Revised absolute stereochemistry of rhodiolosides A-D, rhodiolol A and sachalinol A from Rhodiola rosea

The absolute stereochemistry of rhodiolosides A-D (1-4), four monoterpene glycosides from the roots of Rhodiola rosea, and their aglycones, rhodiolol A (5), (-)-rosiridol (6) and sachalinol A (7), were reinvestigated. It was found that the absolute configurations of C-4 in these compounds, previously assigned to be 4-R, should be revised to 4-S.     

Absolute structures of new megastigmane glycosides, foliasalaciosides E(1), E(2), E(3), F, G, H, and I from the leaves of Salacia chinensis

Following the investigation of foliasalaciosides A(1), A(2), B(1), B(2), C, and D, seven new megastigmane glycosides named foliasalaciosides E(1)-I (1-7), together with four known constituents, were isolated from the leaves of Salacia chinensis LINN. collected in Thailand. The absolute stereostructures of the new compounds were characterized on the basis of chemical and physicochemical evidence, including the application of the modified Mosher's method.     

Synthesis of both enantiomers of akolactone B and (+)-ancepsenolide

The syntheses of (+)- and (−)-akolactone B and (+)-ancepsenolide were accomplished using a Pd-catalyzed carbonylation. As to the absolute configuration of akolactone B, making a comparison of the specific rotation of both enantiomers of synthetic akolactone B and the natural compound suggests that the absolute configuration at the 4-position of akolactone B is (R).     

Medicinal foodstuffs. XIX. Absolute stereostructures of canavalioside, a new Ent-kaurane-type diterpene glycoside, and gladiatosides A1, A2, A3, B1, B2, B3, C1, and C2, new acylated flavonol glycosides, from sword bean, the seeds of Canavalia gladiata

A new ent-kaurane-type glycoside, canavalioside, and eight new acylated flavonol glycosides, gladiatosides A1, A2, A3, B1, B2, B3, C1, and C2, were isolated from the seed of Canavalia gladiata together with robinin, kaempferol 3-O-beta-D-galactopyranosyl-7-O-alpha-L-rhamnopyranoside, and kaikasaponin III. The absolute stereostructures of canavalioside and gladiatosides A1, A2, B1, B2, B3, C1, and C2 were elucidated on the basis of chemical and physicochemical evidence.     

Tricalysiosides P-U: Ent-kaurane glucosides and a labdane glucoside from leaves of Tricalysia dubia OHWI

Further extensive isolation work on the 1-BuOH-soluble fraction of a MeOH extract of Tricalysia dubia afforded five new ent-kaurane glucosides (4-8) and one new labdane glucoside (9), together with a known megastigmane glucoside, sammangaoside B (1), and monoterpene glucosides (2, 3). The structures of the new compounds were elucidated by analyses of one- and two-dimensional NMR spectroscopic data. The absolute configuration of the 9-position of sammangaoside B was revised to S and its total stereochemistry was established by the modified Mosher's method.     

Myrseguinosides A-E, five new glycosides from the fruits of Myrsine seguinii

Chemical investigation of the 1-BuOH soluble fraction of the dried fruits of Myrsine seguinii (Myrsinaceae) led to the isolation of five new glycosides, named myrseguinosides A-E (1-5), together with eight known compounds (6-13). The absolute structures of the new glycosides were elucidated by spectroscopic and chemical analyses to be a monoterpene glucoside (1), two flavonol glycosides (2, 3), and two oleanane-type triterpene saponins (4, 5). Myrseguinosides B (2), D (4), and E (5) exhibited 1,1-diphenyl-2-picrylhydrazyl (DPPH) radical-scavenging activity and growth inhibitory activity toward human cancer cells, respectively.     

Rogioldiol A,a new obtusane diterpene,and rogiolal,a degraded derivative,of the red seaweed Laurencia microcladia from II rogiolo along the coast of tuscany: A Synergism in Structural Elucidation

The structure of rogioldiol A ((?)- 1 ), isolated from the red seaweed Laurencia microcladia, was determined. Employing the exciton-coupling technique for rogioldiol A p-bromobenzoate ( 2 ), the absolute configuration at C(9) of (?)- 1 was assigned, and, together with extensive NMR experiments, the absolute configuration at C(10) and preferred conformations of (?)- 1 were determined. The absolute configuration of the hetero-substituted cyclohexane ring was deduced in analogy from the X-ray structure of 4 , a derivative of the aldehyde 3 , which was isolated from the same seaweed and is believed to be a degradation product of (?)- 1 .     

Two New Megastigmane Glycosides and a New Iridoid Glycoside from Gelsemium elegans

Two new megastigmane glycosides, eleganosides A and B ( 1 and 3 , resp.), and one new iridoid glycoside, gouwenoside A ( 4 ), together with two known compounds, foliasalacioside B₁ ( 2 ) and loganin ( 5 ), were isolated from the aerial parts of Gelsemium elegans (Gardn. et Champ.) Benth. (Loganiaceae). Their structures were elucidated by spectroscopic methods including 1D‐ and 2D‐NMR techniques. The absolute configuration of 1 was determined by CD spectroscopy.     

Determination of absolute stereochemistry of natural alicyclic glycosides by 1H NMR spectroscopy without application of chiral reagents--an indication

A study has been made of the 1H NMR spectra of peracetylated beta-glucopyranosides and alpha-arabinopyranosides obtained by reaction of D- and L-glucoses, and L- and D-arabinoses with either (R)- or (S)-2-octanols. The obtained and literature data show that 1H NMR spectra may be used to determine the absolute configuration of the aglycone moieties of some alicyclic glycosides without the need to synthesize derivatives with chiral reagents, as long as the absolute configuration of their monosaccharide moiety is known or vice versa. Spectra of marine steroid glycosides and their acetates containing glycosylated side chains as alicyclic fragments were also examined. It was shown that analysis of 1H NMR spectra for the determination of the absolute configuration is more applicable in the cases when glycosides have the same substitution in the D-ring of the aglycone moiety.     

Medicinal flowers. XXI. Structures of perennisaponins A, B, C, D, E, and F, acylated oleanane-type triterpene oligoglycosides, from the flowers of Bellis perennis

Six new acylated oleanane-type triterpene oligoglycosides, perennisaponins A (1), B (2), C (3), D (4), E (5), and F (6), were isolated from the flowers of Bellis perennis (Daisy flower) together with 14 saponins, nine flavonoids, and two glycosides. The structures of 1-6 were elucidated on the basis of chemical and physicochemical evidence.     

Selectivity of biohydroxylation with Beauveria bassiana of trans-2-fluorocycloalkyl N-phenylcarbamates

Biohydroxylation with Beauveria bassiana of racemates and the pure enantiomers of trans-2-fluorocyclohexyl- 3 and trans-2-fluorocycloheptyl N-phenylcarbamates 6 were investigated and compared with results found for the corresponding nonfluorinated parent compounds. In all cases, mixtures of diastereomeric products hydroxylated in the 4-position were isolated, besides products of p-hydroxylation of the aromatic ring and succeeding compounds derived from these primary reaction products. The regioselectivity of hydroxylation by this fungus is not changed by a single fluorine substituent attached closely to the electron-rich anchoring group in the trans-2-position. There is a different influence on the diastereoselectivity of hydroxylation depending on the absolute configuration of the fluorinated substrates. While the transformation of the (S,S)-2-fluorocycloalkyl N-phenylcarbamates is not diastereoselective giving almost 1:1 mixtures of cis- and trans-4-hydroxyl compounds, the corresponding reactions of the (R,R)-isomers led preferentially to the products trans-hydroxylated in the 4-position. The transformation of the racemic fluorinated six-membered N-phenylcarbamate 3 led to products having a very small enantiomeric excess. The fluorine substituent slightly increased the enantioselectivity of transformation of the racemic seven-membered substrate 6 compared to the C(s)()-symmetric nonfluorinated carbamate. Thus, the fluorine substituent in the trans-2-position in these examples did not change the regioselectivity but rather influenced the stereochemistry of biotransformation, depending on the absolute configuration of the substrate and ring size.     

The absolute stereostructures of cyanogenic glycosides, hydracyanosides A, B, and C, from the leaves and stems of Hydrangea macrophylla

Three new cyanogenic glycosides named hydracyanosides A (1), B (2), and C (3) were isolated from the leaves and/or stems of Hydrangea macrophylla in China. The absolute stereostructures of hydracyanosides were characterized on the basis of chemical and physiochemical evidence including single crystal X-ray crystallographic analysis. To the best of our knowledge, this is the first scientific report of cyanogenic glycosides from Hydrangea plants.     

Synthesis and stereochemistry of (−)-rosiridol and (−)-rosiridin

The plant-derived monoterpenoids (−)-rosiridol and (−)-rosiridin can be assembled in an enantioselective manner via DIP-Cl reduction of a ketone precursor obtained by BCl₃-mediated C-C coupling of prenyl stannane and an α,β-unsaturated C₅ aldehyde. On the basis of Mosher analyses, the absolute stereochemistry 4S was assigned to (−)-rosiridol; this was confirmed by X-ray structure analysis of pentaacetylrosiridin. Glucosylation of (4S)-4-acetoxygeraniol proceeds under Koenigs-Knorr conditions in diethyl ether. (−)-Rosiridin was synthesized for the first time.     

Derivatives of vibralactone from cultures of the basidiomycete Boreostereum vibrans

Four new natural products possessing vibralactone skeleton, 1,5-secovibralactone (1), vibralactone B (2), vibralactone C (3) and acetylated vibralactone (4), together with known compound vibralactone (5), had been isolated from cultures of the basidiomycete Boreostereum vibrans. The structures of 1-4 were elucidated on the basis of spectroscopic methods. The absolute configuration of 1 was suggested to be S by computational methods.     

Triterpene and steroid glycosides of theMelilotus genus and their genins I. Melilotosides A,B, and C from the roots ofMelilotus albus

Three new triterpene glycosides of the oleanane series — melilotosides A, B, and C — and the nonglycosylated soyasapogenol B have been isolated from the roots of the plant Melilotus albus Medik. (Leguminosae). The structures of the glycosides have been shown on the basis of chemical transformations and spectral results. Melilotoside A has the structure of soyasapogenol B 3-O-α-L-arabinopyranoside, melilotoside B that of soyasapogenol B 3-O-[O-β-D-galactopyranosyl-(1→2)-α-L-arabinopyranoside], and melilotoside C that of soyasapogenol B 3-O-[O-α-L-rhamnopyranosyl-(1→2)-O-β-D-galactopyranosyl-(1→2)-α-L-arabinopyranoside.     

Two new tremulane sesquiterpenes from a mangrove endophytic fungus,Coriolopsis sp. J5

Two new tremulane sesquiterpenes coriolopsin A (1) and coriolopsin B (2), together with two known ones conocenol C (3) and ceriponol E (4), were isolated from the fermentation extract of endophytic fungus Coriolopsis sp. J5 from Ceriops tagal. The structures and absolute configuration of compounds 1 and 2 were determined based on HR-ESI-MS and spectroscopic data (IR, UV, 1D, 2D NMR and X-ray crystallographic analysis).     

Bioactive constituents from Chinese natural medicines. XXII. Absolute structures of new megastigmane glycosides, sedumosides E1, E2, E3, F1, F2, and G, from Sedum sarmentosum (Crassulaceae)

Six new megastigmane glycosides, sedumosides E1, E2, E3, F1, F2, and G, were isolated from the whole plant of Sedum sarmentosum (Crassulaceae). The structures of new constituents including the absolute configuration were elucidated on the basis of chemical and physicochemical evidence.     

Bioactive constituents of Chinese natural medicines. VII. Inhibitors of degranulation in RBL-2H3 cells and absolute stereostructures of three new diarylheptanoid glycosides from the bark of Myrica rubra

Three new diarylheptanoid glycosides, named (+)-S-myricanol 5-0-beta-D-glucopyranoside, myricanene A 5-O-alpha-L-arabinofuranosyl(1-->6)-beta-D-glucopyranoside, and myricanene B 5-0-alpha-L-arabinofuranosyl(1-->6)-beta-D-glucopyranoside, were isolated from the bark of Chinese Myrica rubra, together with twenty known compounds. The absolute stereostructures of the new diarylheptanoid glycosides were elucidated on the basis of chemical and physicochemical evidence, including the application of the modified Mosher's method. The inhibitory effects of isolated constituents on the release of beta-hexosaminidase from RBL-2H3 cells were examined, and several diarylheptanoids, myricanol, (+)-S-myricanol, myricanone, and myricanenes A and B, and a flavonol, myricetin, were found to show the inhibitory activity.     

Three new phenolic glycosides from the caulis of Millettia speciosa

Three new phenolic glycosides, millettiaspecosides A--C (1-3), were isolated from the caulis of Millettia speciosa along with three known phenolic glycosides, khaephuoside B (4), seguinoside K (5), albibrissinoside B (6). Their structures were established by spectroscopic methods. The spectral analysis permitted correct assignments for (1)H and (13)C NMR data of compounds 4 and 5.     

Synthesis of the core ring system of awajanomycin from N-Boc-3-methoxycarbonyl-2-pyridinone

Awajanomycin, which was isolated from marine-derived fungus, possesses unique structural features and cytotoxic activity against A549 cells. Due to its unique structure, no total synthesis has yet been reported, and neither the relative stereochemistry nor the absolute configuration has been determined. We report the synthesis of the core ring system of awajanomycin, which includes: (i) regioselective addition of the acetate unit onto C4-position of N-Boc-3-methoxycarbonyl-2-pyridinone; (ii) stereoselective installation of a hydroxyl group on C3-position; and (iii) stereo- and regioselective epoxide-opening reaction by Me₃Al.