Institut für Lebensmittelchemie, Technische Universität Braunschweig, Schleinitzstr. 20, 38106, Braunschweig, Germany.
Anal Bioanal Chem. 2009 Nov;395(6):1749-68. doi: 10.1007/s00216-009-3013-4. Epub 2009 Aug 19.
Dextrans from Leuconostoc ssp., alpha-1,6-linked glucans branched at O-3, were O-methylated in DMSO with lithium dimsyl and methyl iodide under various conditions. Methyl substituent distribution was comprehensively studied in the terminal, internal, and branched glucosyl units and along and over the dextran macromolecules. The order of reactivity was O-2 > O-4 > or = O-3. The methyl pattern in the glucosyl units significantly deviates from a random distribution with enhanced amounts of un- and trisubstituted moieties. This deviation was found to proceed on macromolecular level by means of ESI-MS of perdeuteromethylated and partially depolymerized methyl dextrans. Heterogeneity was much more pronounced than for methyl amylose prepared under comparable conditions. DS gradients in and over the material are discussed with respect to dextran structure and the mechanism of Li dimsyl alkylation. For comparison, cyanoethyl dextrans were prepared by sodium hydroxide catalyzed addition of acrylonitrile. Monomer analysis of cyanoethyl dextrans revealed that this thermodynamically controlled reaction gave a random substitution pattern with 48% of cyanoethyl groups at O-2, 33% at O-4, and 19% at O-3.
从乳球菌属的支链α-1,6-连接葡聚糖，在二甲基亚砜中，用双（三甲基甲硅烷基）亚胺锂和碘甲烷在不同条件下进行 O-甲基化。在末端、内部和支化的葡糖基单元以及沿和超过葡聚糖大分子上，全面研究了甲基取代基的分布。反应性顺序为 O-2 > O-4 > 或 = O-3。葡糖基单元中的甲基模式与随机分布显著偏离，未取代和三取代部分的数量增加。通过对全氘代甲基化和部分解聚的甲基葡聚糖的 ESI-MS 研究，发现这种偏差是在大分子水平上进行的。对材料内部和上方的 DS 梯度进行了讨论，以了解葡聚糖结构和 Li 二甲硅烷基化的机制。作为比较，通过氢氧化钠催化丙烯腈的加成制备了氰乙基葡聚糖。氰乙基葡聚糖的单体分析表明，这种热力学控制的反应具有随机取代模式，O-2 位的氰乙基基团占 48%，O-4 位占 33%，O-3 位占 19%。
