Antileukaemic quassinoids : structure (X-ray analysis) of bruceine C and revised structure of bruceantinol

The complete structure of bruceine C has been established by single crystal X-ray analysis of the tetra-O-acetyl derivative. The structure of bruceantinol, a potent antileukaemic quassinoid, has been revised and shown to be 4′-O-acetyl bruceine C.     

Longifoamide-A and B: Two new ceramides from Mentha longifolia (Lamiaceae)

Two new N-acylsphingosines (ceramides) named longifoamide A {6'-tetracosenamide, (6'-Z)-N-[2,3-dihydroxy-1-(hydroxymethyl)octadecyl]} and B {6'-tetracosenamide, (6'-Z)-N-[2,3,4-trihydroxy-1-(hydroxymethyl)octadecyl]} were isolated from a methanol extract of Mentha longifolia. Both ceramides were characterized with the aid of 1D and 2DNMR spectroscopic techniques and high resolution mass spectrometry.     

Physico-chemical effects of the major quassinoids in a standardized Eurycoma longifolia extract (Fr 2) on the bioavailability and pharmacokinetic properties, and their implications for oral antimalarial activity

A simple validated LC-UV method for the phytochemical analysis of four bioactive quassinoids, 13alpha(21)-epoxyeurycomanone (EP), eurycomanone (EN), 13alpha,21-dihydroeurycomanone (ED) and eurycomanol (EL) in rat plasma following oral (200 mg/kg) and intravenous administration (10 mg/kg) of a standardized extract Fr 2 of Eurycoma longifolia Jack was developed for pharmacokinetic and bioavailability studies. The extract Fr 2 contained 4.0%, 18.5%, 0.7% and 9.5% of EP, EN, ED and EL, respectively. Following intravenous administration, EP displayed a relatively longer biological half-life (t1/2 = 0.75 +/- 0.25 h) due primarily to its lower elimination rate constant (k(e)) of 0.84 +/- 0.26 h(-1)) when compared with the t1/2 of 0.35 +/- 0.04 h and k(e) of 2.14 +/- 0.27 h(-1), respectively of EN. Following oral administration, EP showed a higher C(max) of 1.61 +/- 0.41 microg/mL over that of EN (C(max) = 0.53 +/- 0.10 microg/mL). The absolute bioavailability of EP was 9.5-fold higher than that of EN, not because of chemical degradation since both quassinoids were stable at the simulated gastric pH of 1. Instead, the higher log K(ow) value of EP (-0.43) contributed to greater membrane permeability over that of EN (log K(ow) = -1.46) at pH 1. In contrast, EL, being in higher concentration in the extract than EP, was not detected in the plasma after oral administration because of substantial degradation by the gastric juices after 2 h. Similarly, ED, being unstable at the acidic pH and together with its low concentration in Fr 2, was not detectable in the rat plasma. In conclusion, upon oral administration of the bioactive standardized extract Fr 2, EP and EN may be the only quassinoids contributing to the overall antimalarial activity; this is worthy of further investigation.     

First comprehensive bakkane approach: stereoselective and efficient dichloroketene-based total syntheses of (+/-)- and (-)-9-acetoxyfukinanolide, (+/-)- and (+)-bakkenolide A, (-)-bakkenolides III,B, C,H, L,V, and X, (+/-)- and (-)-homogynolide A, (+/-)-homogynolide B,and (+/-)-palmosalide C

Cycloaddition of dichloroketene with dimethylcyclohexenes has been used as the key reaction in an efficient, general approach to the bakkanes. New methods and methodologies that have been developed in this work include spiro beta-methylene-gamma-butyrolactonizations, a vicinal dicarboxylation, an angelic ester preparation, a transesterification, an epoxy ketone double reduction, and a retro aldol-aldol approach to low-energy aldol isomers.     

Electron switch in the double-cage fluorinated fullerene anions, e(-)@C20F18(XH)2C20F18 (X = N, B): new candidates for molecular quantum-dot cellular automata

A new type of molecular quantum-dot cellular automata (MQCA) candidates is suggested using the double-cage fluorinated fullerene molecules, e(-)@C(20)F(18)(XH)(2)C(20)F(18) (X = N, B), which have bistable charge configurations that could be used to encode binary information. The electron switch between the two cages leads to the QCA function.     

Syntheses of the C(1-6) and C(19-24) fragments of lituarines A, B, and C

[structure: see text] Lituarines A-C are marine natural products comprising a tricyclic spiroacetal bridged at C(8) and C(18) by a functionalized ester linkage conceptually obtained from a C(19-24) alcohol and a C(1-6) carboxylic acid whose oxidation level varies at C(4) and C(5). Stereoselective routes are described to compounds 26 and 27, fully functionalized ester fragments of lituarine A and lituarines B and C, respectively.     

Enantioselective total syntheses of (+)-arborescidine A, (-)-arborescidine B, and (-)-arborescidine C

Described are the first enantioselective total syntheses of (+)-arborescidine A ((+)-1), (-)-arborescidine B ((-)-2), and (-)-arborescidine C ((-)-3), via routes that proceeded in five steps and 50% overall yield, eight steps and 61% overall yield, and nine steps and 51% overall yield, respectively, from 6-bromotryptamine (7). The syntheses feature the use of the Noyori catalytic asymmetric hydrogen-transfer reaction to introduce chirality in dihydro-beta-carbolines 6 and 8. On the basis of an ample precedent from Noyori's work, the reduction produces dihydro-beta-carbolines, and ultimately the natural products, possessing the R absolute configuration. The synthetic arborescidines displayed optical rotations that were opposite in sign those of the natural products, thereby supporting the S configuration for natural arborescidines A (1) and B (2) and the (3S,17S) configuration for natural arborescidine C (3). Our results are in agreement with the initial stereochemical assignment by Pa?s and co-workers, and are counter to their recently revised assignment.     

Longifoside-A and -B: two new cerebrosides from Mentha longifolia (Lamiaceae)

Two new N-acyl-glycosphingosines (cerebrosides) named longifoside-A {6'-tetracosenamide, N-[3,4-dihydroxy-1-(hydroxymethyl)-2-(beta-D-glucopyranosyl) heptadecyl]-(6'E)} and B {6'-tetracosenamide, N-[3-hydroxy-1-(hydroxymethyl)-2-(beta-D-glucopyranosyl)-4Z-heptadecenyl]-(6'E)} have been obtained from the methanolic extract of Mentha longifolia belonging to the family Lamiaceae. Both the cerebrosides were purified as their acetate-derivatives: 6'-tetracosenamide, N-[3,4-diacetoxy-1-(acetoxymethyl)-2-(tetraacetoxy-beta-D-glucopyranosyl) heptadecyl]-(6'E) and 6'-tetracosenamide, N-[3-acetoxy-1-(acetoxymethyl)-2-(tetraacetoxy-beta-D-glucopyranosyl)-4Z-heptadecenyl]-(6'E). They were characterized with the aid of 1D and sophisticated 2D-NMR spectroscopic techniques.     

Modeling of configurations and third-order nonlinear optical properties of C(36) and C(34)X(2) (X=B,N)

Using the ab initio method, the geometrical structures of C(36) and the X (B,N)-doped isomers C(34)X(2) have been optimized. On the basis of the optimized structures, then, the third-order nonlinear optical polarizabilities gamma in the different optical processes of the third-harmonic generation, electric-field induced second-harmonic generation and degenerate four-wave mixing, and two-photon absorption (TPA) cross sections delta are calculated by using TDB3LYP method coupled with the sum-over-states method. The calculated results show that the one-photon allowed excitation process dominate the two-photon excitation process for C(36)-D(6h), whereas the two-photon allowed excitation process dominate the one-photon excitation process for C(36)-D(2d) and C(34)X(2) (B,N). It is found that the largest resonant TPA peaks of dopant fullerenes have a blueshift and the TPA cross sections have an enhancement compared with those of the parent fullerenes of isomers C(36)-D(6h) and C(36)-D(2d).     

First diastereoselective synthesis of (-)-methyl thyrsiflorin A, (-)-methyl thyrsiflorin B acetate, and (-)-thyrsiflorin C

An efficient procedure for the synthesis of scopadulan diterpenes, using (+)-podocarp-8(14)-en-13-one 13 as starting material, is reported. This procedure has been used for the diastereoselective synthesis of (-)-methyl thyrsiflorin A (8), (-)-methyl thyrsiflorin B acetate (9), and (-)-thyrsiflorin C (7). Key steps in our strategy are the intramolecular cyclopropanation of diazoketone 19 and the regioselective cleavage of the cyclopropane ring.     

Enantiospecific total synthesis of (-)-bakkenolide III and formal total synthesis of (-)-bakkenolides B, C, H, L, V, and X

A concise enantiospecific synthesis of (-)-bakkenolide III was accomplished from (S)-(+)-carvone. The key step involved radical cyclization of an iodoketone intermediate which afforded the cis-hydrindanone skeleton. Further synthetic transformations generated bakkenolide III, which also constitutes the formal total synthesis of (-)-bakkenolides, B, C, H, L, V, and X.     

Search for more stable C58X18 isomers: stabilities and electronic properties of seven-membered ring C58X18 fullerene derivatives (X = H, F, and Cl)

Stimulated by recent preparation and characterization of the first C58F18 fullerene derivative, with a heptagon in the framework (Science, 2005, 309, 278), we have performed systematic density functional studies on the stabilities and electronic properties of two different structures C58X18 (A) and C58X18 (B), where X = H, F, and Cl. The large energy gaps between the highest occupied molecular orbitals and the lowest unoccupied molecular orbitals (between 2.64 and 3.45 eV) and the aromatic character (with nucleus independent chemical shifts from -10.0 to -13.9 ppm) of C58X18 (A) and C58X18 (B) indicate that they possess high stabilities. Further investigations show that the heats of formation of C58X18 fullerene derivatives are highly exothermic, suggesting that adding nine X2's releases much of the strain of pure C58 fullerene and leads to stabilities of the derivatives. Lower in energy and stronger in aromatic character than C58F18 (B), which has been experimentally characterized, C58F18 (A) should also be isolated. In addition, C58F18 and C58Cl18 are predicted to possess large electron affinities, especially for C58F18 (B) and C58Cl18 (B) with values of 3.00 and 3.06 eV, respectively, even larger than that (2.50 eV) of C60F18. Hence, C58F18 and C58Cl18 can serve as good electron-acceptors with possible photonic/photovoltaic application. The IR spectra of C58X18 are simulated to facilitate identification of different isomers experimentally. In addition, the electronic spectra and second-order hyperpolarizabilities of C58X18 are predicted by ZINDO and sum-over-states model. With the addition of 9X2, both the static and frequency-dependent second-order hyperopolarizabilities of C58X18 greatly decrease compared to those of C58.     

Molecular Recognition of Amino Acids by Copper(II) Complexes of 6(A),6(X)-Diamino-6(A),6(X)-dideoxy-beta-cyclodextrin (X = B, C, D)

The three regioisomers of beta-cyclodextrin 6-difunctionalized with NH(2) groups (6(A),6(X)-diamino-6(A),6(X)-dideoxy-beta-cyclodextrin, A,X-CDNH(2), X = B, C, or D) were synthesized. Their binary and ternary copper(II) complexes with amino acids were characterized by ESR and electronic spectroscopy. Furthermore, the binary copper(II) complexes were used as eluent in ligand exchange chromatography (LEC), to resolve racemates of unmodified amino acids. HPLC separation of enantiomers of aromatic amino acids was obtained only when the complex [Cu(A,B-CDNH(2))](2+) was used as eluent. The two complexes with the other two regioisomers did not show chiral recognition ability. Circular dichroism (c.d.) spectroscopy studies of the ternary complexes with D- and L-amino acids carried out in the presence and in the absence of 1-adamantanol, suggested a recognition mechanism that involves the cyclodextrin cavity, only in the case of ternary A,B-CDNH(2) complexes.     

Synthesis,Structure and Properties of C(X)NHP(Y) Fragment Containing Compounds

Abstract

N-(thio)carbonyl(thio)amidophosphate, their open-chain and crown-containing analogues with a C (X) NHP (Y) fragments are associated with intermolecular hydrogen bonds as C=X…H-N and P=Y…H-N or intramolecular hydrogen bonds of N-H…O(macrocycle). These compounds easily enter into alkylation reaction, are added according to C=N bonds of activated imines, take part in O → S and S → O exchanging reactions.     

Theoretical Study on the Structure and Stability of Si4X（X=Li, Be, B, C, N, O, F） Clusters

1 INTRODUCTION Silicon is an important kind of semiconductormaterial having been used to produce many sorts ofapparatus, digital and linear integrated circuit andLarge Scale Integrated circuit (LSI), and its clustershave drawn many scientists’ atten…     

Three novel quassinoids, javanicolides A and B, and javanicoside A, from seeds of Brucea javanica

Two novel quassinoids, javanicolides A and B, and one novel quassinoid glucoside, javanicoside A were isolated from the seeds of Brucea javanica Merr. (Simaroubaceae), along with four known quassinoids, yadanziolides A and D, and bruceins D and E, and two known quassinoid glucosides, yadanziosides D and L. Their structures were elucidated by the analysis of spectral data and chemical evidence.