Planas A, Abel M, Millet O, Palasí J, Pallarés C, Viladot J L
Department of Organic Chemistry, Institut Químic de Sarrià, Universitat Ramon Llull, Barcelona, Spain.
Carbohydr Res. 1998 Aug;310(1-2):53-64. doi: 10.1016/s0008-6215(98)00175-x.
A series of substituted aryl beta-glycosides derived from 3-O-beta-cellobiosyl-D-glucopyranose with different phenol-leaving group abilities as measured by the pKa of the free phenol group upon enzymatic hydrolysis has been synthesised. Aryl beta-glycosides with a pKa of the free phenol leaving group > 5 were prepared by phase-transfer glycosidation of the per-O-acetylated alpha-glycosyl bromide with the corresponding phenol, whereas the 2,4-dinitrophenyl beta-glycoside was obtained by condensation of 1-fluoro-2,4-dinitrobenzene with the partially acetylated trisaccharide followed by acid de-O-acetylation. The aryl beta-glycosides have been used for reactivity studies of the wild-type Bacillus licheniformis 1,3-1,4-beta-D-glucan 4-glucanohydrolase. The Hammett plot log kcat versus pKa is biphasic with an upward curvature at low pKa values suggesting a change in transition-state structure depending on the aglycon.
合成了一系列由3 - O - β - 纤维二糖基 - D - 吡喃葡萄糖衍生而来的取代芳基β - 糖苷，这些糖苷具有不同的酚离去基团能力，通过酶促水解时游离酚基团的pKa来衡量。通过将全O - 乙酰化的α - 糖基溴与相应的酚进行相转移糖苷化反应，制备了游离酚离去基团pKa > 5的芳基β - 糖苷，而2,4 - 二硝基苯基β - 糖苷则是通过1 - 氟 - 2,4 - 二硝基苯与部分乙酰化的三糖缩合，然后进行酸脱O - 乙酰化反应得到的。这些芳基β - 糖苷已用于野生型地衣芽孢杆菌1,3 - 1,4 - β - D - 葡聚糖4 - 葡聚糖水解酶的反应性研究。哈米特图（log kcat对pKa）呈双相，在低pKa值时向上弯曲，表明过渡态结构根据糖苷配基而发生变化。
