Snyder J R, Serianni A S
Department of Chemistry, University of Notre Dame, IN 46556.
Carbohydr Res. 1988 Dec 31;184:13-25. doi: 10.1016/0008-6215(88)80002-8.
The anomerization of 5-deoxy-L-pentoses (1-4) and 5-O-methyl-D-pentoses (5-8) in aqueous solution has been studied by 13C saturation-transfer n.m.r. (s.t.-n.m.r.) spectroscopy, using compounds substituted with 13C at the anomeric carbon atom. Unidirectional rate-constants of ring-opening (k open) and ring-closing (k close) have been obtained for these compounds under identical solution conditions (50mM acetate buffer, pH 4.0 at 60 degrees), and have been compared to those measured for the D-tetroses (9 and 10) and the four D-pentose 5-phosphates (11-14). Based on these comparisons, several correlations between furanose structure and reactivity have been revealed, and models have been proposed to explain the observed kinetic behavior of compounds (1-10). The effect of exocyclic structure on acid-catalyzed rate-constants was also examined by comparing the behavior of 5-deoxy-L-(1-13C)-lyxose and 5-O-methyl-D-(1-13C)lyxose. Some consideration has been given to identifying the factors (enthalpic and entropic) that may play roles in determining the effect of structure on anomerization reactivity.
利用在异头碳原子处被(^{13}C)取代的化合物，通过(^{13}C)饱和转移核磁共振（s.t.-n.m.r.）光谱研究了5-脱氧-L-戊糖（1-4）和5-O-甲基-D-戊糖（5-8）在水溶液中的异头化作用。在相同的溶液条件下（50mM醋酸盐缓冲液，60℃时pH为4.0），获得了这些化合物的单向开环速率常数（(k_{open})）和闭环速率常数（(k_{close})），并将其与对D-丁糖（9和10）以及四种D-戊糖5-磷酸酯（11-14）测得的速率常数进行了比较。基于这些比较，揭示了呋喃糖结构与反应活性之间的几种相关性，并提出了模型来解释所观察到的化合物（1-10）的动力学行为。通过比较5-脱氧-L-（1- (^{13}C)）-来苏糖和5-O-甲基-D-（1- (^{13}C)）-来苏糖的行为，还研究了环外结构对酸催化速率常数的影响。已经考虑了确定可能在决定结构对异头化反应活性影响中起作用的因素（焓和熵）。
