridine were formed by deamination of the corresponding trans‐syn cyclobutane photodimers of thymidylyl(3′–5′) deoxycytidine and were examined by 1 H−, 13 C−, and 31 P‐nmr spectroscopy. Correlation spectroscopy, nuclear Overhauser enhancement spectroscopy, and one‐dimensional heterodecoupling experiments allowed a more complete assignment of the 1 H spectra, compared with previous reports by Koning et al. [ (1991) European Journal of Biochemistry , Vol. 195, pp. 29–40] and Liu and Yang [(1978) Biochemistry , Vol. 17, pp. 4865–4876]. Deoxyribose ring conformations were calculated from 1 H coupling constants by pseudorotational analysis, and rotamer distributions of exocyclic bonds were calculated from the observed homonuclear and heteronuclear coupling constants. The cyclobutane ring configuration (CB) of each isomer was identified, using arguments based upon observed scalar and dipolar couplings. Glycosidic bond conformation was ascertained from nuclear Overhauser enhancements observed between base and deoxyribose protons. Isomer I (S‐type class; CB − ; SYN‐ANTI) and isomer II (N‐type class; CB + ; ANTI‐SYN) exhibit markedly different conformational features. 31 P chemical shifts and exocyclic bond rotamer distributions indicate diminished backbone flexibility for both photoproducts relative to parent thymidylyl (3′–5′) deoxyuridine. Isomer I (SYN‐ANTI) is particularly rigid, while isomer II (ANTI‐S YN) maintains some flexibility. Also, 13 C spectra were acquired and assigned unequivocally with the aid of short‐ and long‐range two‐dimensional heteronuclear shift correlation experiments. © 1993 John Wiley & Sons, Inc.