CONFORMATIONAL-ANALYSIS OF THE ALPHA-L-ARABINOFURANOSIDES PRESENT IN WHEAT ARABINOXYLANS FROM PROTON PROTON COUPLING-CONSTANTS
CONFORMATIONAL-ANALYSIS OF THE ALPHA-L-ARABINOFURANOSIDES PRESENT IN WHEAT ARABINOXYLANS FROM PROTON PROTON COUPLING-CONSTANTS
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DOI：
10.1021/ja00036a020
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发表时间：
1992-05-06
影响因子：
15
通讯作者：
VLIEGENTHART, JFG
中科院分区：
文献类型：
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作者：
HOFFMANN, RA;VANWIJK, J;VLIEGENTHART, JFG
研究了小麦胚乳l -阿拉伯糖- d -木聚糖中存在的α - l -阿拉伯糖醛酸苷的构象行为。为此，对小麦胚乳l -阿拉伯糖- d -木聚糖酶切得到的低聚糖进行了z-过滤的一维同核哈特曼-哈恩（HOHAHA）光谱分析，并根据得到的邻近质子-质子耦合常数，利用适当的Karplus方程结合假旋动的概念推导了环构象。结果表明，α -l -阿拉伯糖苷与内部o- 3-单或o- 2,3-二取代(1-4)-连接的β -d -木吡喃糖残基的O3相连，存在等量的4E-4/0T （n型）和1/2T-2E （s型）构象平衡。而与内部o -2,3-二取代(1-4)-连接的β -d -木吡喃糖残基的O2连接的α -l -阿拉伯糖醛酸苷则以等量的4/3T-4E （n型）和1E-1/2T （s型）构象平衡存在。所研究的α - l -阿拉伯糖醛酸苷的N型和s型构象都含有刚性的C4-O4-C1-O1节段，假设O1为假轴取向，CH2OH为假赤道取向。从质子-质子耦合常数也可以确定外环旋转体的居群，显示出g-和t旋转体几乎相同的偏好。
The conformational behavior of alpha-L-arabinofuranosides present in wheat endosperm L-arabino-D-xylans has been investigated. To that purpose, oligosaccharides obtained by enzymatic digestion of a wheat endosperm L-arabino-D-xylan were submitted to z-filtered 1D homonuclear Hartmann-Hahn (HOHAHA) spectroscopy, and from the obtained vicinal proton-proton coupling constants, the ring conformation was deduced with the use of appropriate Karplus equations in conjunction with the concept of pseudorotation. The results revealed that alpha-L-arabinofuranosides linked to O3 of an internal O-3-mono- or O-2,3-disubstituted (1-4)-linked beta-D-xylopyranose residue are present in a conformational equilibrium of equal amounts of 4E-4/0T (N-type) and 1/2T-2E (S-type) conformers, whereas the alpha-L-arabinofuranoside linked to O2 of an internal O-2,3-disubstituted (1-4)-linked beta-D-xylopyranose residue is present in a conformational equilibrium of equal amounts of 4/3T-4E (N-type) and 1E-1/2T (S-type) conformers. Both N- and S-type conformers of the investigated alpha-L-arabinofuranosides contain a rigid C4-O4-C1-O1 segment, assuming for O1 a pseudoaxial orientation and for the exocyclic CH2OH group a pseudoequatorial orientation. From the proton-proton coupling constants the exocyclic rotamer populations could also be determined showing nearly equal preference for the g- and t rotamers.