Manzamine alkaloids as antileishmanial agents: A review

Diverse pharmacological activities of β-carbolines: Substitution patterns, SARs and mechanisms of action

β-Carbolines, a class of indole-containing heterocyclic alkaloids, are widely distributed in nature and possess diverse bioactivities, making them promising drug candidates against a wide range of diseases. The remarkable medicinal potential of β-carbolines has spurred the pharmaceutical research community to study their derivatives extensively. This review updates the development of β-carboline derivatives in recent years (2015-2024), particularly with a focus on their anticancer, antiparasitic, antimicrobial, antiviral, and neuroprotective properties, based on the modification approaches such as substitution on indole N (ring B), pyridine or its reduced forms (ring C), and dimerization of β-carbolines. Moreover, the mechanisms of action and structure-activity relationships of these β-carboline derivatives are highlighted to offer valuable insights on the design and development of new β-carbolines with better pharmacological activities.

Azine Dearomatization in Natural Product Total Synthesis

Since antiquity, alkaloid natural products have served as medicinal ingredients that still contribute as an inspiration for the development of novel therapeutics. For the synthetic chemist, much of the importance of natural products lies in their acting as a forcing-function for the invention of new synthetic strategies and tactics for molecular assembly. With this rich history in mind, it remains an important goal for chemists to build nitrogenous structures with greater efficiency, abiding by economies of synthesis. Nitrogenous aromatic feedstocks have been an intriguing starting point for the functionalization and construction of alkaloids for several decades, but recent advances in reaction design have opened new doors for leveraging their abundance in concise synthesis. Herein, advances in this area of synthetic ingenuity will be summarized with the aim of instructing chemists towards considering dearomatization as a strategic avenue for both target-oriented and diversity-oriented synthetic campaigns. Overall, syntheses are evaluated, compared, and contrasted to give a systematic overview of this continued area of research.

Highly Enantioselective Construction of Chiral Eight-Membered Cyclic Ethers through Tandem Cyclization of Ynones and Dicarbonyl Compounds

The enantioselective synthesis of eight-membered cyclic ether has always been a challenge in organic synthesis. Herein, we reported a highly enantioselective tandem cyclization reaction of alkyne ketone and dioxypyridines mediated by chiral bifunctional catalysts. This reaction generates two adjacent stereocenters using an atomeconomic manner, providing a simple and effective method for the one-step synthesis of highly enantioselective eight-membered cyclic ethers.

Evaluation of the in vivo acute toxicity and in vitro genotoxicity and mutagenicity of synthetic β-carboline alkaloids with selective cytotoxic activity against ovarian and breast cancer cell lines

The aim of this study was to evaluate the in vitro cytotoxic, genotoxic, and mutagenic potential and to determine the in silico ADME parameters of two synthetic β-carboline alkaloids developed as prototypes of antitumor agents (NQBio-06 and NQBio-21). Additionally, acute toxicity of the compounds was evaluated in mice. The results from the MTT assay showed that NQBio-06 presented higher cytotoxicity in the ovarian cancer cell line TOV-21 G (IC50 = 2.5 µM, selectivity index = 23.7). NQBio-21 presented an IC50 of 6.9 µM and a selectivity index of 14.5 against MDA-MB-231 breast cancer cells. Comet assay results showed that NQBio-06 did not induce chromosomal breaks in vitro, but NQBio-21 was genotoxic with and without metabolic activation (S9 fraction). Micronucleus assay showed that both compounds were mutagenic. In addition, metabolic activation enhanced this effect in vitro. The in silico predictions showed that the compounds met the criteria set by Lipinski's rules, had strong prediction for intestinal absorption, and were possible substrates for P-glycoprotein. The in vivo results demonstrated that both the compounds exhibited low acute toxicity. These results suggest that the mechanisms underlying the cytotoxicity of NQBio-06 and NQBio-21 are related to DNA damage induction and that the use of S9 enhanced these effects. In vivo analysis showed signs of toxicity after a single administration of the compounds in mice. These findings highlight the potential of β-carboline compounds as sources for the development of new anticancer chemotherapeutic agents.

Recent advances in [4 + 4] annulation of conjugated heterodienes with 1,4-dipolar species for the synthesis of eight-membered heterocycles

Numerous eight-membered heterocycles are of significance in biological chemistry, the pharmaceutical industry, agrochemistry, and materials science. However, the assembly of eight-membered heterocycles is usually challenging due to the unfavorable enthalpic and entropic barriers of the transition states during the ring formation. Tremendous efforts have been devoted to the development of synthetic routes to eight-membered heterocycles. Despite these developments, the exploration of more strategies for the facile and effective assembly of eight-membered heterocyclic molecules in a single vessel under mild conditions is still highly desirable. The conjugated heterodiene-participating [4 + 4] annulation serves as a convenient and robust strategy for the synthesis of eight-membered heterocycles from easily accessible starting materials. In recent years, great progress has been achieved in this attractive field. In this short review, we highlighted the recent advances in the synthesis of eight-membered heterocycles via cascade reactions based on [4 + 4] annulation of conjugated heterodienes with 1,4-dipolar species. The brief backgrounds, the general reactions, the proposed mechanisms and their features are summarized. The prospects and challenges of this field are also outlined at the end of this review. In addition, to highlight the importance and practicality of these reactions, the properties of several series of eight-membered heterocycles have also been introduced briefly.

Metabolites and Bioactivity of the Marine Xestospongia Sponges (Porifera, Demospongiae, Haplosclerida) of Southeast Asian Waters

Sponges are aquatic, spineless organisms that belong to the phylum Porifera. They come in three primary classes: Hexactinellidae, Demospongiae, and Calcarea. The Demospongiae class is the most dominant, making up over 90% of sponge species. One of the most widely studied genera within the Demospongiae class is Xestospongia, which is found across Southeast Asian waters. This genus is of particular interest due to the production of numerous primary and secondary metabolites with a wide range of biological potentials. In the current review, the antioxidant, anticancer, anti-inflammatory, antibacterial, antiviral, antiparasitic, and cytotoxic properties of metabolites from several varieties of Southeast Asian Xestospongia spp. were discussed. A total of 40 metabolites of various natures, including alkaloids, fatty acids, steroids, and quinones, were highlighted in X. bergquistia, X. testudinaria, X. muta, X. exigua, X. ashmorica and X. vansoesti. The review aimed to display the bioactivity of Xestospongia metabolites and their potential for use in the pharmaceutical sector. Further research is needed to fully understand their bioactivities.

Marine organisms as potential sources of natural products for the prevention and treatment of malaria

Vector-borne diseases (VBDs) are a worldwide critical concern accounting for 17% of the estimated global burden of all infectious diseases in 2020. Despite the various medicines available for the management, the deadliest VBD malaria, caused by Plasmodium sp., has resulted in hundreds of thousands of deaths in sub-Saharan Africa only. This finding may be explained by the progressive loss of antimalarial medication efficacy, inherent toxicity, the rise of drug resistance, or a lack of treatment adherence. As a result, new drug discoveries from uncommon sources are desperately needed, especially against multi-drug resistant strains. Marine organisms have been investigated, including sponges, soft corals, algae, and cyanobacteria. They have been shown to produce many bioactive compounds that potentially affect the causative organism at different stages of its life cycle, including the chloroquine (CQ)-resistant strains of P. falciparum. These compounds also showed diverse chemical structures belonging to various phytochemical classes, including alkaloids, terpenoids, polyketides, macrolides, and others. The current article presents a comprehensive review of marine-derived natural products with antimalarial activity as potential candidates for targeting different stages and species of Plasmodium in both in vitro and in vivo and in comparison with the commercially available and terrestrial plant-derived products, i.e., quinine and artemisinin.

Design, synthesis and evaluation of novel β-carboline ester analogues as potential anti-leishmanial agents

Leishmaniasis is one of today's most neglected diseases. The emergence of new anti-leishmanial therapies emphasizes several study groups funded by the World Health Organization. The present investigation will focus on the research to determine a few new potential derivatives of β-carboline ester derivatives against leishmaniasis. The in-silico predicted ADMET properties of most of the titled compounds are in an acceptable range and having drug like properties. Among all the tested analogs, compound ES-3 (EC₅₀ 3.36 μM; SI > 29.80) showed comparable and equipotent anti-leishmanial activity as that of standard drug miltefosine (EC₅₀ 4.80 μM; SI > 20.80) against amastigote forms of the tested L. infantum strain. Two compounds ES-6 and ES-10 exhibited significant activity with EC₅₀ 10.16, 13.56 μM; SI > 4.90, 7.37, respectively. In-silico based molecular docking and dynamics study of the significantly active analog also performed to study the putative binding mode, interaction pattern at the active site of the target leishmanial trypanothione reductase enzyme as well as stability of the target-ligand complex. The changes in the conformation of molecules during MD (frame wise trajectory analysis) provided new insights for the development of novel potent molecules. These findings will further give insight that will help modify the compound ES-3 for better potency and the design of novel inhibitors for leishmaniasis.Communicated by Ramaswamy H. Sarma.

The Natural Alkaloid Tryptanthrin Induces Apoptosis-like Death in Leishmania spp

Leishmaniasis is a vector-borne disease against which there are no approved vaccines, and the treatment is based on highly toxic drugs. The alkaloids consist of a chemical class of natural nitrogen-containing substances with a long history of antileishmanial activity. The present study aimed at determining the antileishmanial activity and in silico pharmacokinetic and toxicological potentials of tryptanthrin alkaloid. The anti-Leishmania amazonensis and anti-L. infantum assays were performed against both promastigotes and intracellular amastigotes. Cellular viability was determined by parasites’ ability to grow (promastigotes) or differentiate (amastigotes) after incubation with tryptanthrin. The mechanisms of action were explored by mitochondrion dysfunction and apoptosis-like death evaluation. For the computational pharmacokinetics and toxicological analysis (ADMET), tryptanthrin was submitted to the PreADMET webserver. The alkaloid displayed anti-promastigote activity against L. amazonensis and L. infantum (IC₅₀ = 11 and 8.0 μM, respectively). Tryptanthrin was active against intracellular amastigotes with IC₅₀ values of 75 and 115 μM, respectively. Mitochondrial membrane depolarization was observed in tryptanthrin-treated promastigotes. In addition, parasites undergoing apoptosis-like death were detected after 18 h of exposure. In silico ADMET predictions revealed that tryptanthrin has pharmacokinetic and toxicological properties similar to miltefosine. The results presented herein demonstrate that tryptanthrin is an interesting drug candidate against leishmaniasis.

Structure-Activity Relationship of Cytotoxic Natural Products from Indonesian Marine Sponges

Indonesian marine natural products have been one of the most promising sources in the race to obtain potential drugs for cancer treatment. One of the primary producers of cytotoxic compounds is sponges. However, there are still limited sources of comprehensive reviews related to the relationship between the structure of isolated compounds and their cytotoxic activity. This review remarks the attempt to provide a preliminary guidance from the perspective of structure-activity relationship and its participation on marine natural products research. This guidance is segregated by the compound's classes and their cytotoxic targets to obtain and organized a reliable summary of inter-study of the isolated compounds and their cytotoxicity. Structure-activity relationship is well-known for its ability to tune the bioactivity of a specific compound, especially on synthetic organic chemistry and in silico study but rarely used on natural product chemistry. The present review is intended to narrow down the endless possibilities of cytotoxicity by giving a predictable structure-activity relationship for active compounds. In addition, bioactive framework leads were selected by uncovering a noticeable structure-activity relationship with the intervention of cytotoxic agents from natural sources, especially Indonesian marine sponge.

Graphical abstract

Marine alkaloids as bioactive agents against protozoal neglected tropical diseases and malaria

Covering: 2000 up to 2021Natural products are an important resource in drug discovery, directly or indirectly delivering numerous small molecules for potential development as human medicines. Among the many classes of natural products, alkaloids have a rich history of therapeutic applications. The extensive chemodiversity of alkaloids found in the marine environment has attracted considerable attention for such uses, while the scarcity of these natural materials has stimulated efforts towards their total synthesis. This review focuses on the biological activity of marine alkaloids (covering 2000 to up to 2021) towards Neglected Tropical Diseases (NTDs) caused by protozoan parasites, and malaria. Chemotherapy represents the only form of treatment for Chagas disease, human African trypanosomiasis, leishmaniasis and malaria, but there is currently a restricted arsenal of drugs, which often elicit severe adverse effects, show variable efficacy or resistance, or are costly. Natural product scaffolds have re-emerged as a focus of academic drug discovery programmes, offering a different resource to discover new chemical entities with new modes of action. In this review, the potential of a range of marine alkaloids is analyzed, accompanied by coverage of synthetic efforts that enable further studies of key antiprotozoal natural product scaffolds.

Isolation and biological activity of azocine and azocane alkaloids

Thousands of known alkaloids contain a nitrogen (N) heterocycle. While five-, six- and seven-membered N-heterocycles (ie: pyrroles, imidazoles, indoles, pyridines and azepines and their saturated variants) are common, those with an eight-membered N-heterocycle are comparatively rare. This review discusses the structure and bioactivity of alkaloids that contain an azocine (or saturated azocane) ring, and the array of sources whence they originate.

Some Scaffolds as Anti-leishmanial Agents: An Review

Leishmaniasis is a parasitic infectious neglected tropical disease transmitted to humans by the parasites of Leishmania species. Mainly three types of leishmaniasis cases such as visceral (VL), cutaneous (CL) and mucocutaneous leishmaniasis are usually observed. In many western countries, almost 700,000 to 1million peoples are suffering from leishmaniasis and it is estimated that around 26000 to 65000 deaths occurs annually. For its treatment few drugs are available however none of them are ideal to treat leishmaniasis due to long treatment, discomfort mode of administration, risk of high level toxicity, high resistance against etc. Hence so many patients are unable to take complete treatment due to the high drug resistance. The present review will focus on antileishmanial activity of reported derivatives of betacarboline, chalcone, azole, quinoline, quinazoline, benzimidazole, benzadiazapine, thiaazoles, semicarbazone and hydontoin analogues. We believe that this present study will helpful to researcher to design new antileishmanial agents.

A predictive model for additions to N-alkyl pyridiniums

Disclosed in this communication is a thorough study on the dearomative addition of organomagnesium nucleophiles to N-alkyl pyridinium electrophiles. The regiochemical outcomes have observable and predictable trends associated with the substituent patterns on the pyridinium electrophile. Often, the substituent effects can be either additive, giving high selectivities, or ablative, giving competing outcomes. Additionally, the nature of the organometallic nucleophilic component was also investigated for its role in the regioselective outcome. The effects of either reactive component are important to both the overall reactivity and site of nucleophilic addition. The utility of these observed trends is demonstrated in a concise, dearomative synthesis of a tricyclic compound shown to have insecticidal activity.

Biologically active isoquinoline alkaloids covering 2014-2018

Isoquinoline alkaloids, an important class of N-based heterocyclic compounds, have attracted considerable attention from researchers worldwide since the early 19th century. Over the past 200 years, many compounds from this class were isolated, and most of them and their analogs possess various bioactivities. In this review, we survey the updated literature on bioactive alkaloids and highlight research achievements of this alkaloid class during the period of 2014-2018. We reviewed over 400 molecules with a broad range of bioactivities, including antitumor, antidiabetic and its complications, antibacterial, antifungal, antiviral, antiparasitic, insecticidal, anti-inflammatory, antioxidant, neuroprotective, and other activities. This review should provide new indications or directions for the discovery of new and better drugs from the original naturally occurring isoquinoline alkaloids.

Recent evolution on synthesis strategies and anti-leishmanial activity of β-carboline derivatives - An update

Leishmaniasis is the most widespread pathogenic disease in several countries. Currently, no effective vaccines are available, and the control of Leishmaniasis primarily relies on decade-old chemotherapy. The treatment for the Leishmaniasis is not up to the mark. Current therapy for Leishmaniasis is ancient and requires hospitalization for the administration. These medications are also highly toxic and resistant. β-carboline, a natural indole containing alkaloid, holds a vital position in the field of medicinal chemistry with a diversified pharmacological action. The current review focuses mainly on the anti-leishmanial effects of β-carboline analogs and their synthetic strategies, structural activity relationship studies (SAR). The past ten years alterations unveiled by β-carboline analogs present in phytoconstituents and various derivatives of synthesized analogs with the mechanism of action were briefly shortlisted and illustrated.

Screening Marine Natural Products for New Drug Leads against Trypanosomatids and Malaria

Neglected Tropical Diseases (NTD) represent a serious threat to humans, especially for those living in poor or developing countries. Almost one-sixth of the world population is at risk of suffering from these diseases and many thousands die because of NTDs, to which we should add the sanitary, labor and social issues that hinder the economic development of these countries. Protozoan-borne diseases are responsible for more than one million deaths every year. Visceral leishmaniasis, Chagas disease or sleeping sickness are among the most lethal NTDs. Despite not being considered an NTD by the World Health Organization (WHO), malaria must be added to this sinister group. Malaria, caused by the apicomplexan parasite Plasmodium falciparum, is responsible for thousands of deaths each year. The treatment of this disease has been losing effectiveness year after year. Many of the medicines currently in use are obsolete due to their gradual loss of efficacy, their intrinsic toxicity and the emergence of drug resistance or a lack of adherence to treatment. Therefore, there is an urgent and global need for new drugs. Despite this, the scant interest shown by most of the stakeholders involved in the pharmaceutical industry makes our present therapeutic arsenal scarce, and until recently, the search for new drugs has not been seriously addressed. The sources of new drugs for these and other pathologies include natural products, synthetic molecules or repurposing drugs. The most frequent sources of natural products are microorganisms, e.g., bacteria, fungi, yeasts, algae and plants, which are able to synthesize many drugs that are currently in use (e.g. antimicrobials, antitumor, immunosuppressants, etc.). The marine environment is another well-established source of bioactive natural products, with recent applications against parasites, bacteria and other pathogens which affect humans and animals. Drug discovery techniques have rapidly advanced since the beginning of the millennium. The combination of novel techniques that include the genetic modification of pathogens, bioimaging and robotics has given rise to the standardization of High-Performance Screening platforms in the discovery of drugs. These advancements have accelerated the discovery of new chemical entities with antiparasitic effects. This review presents critical updates regarding the use of High-Throughput Screening (HTS) in the discovery of drugs for NTDs transmitted by protozoa, including malaria, and its application in the discovery of new drugs of marine origin.

Recent progress on the total syntheses of macrocyclic diamine alkaloids

This review highlights the progress and challenges in the chemical synthesis of macrocyclic diamine alkaloids since 2006.

Biological evaluation and structure activity relationship of 9-methyl-1-phenyl-9H-pyrido[3,4-b]indole derivatives as anti-leishmanial agents

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New anti-leishmanial agents designed through molecular hybridization approach.

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7d showed potent anti-leishmanial activity against both L. infantum & L. donovani.

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7d EC₅₀ against L. infantum promastigotes, axenic amastigotes 1.59 & 1.4 µM.

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7d EC₅₀ against L. donovani promastigotes, axenic & intracellular amastigotes 0.91 & 0.91 & 1.4 µM.

A series of piperazinyl-β-carboline-3-carboxamide derivatives were designed through a molecular hybridization approach. Designed analogues were synthesized, characterized and evaluated for anti-leishmanial activity against Leishmania infantum and Leishmania donovani. In L. infantum inhibition assay, compounds 7d, 7g and 7c displayed potent inhibition of promastigotes (EC₅₀ 1.59, 1.47 and 3.73 µM respectively) and amastigotes (EC₅₀ 1.4, 1.9 and 2.6 µM respectively). SAR studies revealed that, para substitution of methoxy, chloro groups and methyl group on ortho position favored anti-leishmanial activity against L. infantum. Among these analogues 7d, 7h, 7n and 7g exhibited potent inhibition against L. donovani promastigotes (EC₅₀ 0.91, 4.0, 4.57 and 5.02 µM respectively), axenic amastigotes (EC₅₀ 0.9, 3.5, 2.2 and 3.8 µM respectively) and intracellular amastigotes (EC₅₀ 1.3, 7.8, 5.6 and 6.3 µM respectively). SAR studies suggested that, para substitution of methoxy group, para and meta substitution of chloro groups and benzyl replacement recommended for significant anti-leishmanial against L. donovani.

Active Natural Product Scaffolds against Trypanosomatid Parasites: A Review

Neglected tropical diseases caused by trypanosomatid parasites are a continuing and escalating problem, which devastate the less economically developed cultures in countries in which they are endemic by impairing both human and animal health. Current drugs for these diseases are regarded as out-of-date and expensive, with unacceptable side-effects and mounting parasite resistance, meaning there is an urgent need for new therapeutics. Natural products have long been a source of potent, structurally diverse bioactive molecules. Herein are reviewed natural products with reported trypanocidal activity, which have been clustered based on core structural similarities, to aid the future discovery of new trypanocidal core motifs with potential routes to synthetically accessible natural product cores suggested.

CuBr2-Catalyzed Mild Oxidation of 3,4-Dihydro-β-Carbolines and Application in Total Synthesis of 6-Hydroxymetatacarboline D

A green chemical method for the conversion of 3,4-dihydro-β-carbolines to β-carbolines has been developed using air as the oxidant. With 15 mol % CuBr₂ as the catalyst, 3,4-dihydro-β-carbolines could be efficiently oxidized to β-carbolines in dimethyl sulfoxide at room temperature in the presence of 1,8-diazabicyclo[5,4,0]undec-7-ene (or Et₃N). By applying this method, the first total synthesis of 6-hydroxymetatacarboline D was performed through 12 steps in 22% overall yield starting from l-5-hydroxy-tryptophan.

An insight into tetrahydro-β-carboline-tetrazole hybrids: synthesis and bioevaluation as potent antileishmanial agents

A series of 2,3,4,9-tetrahydro-β-carboline tetrazole derivatives (14a-u) have been synthesized utilizing the Ugi multicomponent reaction and were identified as potential antileishmanial chemotypes. Most of the screened derivatives exhibited significant in vitro activity against the promastigote (IC₅₀ from 0.59 ± 0.35 to 31 ± 1.27 μM) and intracellular amastigote forms (IC₅₀ from 1.57 ± 0.12 to 17.6 ± 0.2 μM) of L. donovani, and their activity is comparable with standard drugs miltefosine and sodium stibogluconate. The most active compound 14t was further studied in vivo against the L. donovani/golden hamster model at a dose of 50 mg kg^-1 through the intraperitoneal route for 5 consecutive days, which displayed 75.04 ± 7.28% inhibition of splenic parasite burden. Pharmacokinetics of compound 14t was studied in the golden Syrian hamster, and following a 50 mg kg^-1 oral dose, the compound was detected in hamster serum for up to 24 h. It exhibited a large volume of distribution (651.8 L kg^-1), high clearance (43.2 L h^-1 kg^-1) and long mean residence time (10 h).

Gamma irradiation of medicinally important plants and the enhancement of secondary metabolite production

PURPOSE

The profitable production of some important plant-based secondary metabolites (ginsenosides, saponins, camptothecin, shikonins etc.) in vitro by gamma irradiation is a current area of interest. We reviewed different types of secondary metabolites, their mode of synthesis and effect of γ-radiation on their yield for different plants, organs and in vitro cultures (callus, suspension, hairy root). Special effort has been made to review the biochemical mechanisms underlying the increase in secondary metabolites. A comparison of yield improvement with biotic and abiotic stresses was made.

RESULTS

Phenolic compounds increase with γ-irradiation in whole plants/plant parts; psoralen content in the common herb babchi (Psoralea corylifolia) was increased as high as 32-fold with γ-irradiation of seeds at 20 kGy. The capsaicinoids, a phenolic compound increased about 10% with 10 kGy in paprika (Capsicum annum L.). The in vitro studies show all the three types of secondary metabolites are reported to increase with γ-irradiation. Stevioside, total phenolic and flavonoids content were slightly increased in 15 Gy-treated callus cultures of stevia (Stevia rebaudiana Bert.). In terpenoids, total saponin and ginsenosides content were increased 1.4- and 1.8-fold, respectively, with 100 Gy for wild ginseng (Panax ginseng Meyer) hairy root cultures. In alkaloids, camptothecin yield increased as high as 20-fold with 20 Gy in callus cultures of ghanera (Nothapodytes foetida). Shikonins increased up to 4-fold with 16 Gy in suspension cultures of purple gromwell (Lithospermum erythrorhizon S.). The enzymes associated with secondary metabolite production were increased with γ-irradiation of 20 Gy; namely, phenylalanine ammonia-lyase (PAL) for phenolics, chalcone synthase (CHS) for flavonoids, squalene synthase (SS), squalene epoxidase (SE) and oxidosqualene cyclases (OSC) for ginsenosides and PHB (p-hydroxylbenzoic acid) geranyl transferase for shikonins.

CONCLUSIONS

An increase in secondary metabolites in response to various biotic and abiotic stresses is compared with ionizing radiation. A ∼5- to 20-fold increase is noted with ∼20 Gy irradiation dose. It increases the yield of secondary metabolites by enhancing the activity of certain key biosynthetic enzymes. Identification of the optimum dose is the important step in the large-scale production of secondary metabolites at industrial level.

Manzamine Alkaloids from an Acanthostrongylophora sp. Sponge

Five new manzamine alkaloids (1-5) and new salt forms of two known manzamines (6 and 7), along with seven known compounds (8-14) of the same structural class, were isolated from an Indonesian Acanthostrongylophora sp. sponge. On the basis of the results of combined spectroscopic analyses, the structure of kepulauamine A (1) was determined to possess an unprecedented pyrrolizine moiety, while others were functional group variants of known manzamines. These compounds exhibited weak cytotoxicity, moderate antibacterial activity, and mild inhibition against the enzyme isocitrate lyase.

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.

Antifungal potential of marine natural products

Fungal diseases represent an increasing threat to human health worldwide which in some cases might be associated with substantial morbidity and mortality. However, only few antifungal drugs are currently available for the treatment of life-threatening fungal infections. Furthermore, plant diseases caused by fungal pathogens represent a worldwide economic problem for the agriculture industry. The marine environment continues to provide structurally diverse and biologically active secondary metabolites, several of which have inspired the development of new classes of therapeutic agents. Among these secondary metabolites, several compounds with noteworthy antifungal activities have been isolated from marine microorganisms, invertebrates, and algae. During the last fifteen years, around 65% of marine natural products possessing antifungal activities have been isolated from sponges and bacteria. This review gives an overview of natural products from diverse marine organisms that have shown in vitro and/or in vivo potential as antifungal agents, with their mechanism of action whenever applicable. The natural products literature is covered from January 2000 until June 2015, and we are reporting the chemical structures together with their biological activities, as well as the isolation source.

Diversity oriented synthesis of β-carbolinone and indolo-pyrazinone analogues based on an Ugi four component reaction and subsequent cyclisation of the resulting indole intermediate

One pot two step synthesis of β-carbolinone and indolo-pyrazinone analogues via acid mediated cyclisation of Ugi intermediate has been developed with a wide substrate scope.