Search results for "SoMe"
showing 10 items of 5114 documents
13C NMR of carbonyl compounds. 3. Structure and dynamics of protonated enones and dienones
1984
Abstract The unsaturated ketones 1 1 – 10 10 were protonated at low temperatures and studied by dynamic 13C NMR spectroscopy. Four interconverting stereoisomers were detected which differ in their conformation with respect to the CO and CC (enone) single bond.
Rotational Isomerism in Acetic Acid: The First Experimental Observation of the High-Energy Conformer
2003
The high-energy conformer of acetic acid (cis-AA) is produced in an Ar matrix by vibrational excitation of the OH stretching overtone of the ground conformational state (trans-AA). IR-absorption spectroscopy provides a clear identification of the reaction product. cis-AA converts back to trans-AA in a time scale of minutes at 8 K by tunneling. http://dx.doi.org/10.1021/ja038341a
Terphenyl Derivatives from Allantophomopsis lycopodina.
2016
Three secondary fungal metabolites 1–3 with a benzo[b]naphtho[2,1-d]furan skeleton were isolated from submerged cultures of the ascomycete Allantophomopsis lycopodina. The NMR-based structure elucidation was challenging due to a low H/C ratio of only 0.64 and 0.68, respectively. NMR measurements in two different solvents and the use of NMR experiments such as HSQC-TOCSY and LR-HSQMBC proved to be helpful in this respect. The proposed structures obtained from the comprehensive analysis of the NMR data were verified by comparison of recorded and computed NMR chemical shifts from quantum chemical calculations of several constitutional isomers and were further analyzed with the aid of the DP4 a…
Stereoselective Synthesis of (+)-11βH,13-Dihydroestafiatin, (+)-11βH,13-Dihydroludartin, (−)-Compressanolide, and (−)-11βH,13-Dihydromicheliolide fro…
2002
Starting from 2 and 3, obtained from santonin (1), we have synthesized natural guaianolides 4-7. Chemoselective epoxidation of 2 gave (+)-11betaH,13-dihydroestafiatin (4), and epoxidation of 3 followed by regioselective elimination of the hydroxyl group afforded (+)-11betaH,13-dihydroludartin (5). Sharpless' mild regioselective ring-opening of 4 and 5 followed by hydrogenolysis yielded (-)-compressanolide (6) and (-)-11betaH,13-dihydromicheliolide (7), respectively.
Tetrandrine and Isotetrandrine, Two Bisbenzyltetrahydroisoquinoline Alkaloids from Menispermaceae, with Rat Uterine Smooth Muscle Relaxant Activity
1992
Abstract The effects of two bisbenzyltetrahydroisoquinoline alkaloids, 1S, 1′S tetrandrine and its isomer 1R, 1′S isotetrandrine, were investigated in rat isolated uterus in order to identify the mechanism of relaxant action and to study the influence of the absolute configuration on the activity of these alkaloids. Both inhibited the uterine contraction induced by high K+, acetylcholine and oxytocin. In Ca2+-free medium, isotetrandrine relaxed the sustained contraction induced by oxytocin but tetrandrine did not. The relaxant effects of the alkaloids may be due to blockade of calcium influx through specific channels. Tetrandrine and isotetrandrine modify the calcium channel in a nonreversi…
Steroidal saponins from Chlorophytum deistelianum.
2016
Abstract Phytochemical investigation of the aerial parts of Chlorophytum deistelianum led to the isolation of four previously undescribed steroidal saponins called chlorodeistelianosides A–D with five known ones. Their structures were established mainly by extensive 1D and 2D NMR spectroscopic techniques and mass spectrometry as (25R)-3β-[(β- d -glucopyranosyl-(1 → 3)-[α- l -rhamnopyranosyl-(1 → 4)]-β- d -xylopyranosyl-(1 → 3)-[β- d -glucopyranosyl-(1 → 2)]-β- d -glucopyranosyl-(1 → 4)-β- d -galactopyranosyl)oxy]-5α-spirostan-12-one, (24S,25S)-24-[(β- d -glucopyranosyl)oxy]-3β-[(β- d -glucopyranosyl-(1 → 2)-[β- d -xylopyranosyl-(1 → 3)]-β- d -glucopyranosyl-(1 → 4)-β- d -galactopyranosyl)ox…
Triterpenoid saponins from Hydrocotyle bonariensis Lam
2011
Abstract Phytochemical investigation of the under-ground parts of Hydrocotyle bonariensis led to the isolation of five oleanane-type triterpenoid saponins, 3- O -{β- d -glucopyranosyl-(1 → 2)-[α- l -arabinopyranosyl-(1 → 3)]-β- d -glucuronopyranosyl}-21- O -(2-methylbutyroyl)-22- O -acetyl-R 1 -barrigenol, 3- O -{β- d -glucopyranosyl-(1 → 2)-[α- l -arabinopyranosyl-(1 → 3)]-β- d -glucuronopyranosyl}-21- O -(2-methylbutyroyl)-28- O -acetyl-R 1 -barrigenol, 3- O -{β- d -glucopyranosyl-(1 → 2)-[α- l -arabinopyranosyl-(1 → 3)]-β- d -glucuronopyranosyl}-21- O -acetyl-R 1 -barrigenol, 3- O -{β- d -glucopyranosyl-(1 → 2)-[α- l -arabinopyranosyl-(1 → 3)]-β- d -glucuronopyranosyl}-R 1 -barrigenol, a…
Triterpene saponins from Billia rosea.
2017
Five previously undescribed triterpene saponins, billiosides A-E, and a known analogue, were isolated from the seeds of Billia rosea (Planch. & Linden) C. Ulloa & P. Jorg. Their structures were elucidated on the basis of extensive 1D and 2D NMR experiments (1H, 13C, DEPT, COSY, TOCSY, NOESY, ROESY, HSQC, and HMBC) and mass spectrometry as (3β,21β,22α)-3-[(2-O-β-D-glucopyranosyl-O-[α-L-arabinopyranosyl-(1 → 4)]-β-D-glucopyranosyl)oxy]-21-[((2E,6S)-2,6-dimethyl-6-hydroxyocta-2,7-dienoyl)oxy]-22-(acetyloxy)-24-hydroxyolean-12-en-28-oic acid, (3β,21β,22α)-3-[(2-O-β-D-galactopyranosyl-β-D-glucopyranosyl)oxy]-21,22-dihydroxyolean-12-en-28-yl O-α-L-arabinopyranosyl-(1 → 4)-β-D-glucopyranoside, (3β…
Joziknipholones A and B: The First Dimeric Phenylanthraquinones, from the Roots ofBulbine frutescens
2007
From the roots of the African plant Bulbine frutescens (Asphodelaceae), two unprecedented novel dimeric phenylanthraquinones, named joziknipholones A and B, possessing axial and centrochirality, were isolated, together with six known compounds. Structural elucidation of the new metabolites was achieved by spectroscopic and chiroptical methods, by reductive cleavage of the central bond between the monomeric phenylanthraquinone and -anthrone portions with sodium dithionite, and by quantum chemical CD calculations. Based on the recently revised absolute axial configuration of the parent phenylanthraquinones, knipholone and knipholone anthrone, the new dimers were attributed to possess the P-co…
Electronic structure and energy decomposition analyses as a tool to interpret the redox potential ranking of naphtho-, biphenyl- and biphenylenequino…
2016
By calling on modelling approaches we have performed a comparative study on the redox properties of various naphtho-, biphenyl- and biphenylene-quinone isomers. These different compounds exhibit as a whole a redox potential range between 2.09 and 2.90 V vs. Li+/Li. A specific methodology was used to decrypt the interplay among isomerism, aromaticity and antiaromaticity modifications and the stabilization/destabilization effects due to other molecular components on this key electrochemical feature for electrode materials of batteries. In particular, energy decomposition analysis, within the Quantum Theory of Atoms in Molecules, along with the electron and electron spin population changes upo…