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

(NH4)2S2O8 promoted tandem radical cyclization of quinazolin-4(3H)-ones with oxamic acids for the construction of fused quinazolinones under metal-free conditions

A novel cascade radical addition/cyclization reaction of non-activated olefins and oxamic acids has been proposed. Under transition metal-free conditions, 36 quinazolinone derivatives containing an amide moiety were successfully synthesized, with the highest yield being 81%. This method involves the preparation of aminoacyl fused quinazolinone derivatives under mild conditions, offering advantages such as a high yield, a broad substrate compatibility, and a high atom economy.

Persulfate-Promoted Carbamoylation/Cyclization of Alkenes: Synthesis of Amide-Containing Quinazolinones

The incorporation of amide groups into biologically active molecules has been proven to be an efficient strategy for drug design and discovery. In this study, we present a simple and practical method for the synthesis of amide-containing quinazolin-4(3H)-ones under transition-metal-free conditions. This is achieved through a carbamoyl-radical-triggered cascade cyclization of N3-alkenyl-tethered quinazolinones. Notably, the carbamoyl radical is generated in situ from the oxidative decarboxylative process of oxamic acids in the presence of (NH4)2S2O8.

Synthesis of 2,3-Fused Quinazolinones via the Radical Cascade Pathway and Reaction Mechanistic Studies by DFT Calculations

An efficient radical cascade cyclization of unactivated alkenes toward the synthesis of a series of ring-fused quinazolinones has been developed in moderate to excellent yields using commercially available ethers, alkanes, and alcohols, respectively, under a base-free condition in a short time without a transition metal as catalyst. Notably, the transformations can be carried out with the advantages of a broad substrate scope and high atomic economy. Density functional theory calculations and wavefunction analyses were performed to elucidate the radical reaction mechanism.

An Oxidant-Free and Mild Strategy for Quinazolin-4(3H)-One Synthesis via CuAAC/Ring Cleavage Reaction

An oxidant-free and highly efficient synthesis of phenolic quinazolin-4(3H)-ones was achieved by simply stirring a mixture of 2-aminobenzamides, sulfonyl azides, and terminal alkynes. The intermediate N-sulfonylketenimine underwent two nucleophilic additions and the sulfonyl group eliminated through the power of aromatization. The natural product 2-(4-hydroxybenzyl)quinazolin-4(3H)-one can be synthesized on a large scale under mild conditions with this method.

Metal-Free Photoinduced Hydrocyclization of Unactivated Alkenes toward Ring-Fused Quinazolin-4(3H)-ones via Intermolecular Hydrogen Atom Transfer

A visible-light-induced hydrocyclization of unactivated alkenes was developed using 3CzClIPN as the photocatalyst to generate substituted α-methyldeoxyvasicinones and α-methylmackinazolinones in moderate to good yields. An intermolecular hydrogen atom transfer with THF as the hydrogen source was involved. Mechanism studies indicated that the intramolecular addition of the in situ formed aminal radical to the unactivated alkene generated the polycyclic quinazolinone.

Rational drug design strategies for the development of promising multi-target directed indole hybrids as Anti-Alzheimer agents

Alzheimer's disease (AD) is a neurological disorder that leads to dementia i.e., progressive memory loss accompanied with worsening of thinking ability of an individual. The cause of AD is not fully understood but it progresses with age where brain cells gradually die over time. According to the World Health Organization (WHO), currently 50 million people worldwide are affected by dementia and 60-70% of the cases belong to AD. Cumulative research over the past few decades have shown that molecules that act at a single target possess limited efficacy since these investigational drugs are not able to act against complex pathologies and thus do not provide permanent cure. Designing of multi-target directed ligands (MTDLs) appears to be more beneficial and a rational approach to treat chronic complex diseases including neurodegenerative diseases. Recently, MTDLs are being extensively researched by the medicinal chemists for the development of drugs for the treatment of various multifactorial diseases. Indole is one of the privileged scaffolds which is considered as an essential mediator between the gut-brain axis because of its neuroprotective, anti-inflammatory, β-amyloid anti-aggregation and antioxidant activities. Herein, we have reviewed the potential of some indole-hybrids acting at multiple targets in the pathogenesis of AD. We have reviewed research articles from the year 2014-2021 from various scientific databases and highlighted the synthetic strategies, mechanisms of neuroprotection, toxicity, structure activity relationships and molecular docking studies of various indole-hybrid derivatives. This literature review of published data on indole derivatives indicated that developing indole hybrids have improved the pharmacokinetic profile with lower toxicity, provided synergistic effect, helped to develop more potent compounds and prevented drug-drug interactions. It is evident that this class of compounds have potential to inhibit multiple enzymes targets involved in the pathogenesis of AD and therefore indole hybrids as MTDLs may play an important role in the development of anti-AD molecules.

Copper-catalyzed three-component N-alkylation of quinazolinones and azoles

A Cu-catalyzed three-component N-alkylated coupling reaction of N-heteroarenes with methyl ketones and one carbon source has been developed. Using methyl ketones as alkylation reagent and DMPA (N,N’-dimethylpropionamide) as one carbon...

Cyanomethylative cyclization of unactivated alkenes with nitriles for the synthesis of cyano-containing ring-fused quinazolin-4(3H)-ones

The synthesis of cyano-containing pyrrolo- and piperidino-quinazolinones was developed using alkyl nitriles through radical cascade addition/cyclization under metal-free conditions.

Antimicrobial properties of Peganum harmala L. seeds' smoke in indoors: applications and prospects

Peganum harmala L., known as Harmal or African, Syrian Rue, Espand (in Iranian culture), and Ozallaik (in Turkey), is a perennial herbaceous glabrous plant, which offers many antimicrobial activities in indoor air. In this regard, in the present study, we aimed at evaluating the disinfectant effects of Peganum harmala L. (PHL) seed smoke on microbial load in air. For this reason, the effects of four doses of PHL seeds (5, 10, 15, and 20 g) and various sampling times in the range of 0-30 min were examined on its antibacterial and antifungal effects. The experiments were conducted at two different areas including a classroom located at the health faculty of Ahvaz University of Medical Sciences and a residential area with a similar volume of 60 m³. Tryptic soy agar (TSA) was applied as a specific bacterial culture medium, and sabouraud dextrose agar (SDA) was used as a specific fungal culture medium. The concentration of bacteria and fungi in the indoor air of the residential area decreased by 71.4 and 94.7%, respectively. In the educational area, the concentration of bacteria and fungi decreased by 92.8 and 88.9%, respectively. In conclusion, the PHL smoke showed antibacterial and antifungal effects, which may be due to its alkaloids harmine properties, while it causes an increase in the concentration of particles in the air of indoor environments. Therefore, it can be used as an indoor air disinfectant for decreasing the load of bacteria and viruses in a closed space.

Alkaloids of Peganum harmala: Anticancer Biomarkers with Promising Outcomes

BACKGROUND

Cancer is a serious and growing global health issue worldwide. In the cancerous cells, the normal cell cycle has been disrupted via a series of irreversible changes. Recently, the investigations on herbal medicine and clarifying the phytochemicals potential in treat cancer has been increased. The combination of phytochemicals with conventional cancer treatment approaches can improve outcomes via advancing cell death, restraining cell proliferation and invasion, sensitizing cancerous cells, and promoting the immune system. Therefore, phytochemicals can be introduced as relevant complementary medicaments in cancer therapy. Peganum harmala L. (Zygophyllaceae) as a valuable medicinal herb, possesses various alkaloid ingredient.

OBJECTIVE

Pointing to the importance of new avenues for cancer management and P. harmala convincing effect in this field, this review strived to collect a frame to epitome possible scopes to develop novel medicines in cancer treatment.

METHODS

Keywords "Peganum harmala" and cancer, or chemotherapy, or anti-neoplasm were searched through the "Scopus" database up to 29th of February 2020. Papers linking to agriculture, chemistry, environmental, and genetics sciences were omitted and, papers centered on cancer were selected.

RESULTS AND DISCUSSION

In the current study, 42 related papers to cancer treatment and 22 papers on alkaloid bioactive components are collected from 72 papers. The β-carboline alkaloids derived from P. harmala, especially harmine, demonstrate notable anticancer properties by targeting apoptosis, autophagy, abnormal cell proliferation, angiogenesis, metastasis, and cytotoxicity. Based on the collected information, P. harmala holds significant anticancer activity. Considering the mechanism of the various anticancer drugs and their acting similarity to P. harmala, the alkaloids derived from this herb, particularly harmine, can introduce as a novel anticancer medicine solely or in adjuvant cancer therapy.

Self-Catalyzed Phototandem Perfluoroalkylation/Cyclization of Unactivated Alkenes: Synthesis of Perfluoroalkyl-Substituted Quinazolinones

A novel visible-light-induced radical tandem trifluoromethylation/cyclization of unactivated alkenes with sodium perfluoroalkanesulfinates (R_f = CF₃, C₃F₇, C₄F₉, C₆F₁₃, C₈F₁₇) under air atmosphere has been developed. A range of quinazolinones containing unactivated alkene moiety and sodium perfluoroalkanesulfinates were compatible with this transformation, leading to a variety of perfluoroalkyl-substituted quinazoline alkaloids. Remarkably, the experiment can be carried out without any metal catalyst, strong oxidant, or external photosensitizer.

Alkaloids isolated from Tabernaemontana bufalina display xanthine oxidase inhibitory activity

Continued interest in bioactive alkaloids led to the isolation of four undescribed alkaloids along with 74 known ones from the aerial parts of Tabernaemontana bufalina Lour. The structures of the yet undescribed alkaloids were elucidated based on NMR, IR, UV, MS and CD spectroscopic data and X-ray crystal diffraction and, according to the plant source, named as taberhaines A-D (1-4). The known compounds comprised of 66 monoterpenoid indole, three carboline and five isoquinoline alkaloids. Among them, the known apparicine inhibited significantly the activity of xanthine oxidase, which plays an important role for gout, with an IC₅₀ value of 0.65 μM, compared to the standard drug allopurinol (IC₅₀ = 0.60 μM).

Synthesis of 1,2-Dihydroquinazolines via Rearrangement of Indazolium Salts

A convenient synthesis of 1,2-dihydroquinazolines via rearrangement of indazolium salts was described. A mechanistic study using isotope labeling experiment revealed that the rearrangement passes through cleavage of N-N bond/ring opening after basic deprotonation of 2-benzyl in indazolium salts to yield intermediate E, which proceeds in an intramolecular N-nucleophilic addition to form the observed product. Computational analyses imply that the pathway of the rearrangement is determined by the energy barriers of the ring-closing process and the stability of the product.

Discovery of a tetrazolyl β-carboline with in vitro and in vivo osteoprotective activity under estrogen-deficient conditions

β-Carbolines have been assessed for osteoclastogenesis. However, their effect on osteoblasts during estrogen deficiency is still unclear. Here, a series of novel piperazine and tetrazole tag β-carbolines have been synthesized and examined for osteoblast differentiation in vitro. In vitro data suggest that compound 8g is the most promising osteoblast differentiating agent that was evaluated for in vivo studies. Compound 8g promoted osteoblast mineralization, stimulated Runx2, BMP-2 and OCN expression levels, increased BrdU incorporation and inhibited generation of free radicals as well as nitric oxide. Since a piperazine group is involved in bone repair activity and β-carboline in IκB kinase (IKK) inhibition, compound 8g inhibited tumor necrosis factor α (TNFα) directed IκBα phosphorylation, preventing nuclear translocation of NF-κB thereby alleviating osteoblast apoptosis. In vivo studies show that compound 8g was able to restore estrogen deficiency-induced bone loss in ovariectomized rats without any toxicity, thus signifying its potential in bone-protection chemotherapy under postmenopausal conditions.

Design, synthesis and evaluation of novel bivalent β-carboline derivatives as multifunctional agents for the treatment of Alzheimer's disease

To develop potent multi-target ligands against Alzheimer's disease (AD), a series of novel bivalent β-carboline derivatives were designed, synthesized, and evaluated. In vitro studies revealed these compounds exhibited good multifunctional activities. In particular, compounds 8f and 8g showed the good selectivity potency on BuChE inhibition (IC₅₀ = 1.7 and 2.7 μM, respectively), Aβ_1-42 disaggregation and neuroprotection. Compared with the positive control resveratrol, 8f and 8g showed better activity in inhibiting Aβ_1-42 aggregation, with inhibitory rate 82.7% and 85.7% at 25 μM, respectively. Moreover, compounds 8e, 8f and 8g displayed excellent neuroprotective activity by ameliorating the impairment induced by H₂O₂, okadaic acid (OA) and Aβ_1-42 without cytotoxicity in SH-SY5Y cells. Thus, the present study evidently showed that compounds 8f and 8g are potent multi-functional agents against AD and might serve as promising lead candidates for further development.

Reductive cyclisations of amidines involving aminal radicals

The first general study of aminal radical cyclisations, triggered by reduction of amidines with SmI₂, delivers quinazolinones with complete diastereocontrol.

Total synthesis of natural productsviairidium catalysis

An overview of the highlights in total synthesis of natural products using iridium as a catalyst is given.

Synthesis and in-vitro anti-leishmanial activity of (4-arylpiperazin-1-yl)(1-(thiophen-2-yl)-9H-pyrido[3,4-b]indol-3-yl)methanone derivatives

In the present study, we have reported synthesis and biological evaluation of a series of fifteen 1-(thiophen-2-yl)-9H-pyrido[3,4-b]indole derivatives against both promastigotes and amastigotes of Leishmania parasites responsible for visceral (L. donovani) and cutaneous (L. amazonensis) leishmaniasis. Among these reported analogues, compounds 7b, 7c, 7f, 7g, 7i, 7j, 7m, 7o displayed potent activity (15.55, 7.70, 7.00, 3.80, 14.10, 9.25, 3.10, 4.85μM, respectively) against L. donovani promastigotes than standard drugs miltefosine (15.70μM) and pentamidine (32.70μM) with good selectivity index. In further, in-vitro evaluation against amastigote forms, two compounds 7g (8.80μM) and 7i (7.50μM) showed significant inhibition of L. donovani amastigotes. Standard drug amphotericin B is also used as control to compare inhibition potency of compounds against both promastigote (0.24μM) and amastigote (0.05μM) forms.

Cytotoxic Constituents and Mechanism from Peganum harmala

Peganum harmala L. is a traditional Chinese and Uygur medicine used to treat cancer. Bioactivity-guided fractionation was applied to determine the cytotoxic constituents from P. harmala. A novel triterpenoid and a phenolic glycoside were isolated and identified, as well as seven known compounds. The novel metabolites were elucidated to be 3α-acetoxy-27-hydroxyolean-12-en-28-oic acid methyl ester (1, OA) and N-acetyl-9-syringinoside (9). Some compounds exhibited potent cytotoxicity against human tumor cells. Among them, OA showed the highest cytotoxicity against human lung cancer cells A549 with an IC50 value of 8.03 ± 0.81 μm. OA had a potent anti-NSCLC cell activity by interfering with the epidermal growth factor receptor (EGFR) activation and its downstream signaling, and could exert an antiproliferative effect by inactivation of EGFR-driven antiapoptotic pathway followed by the release of mitochondrial cytochrome c, which might prove to be a promising leading compound for the development of an anti-lung cancer drug.

Exploring nuruk aroma; Identification of volatile compounds in commercial fermentation starters

Volatile compounds of 7 commercial fermentation starters, including 4 traditional nuruk, 2 ipguk, and 1 crude amylolytic enzyme, were extracted using solvent-assisted flavor evaporation (SAFE), and extracts were analyzed using GC-MS. A total of 70 volatile compounds, including 4 esters, 10 acids, 16 alcohols, 16 hydrocarbons, 9 ketones, 5 aldehydes, 3 volatiles phenols, and 7 miscellaneous components were identified. Concentrations of volatile compounds, including 4,6-dimethylundecane, methyl 2-hydroxybenzoate, 1-hexanol, 2-phenylethanol, 3-methylbutanoic acid, and hexanoic acid were higher in 4 traditional nuruk starters than in others. The major volatile components in 2 ipguk starters were the hydrocarbones dodecane, heptadecane, octadecane, and nonadecane. Concentrations of 2-methoxy-4-vinylphenol and 3-hydroxy-2-butanone were highest in the crude amylolytic enzyme starter. Compositions and amounts of volatile compounds were different among the 7 commercial fermentation starters.

Cytotoxic indole alkaloids against human leukemia cell lines from the toxic plant Peganum harmala

Bioactivity-guided fractionation was used to determine the cytotoxic alkaloids from the toxic plant Peganum harmala. Two novel indole alkaloids, together with ten known ones, were isolated and identified. The novel alkaloids were elucidated to be 2-(indol-3-yl)ethyl-α-L-rhamnopyranosyl-(1 → 6)-β-D-glucopyranoside (2) and 3-hydroxy-3-(N-acetyl-2-aminoethyl)-6-methoxyindol-2-one (3). The cytotoxicity against human leukemia cells was assayed for the alkaloids and some of them showed potent activity. Harmalacidine (compound 8, HMC) exhibited the highest cytotoxicity against U-937 cells with IC50 value of 3.1 ± 0.2 μmol/L. The cytotoxic mechanism of HMC was targeting the mitochondrial and protein tyrosine kinase signaling pathways (PTKs-Ras/Raf/ERK). The results strongly demonstrated that the alkaloids from Peganum harmala could be a promising candidate for the therapy of leukemia.

Antitumor quinazoline alkaloids from the seeds of Peganum harmala

A phytochemical study on the methanol extracts from the seeds of Peganum harmala L. led to a new quizonaline alkaloid (S)-vasicinone-1-O-β-d-glucopyranoside (1) and four known ones, (R)-vasicinone-1-O-β-d-glucopyranoside (2), (S)-vasicinone (3), vasicine (4), and deoxyvasicinone (5). Their structures were elucidated by spectroscopic analysis including IR, HR-ESI-MS, 1D and 2D NMR, and specific rotation as well as by comparison of the data with those in the literature. All of the alkaloids were screened for antiproliferative activity against human gastric cancer cells MCG-803 with MTT method. Compounds 1 and 3 exhibited moderate inhibitory activity.

Direct access to pyrido/pyrrolo[2,1-b]quinazolin-9(1H)-ones through silver-mediated intramolecular alkyne hydroamination reactions

We report a synthetic methodology for the construction of the fused heterocyclic compounds pyrido[2,1-b]quinazolin-9(1H)-ones and pyrrolo[2,1-b]quinazolin-9(1H)-ones through an AgOTf-catalyzed intramolecular alkyne hydroamination reaction. The methodology is applicable to a wide scope of substrates and produces a series of fused quinazolinone heterocycles in good to excellent yields.

Discovery of deoxyvasicinone derivatives as inhibitors of NEDD8-activating enzyme

NEDD8-activating enzyme (NAE) controls the specific degradation of proteins regulated by cullin-RING ubiquitin E3 ligases, and has been considered as an attractive molecular target for the development of drugs against cancer. A pharmacophore model constructed from a training set of deoxyvasicinone derivatives was used to screen 376 compounds from an analogue database. From the initial screening, the valine-linked deoxyvasicinone derivative 9 and the N-isopropyl-linked deoxyvasicinone derivative 10 emerged as the top scoring candidates. Compounds 9 and 10 showed micromolar potencies in both cell-free and cell-based systems, with selectivity for NAE over the related enzymes SAE and UAE. Molecular modelling analysis suggested that 9 and 10 may inhibit NAE by blocking the ATP-binding domain. Thus, these deoxyvasicinone derivatives could be considered as promising lead molecules for the development of more potent inhibitors of NAE.

Characterization of markers of botanical origin and other compounds extracted from unifloral honeys

The possibility of tracing the botanical and geographical origin of products such as honey has become more important because of market globalization. As a consequence, numerous analytical methods have been applied to the determination of honey authenticity. The scope of the present work is to chromatographically purify and characterize 23 compounds from organic extracts of unifloral (chestnut, linden, orange, acacia, eucalyptus, honeydew) and polyfloral honeys. Of these compounds, 17 were identified as specific markers and were used for botanical discrimination in a previous study based on multivariate statistical analysis of proton nuclear magnetic resonance ((1)H NMR) data. Together with the botanical markers, 6 other substances were isolated and characterized using NMR and mass spectrometry. These phytochemicals belong to several classes, that is, terpenes, organic acids, flavonoids, and others. For the first time, a diacylglyceryl ether and 5 other compounds present in different types of honey were identified and characterized.

Discovery of a natural product inhibitor targeting protein neddylation by structure-based virtual screening

NEDD8-activating enzyme (NAE) controls the specific degradation of proteins regulated by cullin-RING ubiquitin E3 ligase, and has been considered as an attractive molecular target for the development of anti-cancer drugs. We report herein the identification of the dipeptide-conjugated deoxyvasicinone derivative (1) as an inhibitor of NAE by virtual screening of over 90,000 compounds from the ZINC database of natural products. Molecular modelling results suggested that 1 may be a non-covalent competitive inhibitor of NAE by blocking the ATP-binding domain. Compound 1 was able to inhibit NAE activity in both cell-free and cell-based assay with potencies in the micromolar range and selectivity over analogous E1 enzymes UAE and SAE. We envisage that the identification and molecular docking analysis of this bioactive scaffold as an NAE inhibitor would provide the scientific community with useful information in order to generate more potent analogues.

An ethnoveterinary study of medicinal plants in treatment of diseases and syndromes of herd dog in southern regions of Ilam province, Iran

This paper describes a selection of the ethnoveterinary medicines used for herd dogs in the southern regions of Ilam province, Iran. Traditional botanical medicine is the primary mode of healthcare for most of the rural population in Ilam province. In this study, a questionnaire was distributed among 45 residential areas in 22 rural zones of the southern areas of Ilam province. The objective of this study was the recognition of natural medicinal methods using medicinal plants, and the classification of ethnoveterinary applications and collection of domestic science. Twenty-two medicinal plants from 16 families were identified. The main application of these plants was for the detection and treatment of digestive disorders using Citrullus colocynthis, Aristolochia clematis, Scrophularia deserti, Quercus brantii, Ceracus microcarpa, Echium strigosa, Pistacia atlantica, and Pistacia khinjuk which have been applied using Euphurbia graminifolius, Peganum harmala, Salsola rigida, Artemisia herba-alba, Amygdalus arabica, jolbak of salt water, Peganum harmala L., and Nicotina tabacum for external and internal parasite disorders. S. deserti for ophthalmic disorders, and P. atlantica, P. khinjuk, and Q. brantii for respiratory disorders were applied. The present study confirmed the traditional medical effects of some plants and revealed the unique medical effects of other plants, which if recognized could be useful in the creation of new ideas and increasing knowledge for the modern pharmaceutical industry. Since very few clinical trials have been conducted on plants native to Ilam province, it is necessary that more research be conducted to ensure that labeled and standardized products are introduced for human consumption.

(4-Nitrophenyl)(1,2,3,9-tetrahydropyrrolo[2,1-b]quinazolin-3-yl)methanol monohydrate

In the crystal structure of the title compound, C₁₈H₁₇N₃O₃·H₂O, the mol­ecules are linked by O—H⋯O and O—H⋯N hydrogen bonds, resulting in a chain along the a axis. The crystal structure is stabilized by weak inter­molecular C—H⋯π (ring) hydrogen bonds and aromatic π⋯π stacking inter­actions [centroid–centroid distance = 3.902 (1) Å] between the pyrimidino rings of the quinazoline system. The tricyclic quinazoline fragment is almost planar (rms deviation = 0.0139 Å) with the two methylene C atoms of the pyrrolo ring deviating by 0.148 (2) and −0.081 (3) Å from the plane through the other atoms. The 4-nitrophenyl ring makes a dihedral angle of 12.55 (7)° with the tricyclic ring system.

(E)-3-[4-(Dimethyl-amino)-benzyl-idene]-2,3-di-hydro-1H,9H-pyrrolo-[2,1-b]quinazolin-9-one

The title compound, C(20)H(19)N(3)O, was obtained by condensation of 2,3-dihydro-1H,9H-pyrrolo-[2,1-b]quinazolin-9-one (alkaloid de-oxy-vasicinone, isolated from Peganum Harmala) with 4-(dimethyl-amino)-benzaldehyde in the presence of sodium methoxide. The 2,3-dihydro-1H,9H-pyrrolo-[2,1-b]quinazolin-9-one part of the mol-ecule is roughly planar (r.m.s. deviation = 0.0178 Å) and is essentially coplanar with the benzil-idene ring (r.m.s. deviation = 0.0080 Å), forming a dihedral angle of 5.0 (1)°. The crystal structure is stabilized by two aromatic π-π stacking inter-actions observed between the benzene rings of neighboring mol-ecules [centroid-centroid distance = 3.7555 (19) Å.

Antibacterial and antifungal activities of (beta)-carboline alkaloids of Peganum harmala (L) seeds and their combination effects

The β-carboline alkaloids of Peganum harmala L were extracted through a bioassay-guided fractionation and their antimicrobial activities were investigated. Results revealed significant differences (P>0.05) between compounds depending on the microorganism tested and the application method. When examined individually, harmine was the most effective against Proteus vulgaris, Bacillus subtilis and Candida albicans where inhibition zones ranged between 21.2 and 24.7 mm. Potentiality of the alkaloids was increased when applied as binary mixtures suggesting a kind of synergistic interaction with inhibition zones reaching 31.5mm with the total alkaloidal extract. We recommended the use of such compounds as new antimicrobial biorationals.