Shi Qixun, Mower Matthew P, Blackmond Donna G, Rebek Julius
Department of Chemistry, Fudan University, Shanghai 200433, China;
Department of Chemistry, The Scripps Research Institute, La Jolla, CA 92037;
Proc Natl Acad Sci U S A. 2016 Aug 16;113(33):9199-203. doi: 10.1073/pnas.1610006113. Epub 2016 Aug 1.
Water-soluble, deep cavitands serve as chaperones of long-chain diesters for their selective hydrolysis in aqueous solution. The cavitands bind the diesters in rapidly exchanging, folded J-shape conformations that bury the hydrocarbon chain and expose each ester group in turn to the aqueous medium. The acid hydrolyses in the presence of the cavitand result in enhanced yields of monoacid monoester products. Product distributions indicate a two- to fourfold relative decrease in the hydrolysis rate constant of the second ester caused by the confined space in the cavitand. The rate constant for the first acid hydrolysis step is enhanced approximately 10-fold in the presence of the cavitand, compared with control reactions of the molecules in bulk solution. Hydrolysis under basic conditions (saponification) with the cavitand gave >90% yields of the corresponding monoesters. Under basic conditions the cavitand complex of the monoanion precipitates from solution and prevents further reaction.
水溶性的深陷穴体充当长链二酯的伴侣，使其在水溶液中进行选择性水解。穴体以快速交换的折叠J形构象结合二酯，这种构象将烃链掩埋，并依次将每个酯基暴露于水介质中。在穴体存在下的酸水解导致单酸单酯产物的产率提高。产物分布表明，由于穴体中的受限空间，第二种酯的水解速率常数相对降低了两到四倍。与分子在本体溶液中的对照反应相比，在穴体存在下第一个酸水解步骤的速率常数提高了约10倍。在碱性条件下（皂化）用穴体进行水解，相应单酯的产率>90%。在碱性条件下，单阴离子的穴体配合物从溶液中沉淀出来，阻止了进一步的反应。
