Nucleosidsynthesen, VIII. NMR‐ und CD‐Spektren von Pyrimidin‐nucleosiden und ihren 2‐Thioanaloga

Abstract

Es wird eine Reihe von Pyrimidin‐nucleosiden und ihren 2‐Thioanaloga NMR‐ und CD‐spektrometrisch untersucht. Beim Übergang von den Sauerstoff‐ zu den Schwefelverbindungen wird in der β‐Reihe das 1′‐H stark, die beiden 5′‐H schwach und, sofern vorhanden, das 2α′‐H mittelstark paramagnetisch verschoben. Bei den 2′‐Desoxyuridinen mit α‐Verknüpfung werden das 1′‐H, 2α′‐H, 2β′‐H, 3′‐H und 4′‐H mit in der angegebenen Reihenfolge abnehmender Stärke zu tieferem Feld verschoben, während die beiden 5′‐H sich nicht mehr verändern. Die Aufspaltungen J′1′2′ werden durchweg verkleinert. Nach diesen Befunden herrschen sowohl in der α‐ als auch in der β‐Reihe die anti‐Formen vor. In den CD‐Spektren besitzen anomere Nucleosidpaare Kurven von entgegengesetztem Vorzeichen. Die Einführung der 6‐Azagruppe führt zur Umkehrung des Vorzeichens der kürzerwelligen Banden. Beides gilt sowohl für die Sauerstoff‐ als auch für die Schwefelverbindungen.

Naphthalene, Phenanthrene, and Pyrene as DNA Base Analogues: Synthesis, Structure, and Fluorescence in DNA

“…12,27 Comparison of the H1′-H2′ coupling constants shows considerable differences, however. The β-thymidine values (7.0 and 7.0 Hz) 24 are similar to those for the α-anomer of the difluorotoluene nucleoside (7.6 and 7.6 Hz), and both resonances appear as pseudotriplets. Conversely, the α-anomer of thymidine has coupling constants (8.0 and 3.0 Hz) which are similar to those for the β-anomer of the difluorotoluene nucleoside (10.4 and 4.6 Hz), and these appear as doublets of doublets.…”

“…12 By comparison, the α-anomers of the natural DNA N-nucleosides have considerably different coupling constants for this same H1′ resonance; for α-thymidine these are found to be 8.0 and 3.0 Hz, and the resonance appears as a doublet of doublets. 24 Virtually the same coupling constants are found for β-and α-deoxyadenosine as well. 25 This difference between the two isomers arises from the different dihedral angles which are present in the two anomeric isomers.…”

“…21,24 The two coupling constants are of the same magnitude; for example, those of β-thymidine are 7.0 and 7.0 Hz, 24 and thus the H-1′ resonance usually appears as a pseudotriplet. This has also held true for other Nnucleosides containing base moieties not found in DNA.…”

C-Nucleosides Derived from Simple Aromatic Hydrocarbons

“…We studied the H1'-H2' coupling constants for the two anomers of the isostere 18 and compared them to literature values for α-and β-thymidine. 33 In the literature it is observed that β-anomers of the natural deoxynucleosides give splitting patterns for H-1' which resemble a triplet, meaning the two coupling constants are similar. Interestingly, we observe that it is the opposite (α)-anomer of the isostere which appears as a triplet.…”

Enzymatic synthesis and phosphorolysis of 4(2)-thioxo- and 6(5)-azapyrimidine nucleosides by E. coli nucleoside phosphorylases

“…Analysis of the NMR spectra of 6Me Ud in D 2 O pointed to the predominant base population in the syn -conformation [62]. The stereochemistry of 6-methyluridine was also investigated by physicochemical methods [63–65] and in crystal [66] and the dominating syn base conformation around the glycosyl bond was established.…”