Bela Ternai

Advances in Oxazole Chemistry

Publisher Summary This chapter discusses advances in oxazole chemistry. A significant interest in the chemistry of oxazole was revived in an effort to synthesize penicillin, when this fascinating antibiotic molecule was thought to contain an oxazole ring. In this way, aspects of oxazole chemistry are studied which had received little or no attention before. The chapter explores the numerous developments made in the field of oxazole chemistry from the beginning of 1955 to the end of 1972. The emphasis has been placed on methods of synthesis and reactions of the mononuclear oxazoles; therefore, only a few references are given to condensed oxazoles (such as benzoxazoles and naphthoxazoles). The formation of oxazoles generally predominates at around 130oC when slightly more than a molar quantity of formamide is used. The oxazole synthesis is about equally successful when α-halo ketones are boiled with a mixture of ammonium formate and formic acid (large excess) in place of formamide and concentrated sulfuric acid.

Inhibition of wheat embryo calcium-dependent protein kinase and other kinases by mangostin and γ-mangostin

The hull of the fruit of the mangosteen tree (Garcinia mangostana) contains four inhibitors of plant Ca(2+)-dependent protein kinase. Two of these inhibitors have been purified and identified as the xanthones 1,3,6-trihydroxy-7-methoxy-2,8-bis(3-methyl-2-butenyl)-9H- xanthen-9-one (mangostin) and 1,3,6,7-tetrahydroxy-2,8-bis(3-methyl-2-butenyl)- 9H-xanthen-9-one (gamma-mangostin). Both xanthones also inhibit avian myosin light chain kinase and rat liver cyclic AMP-dependent protein kinase. This is the first report of inhibition of plant and animal second messenger-regulated protein kinases by plant-derived xanthones.

Ammonium 4-chloro-7-sulfobenzofurazan: A new fluorigenic thiol-specific reagent

Abstract This paper describes the synthesis and study of a new fluorigenic, thiol-specific reagent, ammonium 4-chloro-7-sulfobenzofurazan, which is readily prepared by sulfonation of 4-chlorobenzofurazan. Evaluation of ammonium 4-chloro-7-sulfobenzofurazan was undertaken using glutathione as a model thiol peptide and bovine serum albumin and jackbean urease as thiol-containing proteins. Thiol specificity of this reagent was established using various amino acids and peptides including l -cysteine, l -lysine, l -histidine, l -tyrosine, glutathione, and oxidized glutathione. Nitrogen and sulfur derivatives of ethanediol and acetic acid were also investigated. Optimum conditions for the thiol labeling reaction have been investigated using the parameters of pH, buffer type, time, temperature, and relative concentrations. Under appropriate conditions the fluorescence produced by the reaction of ammonium 4-chloro-7-sulfobenzofurazan is linearly related to thiol concentration. The fluorescence intensity of 7-sulfobenzofurazan thiol derivatives are considerably greater than the corresponding 7-nitrobenzofurazan derivatives in both aqueous and aprotic solvents, rendering this reagent highly sensitive. Our preliminary experiments with proteins labeled with ammonium 4-chloro-7-sulfobenzofurazan have shown the probe to be removable by thiolysis with excess 2-mercaptoethanol.

The interaction of pentosan polysulphate (SP54) with human neutrophil elastase and connective tissue matrix components

The binding of pentosan polysulphate (SP54) to human polymorphonuclear leucocyte elastase (PMNE) and some of its natural and synthetic substrates has been investigated. Using an ion exchange (DE52) assay system the binding of SP54 to PMNE was found to be 100 times stronger than to collagen or proteoglycan (PG). While the order for in vitro binding of the drug to purified substrates was found to be PG greater than gelatin greater than type I collagen, in vivo experiments indicated that SP54 was localized in tissues rich in collagen. Using gel-exclusion chromatography it was shown that these tissues also contained proteinaceous components other than PG and collagen which interacted with SP54. These results indicate that the potent inhibitor activity of SP54 against PMNE (50% inhibition at 1.7 X 10(-7)M) probably occurs by a specific interaction with the enzyme rather than by substrate binding inhibition, although the latter interaction may be important for localising the drug in these tissues.

Inhibition and activation of wheat embryo calcium-dependent protein kinase and inhibition of avian myosin light chain kinase by long chain aliphatic amphiphiles

Abstract Wheat embryo Ca2+-dependent protein kinase (CDPK) is inhibited by a variety of long chain amphiphilic compounds that also inhibit avian myosin light chain kinase (MLCK), namely by straight chain alkylamines, alkyltrimethylammonium halides and N- alkyl -N,N- dimethyl -3- ammonio -1- propane - sulfonates . These compounds also interact with calmodulin as assessed from enhancement of Ca2+-dependent dansyl-calmodulin fluorescence. A further common feature of these inhibitors is a greatly decreased inhibitory effectiveness at alkyl carbon chain length ≤ 12 . Long chain acylcholines with acyl carbon chain length greater than 12 inhibit wheat germ CDPK but long chain acyl carnitines are ineffective. Acylcarnitines activate CDPK in the presence and absence of Ca2+. d -Sphingosine and dihydrosphingosine inhibit both avian MLCK and plant CDPK. Sodium alkysulphates at about 10−4 M inhibit MLCK but not plant CDPK. Dihydrosphingosine and sodium alkysulphates activate wheat germ CDPK in the presence and absence of Ca2+.

A general synthesis of 2,5-diaryl-4-chloro (or bromo)oxazoles

Reaction between acyleyanides (ArCOCN) and aldehydes (ArCHO) in the presence of ether and hydrogen chloride (or hydrogen bromide) gives good yields of 2,5-diaryl-4-chloro (or bromo)oxazoles (2).

Interaction of heparin and SP54 with gelatin

Abstract Using 13C n.m.r., the interaction of heparin and SP54 with gelatin was investigated. From chemical shift and relaxation time measurements, the stoichiometry, mode of binding and association constants for the interaction were determined. The stoichiometry was found to be 2:1 (polysaccharide; gelatin), with the interaction occurring between the sulphate and carboxyl groups on the polysaccharide and the lysyl amino and arginyl guanidyl residues of gelatin. The interaction was found to be electrostatic, shown by the disruption of the complex at concentrations of sodium chloride greater than 0.5 m . The association constants of these two sulphated polysaccharides and gelatin were found to be between 104-105- m −1. It was shown that a correlation exists between microscopic association constants and relaxation times.

Effects of 4-nitro- and 4-sulpho-7-substituted benzofurazans on nucleic acid and protein synthesis of a malignant fibrosarcoma cell line in combination with mild hyperthermia

The inhibitory effects of substituted nitro- and sulphobenzofurazans on DNA, RNA and protein synthesis were compared in a new malignant fibrosarcoma cell line at 37 degrees C and 41 degrees C. The effects of these drugs with and without mild hyperthermia were evaluated by determining the % inhibition of incorporation of 3H-precursors into DNA, RNA and protein. None of the sulphobenzofurazan derivatives (Sbf) were effective inhibitors of nucleic acid and protein synthesis at 37 degrees C nor did they enhance the inhibitory effect of hyperthermia alone. The nitrobenzofurazan derivatives (Nbf) at concentrations 10% that used for the Sbf derivatives strongly inhibited biopolymer synthesis in a dose related manner; 4-chloro-7-nitrobenzofurazan (Nbf-Cl) being the most potent inhibitor. Hyperthermia amplified the effect of all the Nbf compounds tested on RNA and protein synthesis but did not further affect DNA synthesis. This selective synergistic effect was most pronounced when the lowest concentrations of Nbf compounds were studied. The synergism however, did not follow a uniform pattern. 6-Mercaptopurine and 6-(1-methyl-4-nitro-5-imidazoyl)thiopurine (Azathioprine) (100 microM) had marginal effects on nucleic acid and protein synthesis when the cells were exposed to these two thiopurines for 1 h at both 37 degrees C and 41 degrees C and they had only a moderate inhibitory effect after exposure for 15 h.