Antimicrobial agents from higher plants. Antimicrobial agents from Peganum harmala seeds

Radical reactions with 3H-quinazolin-4-ones: synthesis of deoxyvasicinone, mackinazolinone, luotonin A, rutaecarpine and tryptanthrin

Alkyl, aryl, heteroaryl and acyl radicals have been cyclised onto the 2-position of 3H-quinazolin-4-one. The side chains containing the radical precursors were attached to the nitrogen atom in the 3-position. The cyclisations take place by aromatic homolytic substitution hence retain the aromaticity of the 3H-quinazolin-4-one ring. The highest yields were obtained using hexamethylditin to facilitate cyclisation rather than reduction without cyclisation. The alkaloids deoxyvasicinone , mackinazolinone , tryptanthrin , luotonin A and rutaecarpine were synthesised by radical cyclisation onto 3H-quinazolin-4-one.

Rhodium-Catalyzed Direct C−H Addition of 3,4-Dihydroquinazolines to Alkenes and Their Use in the Total Synthesis of Vasicoline

The inter- and intramolecular couplings of unactivated alkenes to 3,4-dihydroquinazolines with a Rh(I) catalyst are reported. Coupling between olefins and NH-3,4-dihydroquinazoline was found to occur consecutively with heterocycle dehydrogenation in the presence of a Rh(I)/PCy3/HCl catalyst. The reaction was used to develop an effective method for the synthesis of 2-substituted quinazolines through an oxidative workup step. The regiocontrolled synthesis and Rh-catalyzed cyclization of alkene-tethered 3,4-dihydroquinazolines are also described. Applying this method, the second total synthesis of vasicoline was achieved. The key Rh-catalyzed cyclization step was made possible by the use of a rigid bicyclic phosphine ligand. The synthesis further demonstrates a challenging Cu-catalyzed amidation of an ortho-substituted aryl chloride.

Privileged structure-based quinazolinone natural product-templated libraries: Identification of novel tubulin polymerization inhibitors

A focused quinazolinone natural product-templated library was designed and synthesized. Compounds from this privileged structure-based library were identified as antimitotic agents acting through destabilization of tubulin polymerization. The results suggested that 2 could be a privileged substructure.

Novel One-Pot Total Syntheses of Deoxyvasicinone, Mackinazolinone, Isaindigotone, and Their Derivatives Promoted by Microwave Irradiation

[reaction: see text]. Total syntheses of deoxyvasicinone (1), mackinazolinone (2), and 8-hydroxydeoxyvasicinone (3) via novel microwave-assisted domino reactions, as well as a novel three-component one-pot total synthesis of isaindigotone (5) promoted by microwave irradiation, are reported. The efficient reaction process enabled us to rapidly access related natural product derivatives and to identify a new class of cytotoxic agents.

The in vitro antibacterial activity of Turkish medicinal plants

A total of 76 extracts from 35 plants available in the Turkish flora were assayed for their in vitro antibacterial activities against five pathogenic bacteria and a yeast. Sixteen crude extracts from eight plant species were found to possess an activity against at least one or more test microorganisms. Bioassay-guided fractionation of the most active crude extracts was also carried out with the most active extracts. Activity against Staphylococcus aureus, Bacillus cereus, Branhamella catarrhalis, Escherichia coli, Clostridium perfringens and Candida albicans (yeast) is discussed.

Phytotherapy of hypertension and diabetes in oriental Morocco

In order to select the main medicinal plants used in folk medicine to treat arterial hypertension and/or diabetes, a survey was undertaken in different areas of oriental Morocco. The patients (370 women and 256 men) were divided into three groups: diabetics (61%), hypertensives (23%) and hypertensive diabetic persons (16%). On average, 67.51% of patients regularly use medicinal plants. This proportion is perceptibly the same in all groups and does not depend on sex, age and socio-cultural level. This result shows that phytotherapy is widely adopted in northeastern Morocco. For diabetes, 41 plants were cited, of which the most used were Trigonella foenum-graecum L. (Leguminosae), Globularia alypum L. (Globulariaceae), Artemisia herba-alba Asso. (Compositae), Citrullus colocynthis (L.) Schrad. (Cucurbitaceae) and Tetraclinis articulata Benth. (Cupressaceae). In the hypertension's therapy 18 vegetal species were reported, of which the most used were Allium sativum L. (Liliaceae), Olea europea L. (Oleaceae), Arbutus unedo L. (Ericaceae), Urtica dioica L. (Urticaceae) and Petroselinum crispum A.W. Hill (Apiaceae). Among the 18 species used for hypertension, 14 were also employed for diabetes. Moreover, these two diseases were associated in 41% of hypertensives. These findings suggest that hypertension observed in this region would be in a large part related to diabetes.

Hypothermic effect of harmala alkaloid in rats: involvement of serotonergic mechanism

The effect of total alkaloid extracted from Peganum harmala seeds collected in Egypt on body temperature was studied in rats. Intraperitoneal administration of the Peganum harmala extract produced significant and dose-dependent hypothermia. Similarly, harmine and harmaline, major constituents of the harmala alkaloid, lowered the body temperature. Pretreatment with p-chlorophenylalanine (100 mg/kg/day for 3 days), a 5-HT synthesis inhibitor, significantly attenuated the hypothermic effect of the total alkaloid and harmine, while it tended to block the hypothermic action of harmaline. Methysergide (2 mg/kg), a 5-HT antagonist, significantly attenuated the hypothermia induced by harmala alkaloids. Pindolol (0.05-2 mg/kg), a 5-HT1A receptor and beta-adrenoceptor antagonist, partly blocked the hypothermic effect of the harmala alkaloids in a dose-dependent manner, whereas propranolol (10 mg/kg), a beta-adrenoceptor antagonist, failed to alter it, suggesting that beta-adrenoceptor is not involved in the hypothermia caused by the alkaloids. Pretreatment with a dopamine receptor antagonist haloperidol (5 mg/kg, s.c. and 2 mg/kg, i.p. 24 and 2 h before the experiment, respectively) significantly attenuated the hypothermic effect of harmala alkaloids. Moreover, in haloperidol pretreated rats, methysergide (2 mg/kg, i.p.) and pindolol (0.05 and 2 mg/kg) completely attenuated the hypothermic effect of the alkaloids. These data suggest that harmala alkaloids produce hypothermic effect mainly through endogenous 5-HT stimulation of 5-HT1A receptor.

Chapter 1 Allelochemical Properties or the Raison D'être of Alkaloids

This chapter provides evidence that alkaloids are not waste products or functionless molecules as formerly assumed, but rather defense compounds employed by plants for survival against herbivores and against microorganisms and competing plants. These molecules were developed during evolution through natural selection in that they fit many important molecular targets, often receptors, of cells, which are seen in molecules that mimic endogenous neurotransmitters. The chapter discusses that microorganisms and herbivores rely on plants as a food source. Since both have survived, there must be mechanisms of adaptations toward the defensive chemistry of plants. Many herbivores have evolved strategies to avoid the extremely toxic plants and prefer the less toxic ones. Many herbivores have potent mechanisms to detoxify xenobiotics, which allow the exploitation of at least the less toxic plants. In insects, many specialists evolved that are adapted to the defense chemicals of their host plant, in that they accumulate these compounds and exploit them for their own defense. Alkaloids function as defense molecules against insect predators in the examples studied, and this is further support for the hypothesis that the same compound also serves for chemical defense in the host plant. It needs more experimental data to understand fully the intricate interconnections between plants, their alkaloids, and herbivores, microorganisms, and other plants.

Synthesis and characterization of novel biologically active platinum(II) and palladium(II) complexes of some beta-carboline alkaloids

The preparation of novel biologically active platinum(II) and palladium(II) complexes of some beta-carboline alkaloids (harmaline, harmalol, harmine, and harmane) is described. These complexes, characterized on the basis of their CHN elemental analysis, infrared, Raman and 1H and 13C nuclear resonance spectral data, were shown to have the empirical formula [M(alkaloid)Cl2], M = Pt, Pd. The antitumor and antiviral activities of some of these complexes have been demonstrated.

Screening methods for natural products with antimicrobial activity: a review of the literature

Diffusion and dilution methods have been employed to study the antimicrobial activity of medicinal plants. A number of modifications have been made in the technique in order to obtain better results. Since some factors (culture medium composition, microorganisms tested, extractive method, pH, solubility of the sample in the culture medium, etc.) can change results, it is difficult using these methods to standardize a procedure for the study of antimicrobial plants. Bioautography is another method for studying antimicrobial activity. With it, previously chromatographed principles are diffused to the agar. The results can also change according to the method employed. All the various techniques are reviewed here and, in order to unify the different criteria and parameters, standard methods to study the antimicrobial activity of medicinal plants are proposed.

Screening of antimicrobial activity of some plants belonging to the Apocynaceae and Loganiaceae

A review is given of the literature on the antimicrobial activity of various indole alkaloids. The data are briefly discussed. A screening was performed of a series of plants belonging to the indole alkaloid rich plant families Apocynaceae and Loganiaceae, 25 materials representing 14 Apocynaceae species and 54 materials representing 41 Strychnos species were investigated. No activity against the yeast or the fungus, used as test organisms was found. A number of extracts showed activity against the gram-positive test organisms, 4 species showed activity against gram-negative bacteria.