Absolute configuration of sebiferine

Absolute configuration of sebiferine has been determined.     

Absolute configuration of fucoxanthin

The common natural isomer of the allenic carotenoid fucoxanthin has the 3S,5R,6S,3′S,5′R,6′R configuration.     

Absolute configuration of scyphostatin

[reaction: see text] The absolute configuration of the side chain of scyphostatin (1) has been established. The chemical degradation of 1 gave 4 and 9, which correspond to the C7'-C12' and C13'-C16' fragments of the natural products, respectively. The spectroscopic data and [alpha]D values of both compounds were compared to those of authentic samples. The results show that the absolute configuration of 1 is 8'R,10'S,14'R.     

Stereoselective formation of glycosyl sulfoxides and their subsequent equilibration: ring inversion of an alpha-xylopyranosyl sulfoxide dependent on the configuration at sulfur

A series of four S-allyl D-thiopyranosides, alpha- and beta-manno and xylo, were oxidized with MCPBA at low temperature to give seven of the eight possible sulfoxides, whose configuration at sulfur was determined either directly by X-ray crystallography or by correlation with closely related structures. For the axial thioglycosides oxidation leads very predominantly to the (R)(S)-diastereomer in the xylo series and exclusively so in the manno series; the configuration at C2 is of little importance in determining the stereoselectivity of oxidation of axial thioglycopyranosides. In the equatorial series the configuration at C2 has a significant effect on the outcome of the reaction as, although both series favored the (S)(S)-sulfoxide, selectivity was significantly higher in the case of the beta-mannoside than of the beta-xyloside. The two alpha-xylo sulfoxides have different conformations of the pyranoside ring with the (R)(S)-isomer adopting the (1)C(4) chair and the (S)(S)-diastereomer the (4)C(1). Each pair of diastereomeric sulfoxides was thermally equilibrated in C(6)D(6) and in CD(3)OD. In the mannose series the kinetic isomers are also thermodynamically preferred. In the xylose series, on the other hand, the nature of the thermodynamic isomer in both the alpha- and beta-anomers is a function of solvent with a switch observed on going from C(6)D(6) to CD(3)OD. The results are rationalized in terms of the exo-anomeric effect, steric shielding provided by H3 and H5 in the axial series, the interaction of the C2-O2 and sulfoxide dipoles, and increased steric interactions on hydrogen bonding of the sulfoxides to CD(3)OD.     

Absolute configuration of strictosidinic acid

The absolute configuration of strictosidinic acid, (2S,3R,4S)‐3‐ethenyl‐2‐(β‐d ‐glucopyranosyloxy)‐4‐{[(1S)‐2,3,4,9‐tetrahydro‐1H‐pyrido[3,4‐b]indol‐1‐yl]methyl}‐3,4‐dihydro‐2H‐pyran‐5‐carboxylate, was determined from its sodium chloride trihydrate, poly[[diaqua((2S,3R,4S)‐3‐ethenyl‐2‐(β‐d ‐glucopyranosyloxy)‐4‐{[(1S)‐2,3,4,9‐tetrahydro‐1H‐pyrido[3,4‐b]indol‐2‐ium‐1‐yl]methyl}‐3,4‐dihydro‐2H‐pyran‐5‐carboxylate)sodium] chloride monohydrate], {[Na(C₂₆H₃₂N₂O₉)(H₂O)₂]Cl·H₂O}_n. The strictosidinic acid molecule participates in intermolecular hydrogen bonds of the O—H...O and O—H...Cl types. The solid‐state conformation was observed as a zwitterion, based on a charged pyridine N atom and a carboxylate group, the latter mediating the packing through coordination with the sodium cation.     

Selective oxidation of glycosyl sulfides to sulfoxides using magnesium monoperoxyphthalate and microwave irradiation

A protocol that uses moist magnesium monoperoxyphthalate (MMPP) as an oxidant under microwave irradiation rapidly yields a variety of glycosyl sulfoxides from corresponding sulfides in high yields with high selectivity.     

Stereospecific synthesis of alpha- and beta-C-glycosides from glycosyl sulfoxides: scope and limitations

C-Glycosides derived from alpha-L-fuco-, alpha-D-gluco-, beta-D-gluco-, and alpha-D-mannopyranose have been synthesized from the corresponding glycosyl phenyl sulfoxide through phenylsulfinyl-lithium exchange, to generate an anomeric carbanion, and subsequent reaction with a carbon electrophile. The reactions were stereospecific and proceeded with retention of the configuration at the anomeric center. Improved yields of C-glycosides were obtained by an inverse addition protocol. Trapping of the anomeric carbanion with aldehydes gave best results. Reaction with ketones, chloroformates, nitriles, and alkyl halides was also explored. Mechanistic aspects of the reaction are discussed.     

Absolute configuration and biosynthesis of tiliageine

Tracer experiments on Tiliacora racemosa Colebr established that tiliageine has “S” and “R” configuration at the asymmetric centres C₁ and C'₁ respectively. The experiments also prove that tiliageine is biosynthesised in the plants from N-methylcoclaurine.     

Absolute configuration of 3-acetylbetulinic acid

The absolute configuration of 3-acetoxybetulinic acid is determined by single crystal X-ray diffraction.     

Absolute configuration of vinerine and vineridine

Summary On the basis of an analysis of the circular dichroism and NMR spectra the absolute configuration 7R, 3R, 4S, 15S, 19S, 20S has been established for vinerine; 7S, 3R, 4S, 15S, 19S, 20S for vineridine; and 7S, 3S, 4R, 15S, 19S, 20S for N-acetylvinerine.Institute of the Chemistry of Plant Substances, Academy of Sciences of the Uzbek SSR. Translated from Khimiya Prirodnykh Soedinenii, No. 4, pp. 493–502, July–August, 1974.     

Absolute configuration of (−)-solanapyrone A

Absolute configuration of (?)-solanapyrone A was confirmed by the application of CD exciton chirality method to the dibenzoate derivative.