corosolic-acid and maslinic-acid

Three new bidesmosidic saponins (1-3) and a new ursane triterpenoid, 2α,3β,11α,23-tetrahydroxyurs-12-en-28-oic acid (4), along with seven known compounds, were isolated from a methanolic extract of the leaves of Symplocos lancifolia. The bidesmosidic saponins were found to possess the same sugar unit part, composed of two β-d-glucose moieties and one α-l-rhamnose moiety, linked to maslinic acid, arjunolic acid, and asiatic acid, respectively. Their structures were elucidated by interpretation of their 1D and 2D NMR spectra and completed by analysis of the HRESIMS data. The antibacterial activity of the isolated triterpenoids was evaluated against Staphylococcus aureus, Enterococcus faecalis, Escherichia coli, and Pseudomonas aeruginosa, and several showed activity against Gram-positive bacteria.

Topics: Anti-Bacterial Agents; Enterococcus faecalis; Escherichia coli; Magnoliopsida; Microbial Sensitivity Tests; Molecular Structure; Nuclear Magnetic Resonance, Biomolecular; Plant Leaves; Pseudomonas aeruginosa; Saponins; Staphylococcus aureus; Triterpenes; Vietnam

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.

Topics: Adenosine Monophosphate; Allosteric Site; Animals; Binding Sites; Crystallography, X-Ray; Glycogen Phosphorylase; Hypoglycemic Agents; Kinetics; Models, Molecular; Muscles; Oleanolic Acid; Pentacyclic Triterpenes; Protein Binding; Protein Conformation; Rabbits; Stereoisomerism; Structure-Activity Relationship; Triterpenes

Bredemolic acid (3) is a naturally occurring 2β,3α-isomer of maslinic acid (1) that is an allosteric site inhibitor of glycogen phosphorylase (GP). A practical synthesis of 3 was accomplished (18% yield) in five steps starting from the readily available 2β,3β-diol 6a. In a similar fashion, 2β,3α-dihydroxyurs-12-en-28-oic acid (4) was synthesized as a natural 2β,3α-isomer of corosolic acid (2). Compounds 3 and 4 exhibited significant inhibitory activity against rabbit muscle GPa with IC(50) values of 6.25 and 1.1 μM, respectively.

Topics: Animals; Glycogen Phosphorylase; Muscles; Oleanolic Acid; Rabbits; Stereoisomerism; Triterpenes