<?xml version="1.0" encoding="UTF-8"?><xml><records><record><source-app name="Biblio" version="7.x">Drupal-Biblio</source-app><ref-type>17</ref-type><contributors><authors><author><style face="normal" font="default" size="100%">Wen, X A</style></author><author><style face="normal" font="default" size="100%">Sun, H B</style></author><author><style face="normal" font="default" size="100%">Liu, J.</style></author><author><style face="normal" font="default" size="100%">Cheng, K G</style></author><author><style face="normal" font="default" size="100%">Zhang, P</style></author><author><style face="normal" font="default" size="100%">Zhang, L Y</style></author><author><style face="normal" font="default" size="100%">Hao, J</style></author><author><style face="normal" font="default" size="100%">Ni, P Z</style></author><author><style face="normal" font="default" size="100%">Zographos, S E</style></author><author><style face="normal" font="default" size="100%">Leonidas, D D</style></author><author><style face="normal" font="default" size="100%">Alexacou, K M</style></author><author><style face="normal" font="default" size="100%">Gimisis, T.</style></author><author><style face="normal" font="default" size="100%">Hayes, J.M.</style></author><author><style face="normal" font="default" size="100%">Oikonomakos, N G</style></author></authors></contributors><titles><title><style face="normal" font="default" size="100%">{Naturally occurring pentacyclic triterpenes as inhibitors of glycogen phosphorylase: Synthesis, structure-activity relationships, and X-ray crystallographic studies}</style></title><secondary-title><style face="normal" font="default" size="100%">J. Med. Chem.</style></secondary-title></titles><dates><year><style  face="normal" font="default" size="100%">2008</style></year></dates><number><style face="normal" font="default" size="100%">12</style></number><volume><style face="normal" font="default" size="100%">51</style></volume><pages><style face="normal" font="default" size="100%">3540–3554</style></pages><isbn><style face="normal" font="default" size="100%">0022-2623</style></isbn><language><style face="normal" font="default" size="100%">eng</style></language><abstract><style face="normal" font="default" size="100%">Twenty-five naturally occurring pentacyclic triterpenes, 15 of which were synthesized in this study, were biologically evaluated as inhibitors of rabbit muscle glycogen phosphorylase a (GPa). From SAR studies, the presence of a sugar moiety in triterpene saponins resulted in a markedly decreased activity (7, 18-20) or no activity (21, 22). These saponins, however, might find their value as potential natural prodrugs which are much more water-soluble than their corresponding aglycones. To elucidate the mechanism of GP inhibition, we have determined the crystal structures of the GPb-asiatic acid and GPb-maslinic acid complexes. The X-ray analysis indicates that the inhibitors bind at the allosteric activator site, where the physiological activator AMP binds. Pentacyclic triterpenes represent a promising class of multiple-target antidiabetic agents that exert hypoglycemic effects, at least in part, through GP inhibition.</style></abstract></record></records></xml>