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首页> 外文期刊>Helvetica chimica acta >Optically Active Cyclophane Receptors for Mono- and Disaccharides: The Role of Bidentate Ionic Hydrogen Bonding in Carbohydrate Recognition
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Optically Active Cyclophane Receptors for Mono- and Disaccharides: The Role of Bidentate Ionic Hydrogen Bonding in Carbohydrate Recognition

机译：单糖和双糖的旋光性环糊精受体：双齿离子氢键在碳水化合物识别中的作用

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摘要

A new family of optically active cyclophane receptors for the complexation of mono-and disaccharides in competitive protic solvent mixtures is described. Macrocycles (-)-(R.R,R,R)-1-4 feature preorganized binding cavities formed by four 1,1'-binaphthalene-2,2'-diyl phosphate moieties bridged in the 3,3'-positions by acetylenic or phenylacetylenic spacers. The four phosphodiester groups converge towards the binding cavity and provide efficient bidentate ionic H-bond acceptor sites (Fig.2). Benzyloxy groups in the 7,7'-positions of the 1,1'-binaphthalene moieties ensure solubility of the nanometer-sized receptors and prevent undesirable aggregation. The construction of the macrocyclic framework of the four cyclophanes takes advantage of Pd~0-catalyzed aryl- acetylene cross-coupling by the Sonogashira protocol, and oxidative acetylenic homo-coupling methodology (Schemes 2 and 8-10). Several cleft-type receptors featuring one 1,1'-binaphthalene-2,2'-diyl phosphate moiety were also prepared (Schemes 1,6, and 7). An undesired side reaction encountered during the synthesis of the target compounds was the formation of naptho[b] furan rings from 3-ethynylnaphthalene-2-ol derivatives, proceeding via 5-endo-dig cyclization (Schemes 3-5). Computer-assisted molecular modeling indicated that the macrocycles prefer nonplanar puckered, cyclobutane-type conformations (Figs. 7 and 8). According to these calculations, receptor (-)-(R,R,R,R)-1 has, on average, a square binding site, which is complementary in size to one monosaccharide. The three other cyclophanes (-)-(R,R,R,R)-2-4 feature, on average, wider rectangular cavities, providing a good fit to one disaccharide, while being too large for the complexation of one monosaccharide. This substrate selectivity was fully confirmed in ~1H-NMR binding titrations. The chiroptical properties of the cyclophanes and their nonmacrocyclic precursors were investigated by circular dichroism (CD) spectroscopy. The CD spectra of the acyclic precursors showed a large dependence from the number of 1,1'-binaphthalene moieties (Fig.9), and those of the cyclophanes were remarkably influenced by the nature of the functional groups lining the macrocyclic cavity (Fig. 11). Profound differences were also observed between the CD spectra of linear and macrocyclic tetrakis (1,1'-binaphthalene) scaffolds, which feature very different molecular shapes (Fig. 10). In ~1H-NMR binding titrations with mono- and disaccharides (Fig. 13), concentration ranges were chosen to favor 1:1 host-guest binding. This stoichiometry was experimentally established by the curve-fitting analysis of the titration data and by Job plots. The titration data demonstrate conclusively that the strength of carbohydrate recognition is enhanced with an increasing number of bidentate ionic host-guest H-bonds (Table 1) in the complex formed. As a result of the formation of these highly stable H-bonds, carbohydrate complexation in competitive protic solvent mixtures becomes more favorable. Thus, cleft-type receptors (-)-(R)-7 and (-)-(R)-38 with one phosphodiester moiety form weak 1:1 complexes only in CD_3CN. In contrast, macrocycle (-)-(R,R,R,R)-1 with four phosphodiester groups undergoes stable inclusion complexation with monosaccharides in CD_3CN containing 2% CD_3OD. With their larger number of H-bonding sites, disaccharide substrates bind even more strongly to the four phosphodiester groups lining the cavity of (-)-(R,R,R,R)-2 and complexation becomes efficient in CD_3CN containing 12% CD_3OD. Finally, the introduction of two additional methyl ester residues further enhances the receptor capacity of (-)-(R,R,R,R)-3, and efficient disaccharide complexation occurs already in CD_3CN containing 20% CD_3OD.
机译：描述了用于竞争性质子溶剂混合物中的单糖和双糖络合的新型旋光性环烷受体家族。大环（-）-（RR，R，R）-1-4的特征是预先排列的结合腔，该结合腔是由四个1,1'-联萘-2,2'-磷酸二烷基酯部分在3,3'-位之间通过炔或苯乙炔间隔基。四个磷酸二酯基会聚到结合腔，并提供有效的双齿离子H键受体位置（图2）。 1,1'-联萘部分的7,7'-位的苄氧基确保纳米级受体的溶解性并防止不良的聚集。四个环烷的大环骨架的构建利用了Sonogashira方案中Pd〜0催化的芳基-乙炔的交叉偶联以及氧化炔属均相偶联方法的优势（方案2和8-10）。还制备了几个具有一个1,1'-萘-2,2'-磷酸二基酯部分的裂口型受体（方案1,6和7）。在目标化合物的合成过程中遇到的不希望有的副反应是由3-乙炔基萘-2-醇衍生物形成萘[b]呋喃环，并通过5-endo-dig环化反应进行（方案3-5）。计算机辅助分子建模表明，大环化合物更喜欢非平面褶皱的环丁烷型构象（图7和8）。根据这些计算，受体（-）-（R，R，R，R）-1平均具有正方形结合位点，其大小与一种单糖互补。平均而言，其他三个环烷（-）-（R，R，R，R）-2-4的特征是更宽的矩形腔，可与一种二糖很好地配合，但对于一种单糖的络合而言太大。在〜1H-NMR结合滴定中充分证实了这种底物选择性。通过圆二色性（CD）光谱研究了环烷及其非大环前体的手性。无环前体的CD光谱显示出对1,1'-联萘部分数量的依赖性（图9），而环烷的CD光谱则受到大环腔内衬的官能团性质的显着影响（图9）。 11）。在线性和大环四（1，1'-联萘）支架的CD光谱之间也观察到了深刻的差异，它们的分子形状差异很大（图10）。在单糖和双糖的1H-NMR结合滴定中（图13），选择浓度范围以促进1：1宿主-客体结合。该化学计量是通过滴定数据的曲线拟合分析和乔布图实验确定的。滴定数据最终表明，随着所形成复合物中二齿离子型主客体H键（表1）的增加，碳水化合物识别的强度也得到增强。由于形成了这些高度稳定的氢键，竞争性质子溶剂混合物中的碳水化合物络合变得更加有利。因此，具有一个磷酸二酯部分的裂缝型受体（-）-（R）-7和（-）-（R）-38仅在CD_3CN中形成弱1：1络合物。相反，具有四个磷酸二酯基的大环（-）-（R，R，R，R）-1与单糖在含有2％CD_3OD的CD_3CN中经历稳定的包合复合。由于具有大量H键合位点，二糖底物甚至更牢固地与衬在（-）-（R，R，R，R，R）-2腔中的四个磷酸二酯基团结合，在含12％CD_3OD的CD_3CN中络合变得有效。最后，引入两个额外的甲酯残基进一步增强了（-）-（R，R，R，R，R）-3的受体能力，有效的二糖络合已经在含有20％CD_3OD的CD_3CN中发生。

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