New indanone compounds from Onychium japonicum

A new indanone glucoside pteroside M has been isolated from fronds of Onychium japonicumPteridaceae. The structure of its aglycone pterosin M has been established by ¹³C NMR, PMR spectra and degradation with nitric acid.     

Absolute configurations of pittosporatobiraside A and B from Pittosporum tobira

The absolute configuration at C-12 of pittosporatobiraside A and B isolated from the leaves of Pittosporum tobira was determined to be S on the basis of the exciton chirality of their dibenzoate derivative. The structures of the two glycosides were thus established to be (1S,9S,10S,11S,12S,14R,16R)-12-[(Z)-2-methyl-1-oxo-2-butenyl]-6,14-dimethyl-2-methylene-9-(1-methylethyl)-15,17-dioxatricyclo[8.7.0.0^11,16]heptadec-5-en-13-one and (1S,9S,10S,11S,12S,14R,16R)-12-(3-methyl-1-oxo-2-butenyl)-6,14-dimethyl-2-methylene-9-(1-methylethyl)-15,17-dioxatricyclo [8.7.0.0^11,16]heptadec-5-en-13-one, respectively.     

Flavanone and other constituents from Onychium siliculosum

Two new compounds, onitinoside and onysilin along with the known compounds, pinostrobin, onitin, onitisin, campesterol, sitosterol and n-alkanes (C₂₅-C₃₃) were isolated from Onychium siliculosum. Onitinoside and onysilin were identified by spectral and chemical methods as 4-O-glucosyl-6-(2′-hydroxyethyl)-2,2,5,7-tetramethylindan-1-one and 5-hydroxy-6,7-dimethoxyflavanone, respectively.     

Zur konfiguration des cyanglycosides holocalin

From its behaviour on GLC holocalin possesses the (R)-configuration in the chiral centre of its aglycone; consequently the diastereomeric glycoside zierin belongs to the (S)-series.     

E-2(S)-amino-3-methyl-3-pentenoic acid from coniogramme intermedia

A new amino acid, E-2(S)-amino-3-methyl-3-pentenoic acid was isolated from Coniogramme intermedia. The structure was elucidated by elementary analysis, optical rotation, catalytic hydrogenation, ¹H and ¹³C NMR spectra.     

Absolute configuration of eschscholtzxanthin

The chirality of eschscholtzxanthin (all-trans (3S,3′S)-4′,5′-didehydro-4,5′-retro-β,βcarotene-3,3′-diol) at 3,3′ was assigned from the CD correlation of the natural material and the semi-synthetic carotenoid prepared by (NBS-dehydrogenation of natural zeaxanthin ((3R,3′R)-β,β-carotene-3,3′-diol). The δ^6(6′)-trans configuration followed from ¹H NMR evidence, including nuclear Overhauser experiments with rhodoxanthin, retrodehydro-carotene (4′,5′-didehydro-4,5′-retro-β,β-carotene) and smaller retro model compounds revealing a general preference for the δ⁶-trans configuration in retro compounds. Biosynthetic considerations are made.     

Absolute configuration of four cleistanthane diterpenes from velloziaceae

The absolute configurations of four cleistanthane diterpenes isolated from several species of Vellozia were determined by circular dichroism measurements.     

On the stereochemistry of 2,3-dihydroxy fatty acids. The single crystal structure of potassium d-erythro-2,3-dihydroxyoctadecanoate

The erythro-2,3-dihydroxyoctadecanoic acid studied is a synthetic homologue of a natural occurring constituent of sphingolipids. The potassium salt of the acid crystallizes in the monoclinic space group P2, with the unit cell dimension: $\text{a = 5.39, b = 7.06, c = 26.26}\text{A}\text{?}\text{and}\text{β = 94.9°}$. The crystal structure was solved by direct methods and was refined to R = 0.062. The absolute configuration of the compound was determined by means of anomalous scattering effects, showing that the natural fatty acid has d-erythro configuration. The compound packs tail to tail in an unusual bilayer arrangement. The hydrocarbon chains have an extreme tilt of 60° and opposite inclination in the two halves of the bilayer. Laterally the hydrocarbon chains are arranged according to the monoclinic M∥ packing mode. The carbon chain makes a perpendicular bent at carbon atom 2. This places the 2-hydroxyl group in a preferred co-planar conformation towards the carboxylate group and at hydrogen bond distance to one of the carboxylate oxygens. The carboxylate group and the two hydroxyl groups are co-ordinated to K⁺ ions and together account for a large molecular cross-ection of 38 Ų. Monolayer studies show that the acid forms a phase with this spacious molecular area also in contact with water. On compression above 10 mN m^?1 transition to a more condensed state ($\text{S = 27}\text{A}\text{?}{}^2$) takes place accompanied by marked changes of the surface potential.     

Confertdiolide,a novel sesquiterpenoid lactone from Parthenium

Four sesquiterpene lactones were isolated from several populations of Parthenium confertum var. lyratum (Gray) collected in Sierra de Arteaga, southern Coahuila. Three of the compounds, hysterin, tetraneurin E and hymenin were previously isolated from other Parthenium species. The fourth constituent is the new cyclopropanoid sesquiterpene dilactone confertdiolide which represents a new structural type. The photolytic conversion of hymenin into confertdiolide confirmed its structure.