A new biflavonoid from Ochna beddomei.

A new biflavonoid, 2,3-dihydroochnaflavone 7,4',7"-tri-O-methyl ether (1) together with two known biflavonoids namely, 2,3-dihydroochnaflavone (2) and ochnaflavone (3) were isolated from the stem bark of Ochna beddomei. The structures were determined by means of spectral and chemical studies.

Flavones from Andrographis viscosula.

Two new 2'-oxygenated flavones, 5,7,2'-trimethoxyflavone (1). and 5,7,2',4',6'-pentamethoxyflavone (2). were isolated from the whole plant of Andrographis viscosula along with three known flavones, echioidinin (3). 5,2',6'-trihydroxy-7-methoxyflavone (4). and echioidin (5). The structures of these compounds were elucidated on the basis of 1D and 2D NMR spectral studies.

Biflavonoids from Ochna afzelii.

The stem bark of Ochna afzelii furnished three biflavonoids among which two are new. Their structures were established from spectroscopic and chemical evidences.

Androechin, a new chalcone glucoside from Andrographis echioides.

A new chalcone glucoside, androechin, and a known flavone glucoside, echioidinin 5-O-glucoside, were isolated from the whole plant of Andrographis echioides. Androechin was characterized as 2,2',6'-trihydroxy-4'-methoxychalcone 2'-O-beta-D-glucopyranoside by spectral and chemical studies.

Solution structure of microcin J25, the single macrocyclic antimicrobial peptide from Escherichia coli.

The three-dimensional solution structure of microcin J25, the single cyclic representative of the microcin antimicrobial peptide class produced by enteric bacteria, was determined using two-dimensional 1H NMR spectroscopy and molecular modeling. This hydrophobic 21-residue peptide exhibits potent activity directed to Gram-negative bacteria. Its primary structure, cyclo(-V1GIGTPISFY10GGGAGHVPEY20F-), has been determined previously [Blond, A., Péduzzi, J., Goulard, C., Chiuchiolo, M. J., Barthélémy, M., Prigent, Y., Salomón, R.A., Farías, R.N., Moreno, F. & Rebuffat, S. (1999) Eur. J. Biochem., 259, 747-755]. Conformational parameters (3JNHCalphaH coupling constants, quantitative nuclear Overhauser enhancement data, chemical shift deviations, temperature coefficients of amide protons, NH-ND exchange rates) were obtained in methanol solution. Structural restraints consisting of 190 interproton distances inferred from NOE data, 11 phi backbone dihedral angle and 9 chi1 angle restraints derived from the coupling constants and three hydrogen bonds in agreement with the amide exchange rates were used as input for simulated annealing calculations and energy minimization in the program XPLOR. Microcin J25 adopts a well-defined compact structure consisting of a distorted antiparallel beta sheet, which is twisted and folded back on itself, thus resulting in three loops. Residues 7-10 and 17-20 form the more regular part of the beta sheet. The region encompassing residues Gly11-His16 consists of a distorted beta hairpin, which divides into two small loops and is stabilized by an inverse gamma turn and a type I' beta turn. The reversal of the chain leading to the Phe21-Pro6 loop results from a mixed beta/gamma turn. A cavity, in which the hydrophilic Ser8 side-chain is confined, is delimited by two crab pincer-like regions that comprise residues 6-8 and 18-1.

Two new 2'-oxygenated flavones from Andrographis elongata.

Two new 2'-oxygenated flavones, 5,2',6'-trihydroxy-7-methoxyflavone (3) and skullcapflavone I 2'-O-beta-D-(4"-E-cinnamyl) glucopyranoside (5), together with three known flavones, 7-O-methylwogonin (1), skullcapflavone I (2) and skullcapflavone I 2'-O-beta-D-glucopyranoside (4) were isolated from the whole plant of Andrographis elongata, and the structures were elucidated by FAB-MS and one- and two-dimensional (1D- and 2D)-NMR spectral studies including 1H-1H correlation spectroscopy (COSY), heteronuclear single quantum coherence (HSQC), heteronuclear multiple bond connectivity (HMBC) and rotating frame Overhauser enhancement spectroscopy (ROESY) experiments, and chemical studies.

16Beta-hydroxy-5alpha-cholestane-3,6-dione, a novel cytotoxic oxysterol from the red alga Jania rubens.

A new cytotoxic oxysterol, 16beta-hydroxy-5alpha-cholestane-3,6-dione was isolated from the red alga Jania rubens. Its structure was established by spectroscopic method. The ID50 value was 0.5 microg/mL.

7-O-Methyltetrahydroochnaflavone, a new biflavanone from Ochna beddomei.

7-O-Methyltetrahydroochnaflavone (1), a new biflavanone, together with nine known flavonoids, afrormosin (2), 2,3-dihydroochnaflavone 7-O-methyl ether (3), kaempferol (4), 2,3-dihydroochnaflavone (5), ochnaflavone (6), (-)-epicatechin (7), kaempferol 3-O-rhamnoside (8), taxifolin 3-O-rhamnoside (9), and kaempferol 3-O-glucoside (10), were isolated from the leaves of Ochna beddomei, and the structures were elucidated by spectral and chemical studies.

A biflavanone from Cycas beddomei.

A new biflavanone, 7,7"-di-O-methyltetrahydrohinokiflavone together with tetrahydrohinokiflavone were isolated from the stems of Cycas beddomei. The structures were established on the basis of spectral and chemical studies.

The cyclic structure of microcin J25, a 21-residue peptide antibiotic from Escherichia coli.

Microcin J25 (MccJ25) is the single representative of the immunity group J of the microcin group of peptide antibiotics produced by Enterobacteriaceae. It induces bacterial filamentation in susceptible cells in a non-SOS-dependent pathway [R. A. Salomon and R. Farias (1992) J. Bacteriol. 174, 7428-7435]. MccJ25 was purified to homogeneity from the growth medium of a microcin-overproducing Escherichia coli strain by reverse-phase HPLC. Based on amino acid composition and absolute configuration determination, liquid secondary ion and electrospray mass spectrometry, extensive two-dimensional NMR, enzymatic and chemical degradations studies, the structure of MccJ25 was elucidated as a 21-residue peptide, cyclo(-Val1-Gly-Ile-Gly-Thr- Pro-Ile-Ser-Phe-Tyr-Gly-Gly-Gly-Ala-Gly-His-Val-Pro-Glu-Tyr-Phe21- ). Although MccJ25 showed high resistance to most of endoproteases, linearization by thermolysin occurred from cleavage at the Phe21-Val1 bond and led to a single peptide, MccJ25-L. While MccJ25 exhibited remarkable antibiotic activity towards Salmonella newport and several E. coli strains (minimal inhibitory concentrations ranging between 0.01 and 0.2 microgram.mL-1), the thermolysin-linearized microcin showed a dramatic decrease of the activity, indicating that the cyclic structure is essential for the MccJ25 biological properties. As MccJ25 is ribosomally synthesized as a larger peptide precursor endowed with an N-terminal extremity, the present study shows that removal of this extension and head-tail cyclization of the resulting propeptide are the only post-translational modifications involved in the maturation of MccJ25, that appears as the first cyclic microcin.

Calodenin C: a new guibourtinidol-(4alpha-->8)-afzelechin from Ochna calodendron.

A new dimeric proanthocyanidin, calodenin C [guibourtinidol-(4alpha-->8)-afzelechin], was isolated from the stem bark of Ochna calodendron and its structure determined on the basis of chemical studies and spectroscopic data, including HMBC and ROESY experiments.

Mucronine J a 14-membered cyclopeptide alkaloid from Zizyphus mucronata.

From the CH2Cl2 extract of the root bark of Z. mucronata (Rhamnaceae), a new cyclopeptide alkaloid, named mucronine J, was isolated together with previously known alkaloids abyssenine A and mucronine D. The structure of mucronine J was elucided by mass spectrometry and 1D and 2D NMR. A solution conformation is proposed on the basis of NOE experiments in combination with MM2 calculations.