Structure and chemistry of apicidins, a class of novel cyclic tetrapeptides without a terminal alpha-keto epoxide as inhibitors of histone deacetylase with potent antiprotozoal activities

Apicidins are a class of cyclic tetrapeptides that do not contain the classical electrophilic alpha-keto epoxide yet are potent (nM) inhibitors of histone deacetylase and antiprotozoal agents. These compounds showed broad-spectrum activities against the apicomplexan family of protozoa including Plasmodium sp (malarial parasite), Toxoplasma gondii, Cryptosporidium sp., and Eimeria sp. These cyclic peptides contain a beta-turn amino acid (R)-Pip or (R)-Pro, (S)-N-methoxy Trp, (S)-Ile, or (S)-Val, and either (S)-2-amino-8-oxodecanoic acid or a modified (S)-2-amino-8-oxodecanoic acid. The isolation and structure elucidation of new apicidins from two Fusarium species, temperature-dependent NMR studies of apicidin, NMR and molecular modeling based conformation of the 12-membered macrocyclic ring, and selected chemical modifications of apicidin have been detailed in this paper. The cyclic nature of the peptide, the C-8 keto group, and the tryptophan are all critical for the biological activity.     

Phytochemistry of genus Gentiana, XX. Identification of new di-O-glucosides of C-glucosylflavones in Gentiana asclepiadea l (author's transl)

Phytochemistry of genus Gentiana, XX. Identification of new di-O-glucosides of C-glucosylflavones in Gentiana asclepiadea L. Two new O-glucosides of C-glucoside flavonic compounds [isoorientin-2″,4′-di-O-β-D -glucoside ( 1 ) and isovitexin-2″-4′-O-β-D -glucoside ( 2 )] have been isolated from leaves of Gentiana asclepiadea L . This is the first case of di-O-glucosides of C-glucoside flavones occurring in nature.     

Analysis of t-butylphenol acetylene condensed resin with methyl-methine linkages in vulcanized rubber by pyrolysis-gas chromatography/mass spectrometry

Methyl-methine linkages of Novolac, a commercially available t-butylphenol acetylene condensed (TBPA) resin, have been identified by recognition of pyrolysis pathways using pyrolysis-gas chromatography/mass spectrometry (Py-GC/mS) in vulcanized rubber. The diagnostic mass spectrum of t-butylphenol with methyl-methine linkages between phenolic rings was observed at m/z 192, corresponding to 4-t-butyl-2-ethyl-6-methylphenol. Other molecular ions were observed at m/z 178, 164, and 150 in the characteristic pyrolyzates. The ion at m/z 192 in the TBPA resin was observed to be characteristic for methyl-methine linkages between the phenolic groups, and the analytical pyrolysis-GC/mS method was thus able to identify the resin at low levels in vulcanized rubber. Copyright 1999 John Wiley & Sons, Ltd.     

REDOR Dephasing by Multiple Spins in the Presence of Molecular Motion

Closed-form, numerical algorithms are presented for calculating REDOR dephasing for three general cases: (i) collections of isolatedI–Sspin pairs; (ii) manySspins coupled to anIspin; and (iii) anI–Sspin pair in relative motion. For the case when more than oneSspin is dipolar coupled to anIspin, the calculation assumes that theS–Shomonuclear interaction does not affect REDOR dephasing. Full numerical simulations show that this assumption is true if theS-spin lineshapes are inhomogeneously broadened, theS-spin chemical shifts are far from rotational resonance, and a version of REDOR is used which minimizes the number ofS-spin π pulses. For the rapidly rotating –CF₃group of poly(trifluoroethyl methacrylate), the formalisms of (ii) and (iii) are combined to calculate the dephasing. The experimentally measured dephasing matches theory when the wiggling motion of the –OCH₂CF₃moiety of the polymer is taken into account.     

Analyse des Eisens

Ohne Zusammenfassung     

Reactions of Acetyl Bromide with Lewis Acids. II: Quantitative Raman and PMR Spectrophotometry Study of Halide Exchange in the System TiCI4–CH3COBr

Vapour Pressure Investigations in the System Zn? Si? P Equilibrium pressures on the compounds SiP, Zn₃P₂, and ZnSiP₂ were determined with a Bourdon-Manometer. Corresponding to the decomposition of the compounds the free reaction energies were calculated from the Kp data. Considering Cp-T functions it was possible to determine standard data of the heat of formation and the entropy of SiP, Zn₃P₂, and ZnSiP₂. As a result of our investigations considerations of stability were carried out in the system Zn? Si? P.     

Katalysatorbewertung bei der gleichzeitigen Reduktion von Schwefeldioxid und Stickstoffmonoxid durch Kohlenmonoxid

Ohne Zusammenfassung     

Substituenteneinfluss der phosphino- und der phosphinylgruppe auf die reaktivität aromatischer verbindungen—I : Kinetische untersuchungen des substituenteneinflusses

To get a basis for the molecular-orbital discussion of the effect of phosphino (R₂P) and phosphinyl (R₂P = 0) groups on the reactivity of organic molecules the relative rate constants of four types of reactions are measured by standard kinetic methods. The results show, that both the phosphino and the phosphinyl group increase the rate of alkaline hydrolysis of 4-X-Benzoic-acid-methylester and of aromatic nucleophilic displacement on 4-X-Fluorobenzene, while the rate of methanolysis of 4-X-(α-Chloro-ethyl)-benzene is greater for X = R₂P than for X = H, but smaller for X = R₂PO than for X = H.