A novel stereospecific reduction of alkynes to alkenes

Zinc-copper couple in boiling methanol reduces alkynes to olefins in nearly quantitative yields. Terminal acetylenes are converted to terminal ethylenes, whereas disubstituted acetylenes are transformed to (Z)-olefins.     

Crassiflorone, a new naphthoquinone from Diospyros crassiflora (Hien)

A new naphthoquinone, 11-hydroxy-1,9-dimethyl-6H-naphtho[2′,3′:4,5]furo[3,2-c]chromene-6,7,12-trione, named crassiflorone, was isolated from the stem bark of Diospyros crassiflora together with the known compounds plumbagin, cyclocanaliculatin, gerberinol, lupeol, lupenone and betulinic acid. The structures of the compounds were established on the basis of 1D and 2D NMR spectroscopic data, as well as co-TLC with authentic samples. Some of the above compounds exhibited significant antimicrobial activity against bacteria and yeasts.     

Biogenetic-type synthesis of vepridimerines A–D

A simple synthesis of vepridimerines A–D based on thermolysis of veprisine is presented. In addition, the structure of a novel synthetic veprisine dimer is reported. Since veprisine has been previously synthesized, this report constitutes the first total synthesis of the vepridimerines.     

Evodulone,a new tetranortriterpenoid from carapa procera

Hexane extraction of the ground seeds of $\text{Carapa procera}$ followed by chromatography afforded a new tetranortritepenoid for which the structure (II) is proposed on the basis of spectroscopic evidence.     

Application of matrix-assisted laser desorption/ionization to on-line aerosol time-of-flight mass spectrometry

Matrix-assisted laser desorption/ionization (MALDI) mass spectra were obtained from single biological aerosol particles using an aerosol time-of-flight mass spectrometer (ATOFMS). The inlet to the ATOFMS was coupled with an evaporation/condensation flow cell that allowed the aerosol to be coated with matrix material as the sampled stream entered the spectrometer. Mass spectra were generated from aerosol composed either of gramicidin-S or erythromycin, two small biological molecules, or from aerosolised spores of Bacillus subtilis var niger. Three different matrices were used: 3-nitrobenzyl alcohol, picolinic acid and sinapinic acid. A spectrum of gramicidin-S was generated from approximately 250 attomoles of material using a molar ratio of 3-nitrobenzyl alcohol to analyte of approximately 20:1. A single peak, located at 1224 Da, was obtained from the bacterial spores. The washing liquid and extract solution from the spores were analyzed using electrospray mass spectrometry and subsequent MS/MS product ion experiments. This independent analysis suggests that the measured species represents part of the B. subtilis peptidoglycan. The on-line addition of matrix allows quasi-real-time chemical analysis of individual, aerodynamically sized particles, with an overall system residence time of less than 5 seconds. These results suggest that a MALDI-ATOFMS can provide nearly real-time identification of biological aerosols. Copyright 2000 John Wiley & Sons, Ltd.     

Quinovic acid glycosides from Mitragyna stipulosa--first examples of natural inhibitors of snake venom phosphodiesterase I

Phytochemical investigations on the non-alkaloidal extracts of Mitragyna stipulosa bark has led to the isolation of a series of triterpenoids mainly consisting of quinovic acid ([structure: see text]) and its glycoside derivatives [structure: see text] and [structure: see text]. The other constituents isolated include alpha-amyrin, 3beta-acetyl ursolic acid and a mixture of oleanolic and ursolic acid and beta-sitosterol glucopyranoside. Their structures were identified by spectral and chemical studies and compounds [structure: see text] and [structure: see text] were, respectively, identified as quinovic acid 3-O-[beta-D-glucopyranoside] (quinovin glycoside C) and quinovic acid 3-O-[beta-D-quinovopyranoside]-27-O-[beta-D-glucopyranosyl] ester. Compounds [structure: see text] and [structure: see text] showed significant inhibitory activity against snake venom phosphodiesterase I.     

Carapolide A,A novel hexanortriterpenoid and carapolides b and c,novel tetranortriterpenoids from the seeds of carapaprocera (meliaceae)

Carapolide A, a novel hexanortriterpenoid, and carapolides B and C, novel tetranortriterpenoids have been isolated from the seeds of $\text{Carapa}$$\text{procera}$ and have been assigned structures (2), (10) and (11) respectively on the basis of chemical and spectroscopic evidence.     

Electrochemical behavior and in-vitro antimicrobial screening of some thienylazoaryls dyes

Background

A series of recently reported phenolic azo dyes 7a–e were prepared by coupling the thienyl diazonium sulfate of 3-Amino-4H-benzo[f]thieno[3,4-c](2H)chromen-4-one with selected diversely substituted phenolic and naphtholic derivatives. These compounds were evaluated for their antibacterial and antifungal activities. Furthermore their voltammetric behavior was compared at a glassy carbon electrode.

Results

The voltammetric behavior of the five recently reported azo dyes has been compared at a glassy carbon electrode. It is shown that the azo dyes 7a–e with a hydroxyl group in the ortho position with respect to the azo bridge give rise to well defined, irreversible peaks for the oxidation and reduction process within a pH range of 2–7. The mechanisms of electrochemical oxidation of compound 7a–c and 7e are proposed. For the hydroxyl-substituted dyes, re-oxidation peaks were obtained in the subsequent scan. The antimicrobial activities of the reported compounds 7a–e along with the entire precursors 1–4 and 6a–e were performed against selected bacterial and fungal species and their activities compared to those of nystatin, griseofulvin and ciprofloxacin used as reference drugs.

Conclusions

The present study showed significant antimicrobial activity of compounds 6d, 7a and 7c,e against the tested microorganisms; this result confirms the antimicrobial potency of azo compounds and some of their precursors.

     

The structures of vepridimerines A-D,four new dimeric prenylated quinolone alkaloids from Vepris lousii and Oricia renieri (Rutaceae)

Four new isomeric dimeric prenylated quinolone alkaloids, vepridimerines A-D, have been isolated from the bark of Vepris louisii and Oricia renieri (Rutaceae) and have been assigned structures (2)–(5) respectively on the basis of spectroscopic evidence, in particular¹H and¹³C n.m.r. data.