RESUMEN
An efficient protocol for calculating 13C NMR chemical shifts for natural products with multiple degrees of conformational freedom is described. This involves a multistep procedure starting from molecular mechanics and ending with a large basis set density functional model to obtain accurate Boltzmann conformer weights, followed by empirically corrected density functional NMR calculations for the individual conformers. The accuracy of the protocol (average rms <4 ppm) was determined by application to â¼925 diverse natural products, the structures of which have been confirmed either by X-ray crystallography or independent synthesis. The protocol was then applied to â¼ 2275 natural products, the structures of which were elucidated mainly by NMR and MS data. Five to ten percent of the latter compounds exhibited rms errors significantly in excess of 4 ppm, suggesting possible structural or signal assignment errors. Both data sets are available from an online browser ( NMR.wavefun.com ). The procedure can be and has been fully automated and is practical using present-generation personal computers, requiring a few hours or days depending on the size of the molecule and number of accessible conformers.
Asunto(s)
Productos Biológicos/química , Espectroscopía de Resonancia Magnética con Carbono-13/métodos , Cristalografía por Rayos X , Teoría Funcional de la Densidad , Conformación MolecularRESUMEN
Dehydroacetic acid (1) was found to induce photoisomerization, converting aldrin (3) and dieldrin (4) into photoaldrin (5) and photodieldrin (6), respectively, not only when irradiated with artificial light at wavelengths longer than 290 nm in air but also when exposed to sunlight in air. By contrast, sodium dehydroacetate (2) induced both photoisomerization, primarily converting 3 to 5 and photoepoxidation, partially forming 6. Thus, because 2 is usually used as a water-soluble antiseptic, photo-erethism might occur due to the isomerization and epoxidation properties of this compound. The difference between the photoreactivity of 1 and that of 2 might be attributed to the spin density of the odd electron on the carbon atom in the respective radicals that were formed after photo-excited 1 and 2 caused H-abstraction.
Asunto(s)
Antiinfecciosos Locales/química , Cosméticos/química , Pironas/química , Radicales Libres/química , Estructura Molecular , Procesos Fotoquímicos , Teoría CuánticaRESUMEN
Although extensive studies have done much to clarify the molecular mechanisms of osteoclastogenesis during the last ten years, there may still be unknown molecules associated with osteoclast differentiation. Thus, we used fluorescent differential display to screen for genes whose expression is induced by receptor activator of NF-κB ligand (RANKL), a crucial molecule for osteoclast formation. We identified caveolin-1 (Cav-1) as a RANKL-induced gene. Cav-1 is a major structural protein of caveolae and lipid rafts, cholesterol-enriched microdomains in the plasma membrane (PM). The RANKL-induced Cav-1 was immediately conveyed to lipid rafts. Conversely, expression of flotillin-1 (Flot-1), another scaffolding protein of lipid rafts, was reduced during osteoclastogenesis, indicating conversion of Flot-1-predominant rafts into Cav-1-enriched rafts. However, in vitro osteoclastogenesis of precursor cells from Cav-1-null mice was comparable to that of wild-type mice, while Cav-2 expression in the knockout osteoclasts was maintained. Conversely, Cav-2 gene silencing in Cav-1-null osteoclast precursors using siRNA for Cav-2 increased osteoclast formation, suggesting that the Cav-1/Cav-2 complex may act as a negative regulator for osteoclastogenesis. On the other hand, destruction of lipid rafts by removal of cholesterol from the PM by methyl-ß-cyclodextrin (MCD) treatment caused disordered signal transductions for osteoclastogenesis, such as hyperactivation of Erk1/2 and insensitivity of Akt to RANKL stimulus. The abnormal signaling was reproduced by deleting exogenous lipoproteins from the culture medium, which also resulted in reduced osteoclast formation. In addition, the deletion caused delayed expression of nuclear factor of activated T cells c1 (NFATc1), and depressed its activation in the cytosol and inhibited its translocation into nuclei. Simultaneously, the deletion reduced the level of FcRγ, a trigger protein for initiating the calcium signaling needed to activate NFATc1, and decreased Cav-1 in lipid rafts. These findings indicate that the molecular mechanisms of osteoclastogenesis are highly dependent on extracellular lipoprotein and the integrity of lipid rafts, and suggest possible involvement of cholesterol.