Alkoxycarbonyl elimination of 3-O-substituted glucose and fructose by heat treatment under neutral pH
Alkoxycarbonyl elimination of 3-O-substituted glucose and fructose by heat treatment under neutral pH
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DOI：
10.1016/j.carres.2020.108129
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发表时间：
2020-10-01
影响因子：
3.1
通讯作者：
Kitaoka, Motomitsu
中科院分区：
文献类型：
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作者：
Chiku, Kazuhiro;Tsukasaki, Riku;Kitaoka, Motomitsu
3-O-取代的还原醛糖在中性和碱性 pH 值的热处理下通常不稳定。在本研究中，为了评估分解产物，将黑曲霉糖（3-O-α-D-吡喃葡萄糖基-D-葡萄糖）和 3-O-甲基葡萄糖在 100 mM 磷酸钠缓冲液（pH 7.5）中加热至 90 摄氏度。观察到通过β-消除的分解，形成3-脱氧-阿拉伯-己酸和3-脱氧-核糖-己酸的混合物；经过进一步的酸处理，它被转化为γ-内酯。同样，松二糖（3-O-α-D-吡喃葡萄糖基-D-果糖）是黑糖的酮糖异构体，在相同条件下比黑糖分解得更快，形成相同的产物。这些发现表明，3-O-取代的还原性葡萄糖和果糖通过相同的 1,2-烯二醇中间体分解。如果 O-糖苷键位于与 1,2-烯二醇中间体相邻的碳上，则 3-O-取代的还原性葡萄糖和果糖的烷氧基羰基消除很容易发生。根据这些实验，我们提出了在中性 pH 条件下通过热处理对黑曲霉糖和松二糖进行 3-分解的动力学模型。所提出的模型与本研究中收集的实验数据非常吻合。黑曲霉糖的分解速率常数为(1.2 +/- 0.1) x 10(-4) s(-1)，而松二糖的分解速率常数[(2.6 +/- 0.2) x 10(-4) s(-1)]大约高2.2倍。
3-O-Substituted reducing aldoses are commonly unstable under heat treatment at neutral and alkaline pH. In this study, to evaluate the decomposition products, nigerose (3-O-alpha-D-glucopyranosyl-D-glucose) and 3-O-methyl glucose were heated at 90 degrees C in 100 mM sodium phosphate buffer (pH 7.5). Decomposition via beta-elimination was observed that formed a mixture of 3-deoxy-arabino-hexonic acid and 3-deoxy-ribo-hexonic acid; upon further acid treatment, it was converted to their gamma-lactones. Similarly, turanose (3-O-alpha-D-glucopyranosyl-D-fructose), a ketose isomer of nigerose, decomposed more rapidly than nigerose under the same conditions, forming the same products. These findings indicate that 3-O-substituted reducing glucose and fructose decompose via the same 1,2-enediol intermediate. The alkoxycarbonyl elimination of 3-O-substituted reducing glucose and fructose occurs readily if an O-glycosidic bond is located on the carbon adjacent to the 1,2-enediol intermediate. Following these experiments, we proposed a kinetic model for the3-decomposition of nigerose and turanose by heat treatment under neutral pH conditions. The proposed model showed a good fit with the experimental data collected in this study. The rate constant of the decomposition for nigerose was (1.2 +/- 0.1) x 10(-4) s(-1), whereas that for turanose [(2.6 +/- 0.2) x 10(-4) s(-1)] was about 2.2 times higher.