Nucleoside, XIII. Synthese und Eigenschaften von Lumazin‐ und Isopterin‐glucosiden

Abstract

Die Glncosidierung von Lumazin (l), Isopterin (2) sowie seinem 6,7-Dimethyl-Derivat (3) nach der ,,SilyI-Methode" wird beschrieben. Als Hauptreaktionsprodukte entstehen die 1X-l-Substitationsprodukte, die in Form ihrer Tetra-0-acetyl-Derivate (8, 10, 14) und der freien Glucoside 9 und 11 isoliert werden. Die Charakterisierung erfolgt durch UV-und NMR-spcktroskopische Untersuchungen, wobci aus letzteren crstmals cin expcrirnenteller Bcwcis iibcr das Vorliegeii von rotationsgehinderten syn-anti-Isomcren erbracht werden kann. Die freien Aktivicrungsenergien dcr Isomcrisierung haben Wertc um 18 kcaljmol. Nucleosides, XIU1) Synthesis and Properties of Lumazine and Isopterin GlucosidesThe glucosidation of lumazine (l), isopterin (2) and its 6,7-dimcthyl dcrivativc (3) via the ,,silyl method" is described. The reaction favours N-1 substitution and the tetra-0-acetyl derivatives & I 0 and 14 as well as the free glucosides 9 and 11 have been isolatcd and characterized by u.v.-and n.m.r. spectrophotometric studies. The latter provided for the first time an experimental proof for the existence of rotationally restricted syti-anti-isomcrs at room temperature. The free energies of activation of the isomerization have values around 18 kcat/ mol.In Erweiterung unserer Untersuchungen zur Direktglycosidierung von Pteridinen nahmen wir nach der erfolgreichen Darstellung der Lumazin-2) und Isopterinribosideu die Synthese der entsprechenden Glucoside in Angriff. Hierzu wurden Lumazin (l), Isopterin (2) und sein 6,7-Dimethyl-Derivat (3) zunachst in bekannter Weise durch Kochen in Hexaniethyldisilazan zu 4 bzw. 5 und 6 ,,silyliert" und anschlieRend wiederum in einer modifizierten Hilberf-Johnson-Birlcofer-Reaktion4) *) Diplomarbeit G. Ritzmnnn, Univ. Konstanz 1969.

1-Methylimidazolin-2-yl functionalized cyclopentadienyl complexes of titanium and zirconium. Crystal structure of {[η5:η1-κN-C5H4CPh2CH2-(1-Me–C3H4N2)]ZrCl2}2(μ-Cl)2

“…Meanwhile, the known greater basicity of imidazolines (pK 25 a (2-Me-C 3 H 6 N + 2 ) 11.1 [32]) comparatively to imidazoles (pK 25 a (2-Me-C 3 H 4 N + 2 ) 8.02 [33]), on one hand, and the greater reactivity of the imidazoline moiety (possibility to accept nucleophilic attacks at the 2nd position and ring-opening reactions), on the other, make them even somewhat more attractive than imidazoles for the purposes of coordination and organometallic chemistry of the Group 4 elements.…”

Synthesis, transformations and biological activity of chloro enamines and ynamines derived from chloroalkenyl- and alkynyl-N-substituted purine and pyrimidine bases of nucleic acids

“…It should be noted that the two rotameric (anti and syn) forms of N3-(P-~-glucopyranosyl)-6methyluracil were discernible by H NMR spectroscopy in the same ratio.25 Similar rotamers were also noted in some P-D-ghcopyranosylpteridines. 26 In these cases, the rotation of the sugar residue is hindered by two carbonyl groups or a carbonyl function and a heteroaromatic moiety. The obtained A G * -~a l u e s , ~~> ~~ 18.9 and 18.3 kcal mol-' (the former was calculated from the reported 2 5 data), indicate a similar rotational barrier in all these compounds.…”