Some pharmacological activities of novel adenine-related compounds isolated from a marine sponge Agelas mauritiana

Synthesis of pyrimidine-containing alkaloids

This review deals with the synthesis of naturally occurring alkaloids containing partially or completely saturated pyrimidine nuclei. The interest in these compounds is associated with their structural diversity, high biological activity and toxicity. The review is divided into four parts, each of which describes a number of synthetic methodologies toward structurally different naturally occurring alkaloids containing saturated cyclic six-membered amidine, guanidine, aminal and urea (thiourea) moieties, respectively. The development of various synthetic strategies for the preparation of these compounds has remarkably increased during the past few decades. This is primarily due to the fact that some of these compounds are isolated only in limited quantities, which makes it practically impossible to study their full structural characteristics and biological activity.

Secondary metabolites from marine sponges of the genus Agelas: a comprehensive update insight on structural diversity and bioactivity

As one of the most common marine sponges in tropical and subtropical oceans, the sponges of the genus Agelas, have emerged as unique and yet under-investigated pools for discovery of natural products with fabulous molecular diversity and myriad interesting biological activities. The present review highlights the chemical structure and biological activity of 355 compounds that have been isolated and characterized from the members of Agelas sponges, over the period of about five decades (from 1971 to November 2021). For a better understanding, these numerous compounds are firstly classified and presented according to their carbon skeleton as well as their biosynthetic origins. Relevant summaries focusing on the source organism and the associated bioactivity of these compounds belonging to different chemical classes are also provided. This review highlights sponges of the genus Agelas as exciting source for discovery of intriguing natural compounds.

The marine sponges of the genus Agelas, are unique and yet under-investigated pools for discovery of natural products with fabulous molecular diversity and myriad interesting biological activities.

Marine Alkylpurines: A Promising Group of Bioactive Marine Natural Products

Marine secondary metabolites with a purine motif in their structure are presented in this review. The alkylpurines are grouped according to the size of the alkyl substituents and their location on the purine ring. Aspects related to the marine source, chemical structure and biological properties are considered together with synthetic approaches towards the natural products and bioactive analogues. This review contributes to studies of structure–activity relationships for these metabolites and highlights the potential of the sea as a source of new lead compounds in diverse therapeutic fields.

Bioactive Secondary Metabolites from the Marine Sponge Genus Agelas

The marine sponge genus Agelas comprises a rich reservoir of species and natural products with diverse chemical structures and biological properties with potential application in new drug development. This review for the first time summarized secondary metabolites from Agelas sponges discovered in the past 47 years together with their bioactive effects.

A new species of Agelas from the Zanzibar Archipelago, western Indian Ocean (Porifera, Demospongiae)

A new sponge species (Demospongiae: Agelasida: Agelasidae) is described from the eastern coast of Unguja Island in the Zanzibar Archipelago. Agelassansibaricasp. n. is compared to all other Agelas species described so far. The new species differs from its congeners mainly in its three categories of verticillate spicules (acanthostyles, acanthostrongyles, and acanthoxeas) and their sizes. Acanthostrongyles, well represented in the spicular complement, are an exclusive trait of the new species widening the morphological range of the genus. Summarizing on spicular complement and spicular morphotraits of 36 species belonging to the genus Agelas: i) 32 species show only acanthostyles from Indo-Pacific (n = 14), Atlantic (n = 17), and Mediterranean (n = 1); ii) three Indo-Pacific species show acanthostyles and acanthoxeas; iii) one species Agelassansibaricasp. n. from the western Indian Ocean is characterised by the unique trait of three categories of verticillate spicules (acanthostyles, acanthostrongyles and acanthoxeas). A key for the Indo-Pacific species is supplied together with short descriptions, illustrations, and geographic range; literature on chemical bioprospecting of the genus Agelas is also provided.

Nitrosopurines en route to potently cytotoxic asmarines

A nitrosopurine ene reaction easily assembles the asmarine pharmacophore and transmits remote stereochemistry to the diazepine-purine hetereocycle. This reaction generates potent cytotoxins which exceed the potency of asmarine A (1.2 μM IC50) and supersede the metabolites as useful leads for biological discovery.

Terpenyl-purines from the sea

Agelasines, asmarines and related compounds are natural products with a hybrid terpene-purine structure isolated from numerous genera of sponges (Agela sp., Raspailia sp.). Some agelasine analogs and related structures have displayed high general toxicity towards protozoa, and have exhibited broad-spectrum antimicrobial activity against a variety of species, including Mycobacterium tuberculosis, and also an important cytotoxic activity against several cancer cell lines, including multidrug-resistant ones. Of particular interest in this context are the asmarines (tetrahydro[1,4]diazepino[1,2,3-g,h]purines), which have shown potent antiproliferative activity against several types of human cancer cell lines. This review summarizes the sources of isolation, chemistry and bioactivity of marine alkylpurines and their bioactive derivatives.

Screening of agelasine D and analogs for inhibitory activity against pathogenic protozoa; identification of hits for visceral leishmaniasis and Chagas disease

There is an urgent need for novel and improved drugs against several tropical diseases caused by protozoa. The marine sponge (Agelas sp.) metabolite agelasine D, as well as other agelasine analogs and related structures were screened for inhibitory activity against Plasmodium falciparum, Leishmania infantum, Trypanosoma brucei and T. cruzi, as well as for toxicity against MRC-5 fibroblast cells. Many compounds displayed high general toxicity towards both the protozoa and MRC-5 cells. However, two compounds exhibited more selective inhibitory activity against L. infantum (IC₅₀ <0.5 μg/mL) while two others displayed IC₅₀ <1 μg/mL against T. cruzi in combination with relatively low toxicity against MRC-5 cells. According to criteria set up by the WHO Special Programme for Research & Training in Tropical Diseases (TDR), these compounds could be classified as hits for leishmaniasis and for Chagas disease, respectively. Identification of the hits as well as other SAR data from this initial screening will be valuable for design of more potent and selective potential drugs against these neglected tropical diseases.

Synthesis, antimicrobial and antineoplastic activities for agelasine and agelasimine analogs with a beta-cyclocitral derived substituent

Agelasines and agelasimines are antimicrobial and cytotoxic purine derivatives isolated from marine sponges (Agelas sp.). We have synthesized structurally simplified analogs of these natural products starting from beta-cyclocitral. The novel compounds were found to be strong inhibitors of a wide variety of pathogenic microorganisms (incl. Mycobacterium tuberculosis) as well as cancer cell lines. The biological activities were generally in the same range as those previously found for the structurally more complex agelasines and agelasimines isolated in small amounts from natural sources. We also report for the first time that agelasine and agelasimine analogs inhibit growth of protozoa (Acanthamoeba castellanii and Acanthamoeba polyphaga). Acanthamoeba keratitis is an increasingly common and severe corneal infection, closely associated with contact lens wear.

Antifouling activity of the sponge metabolite agelasine D and synthesised analogs on Balanus improvisus

This study reports a screening study for antifouling (AF) activity of the natural compound agelasine D isolated from marine sponges of the genus Agelas and 20 synthesised analogs of agelasines and agelasimines. Agelasine D, together with two of the analogs, ie AV1003A and AKB695, displayed a strong inhibitory effect on settlement of Balanus improvisus cypris larvae. Agelasine D had an EC50 value of 0.11 microM while the two analogs AV1033A and AKB695 had EC50 values of 0.23 and 0.3 microM, respectively. None of these three compounds affected larval mortality as was the case with several of the analogs tested. Moreover, the effect of AV1033A and AKB695 was reversible. When cyprids after 24 h exposure to the compounds were transferred to fresh seawater, the settlement frequency compared with the controls was completely recovered. The properties of the agelasine D analogs AV1003A and AKB695 make them highly attractive candidates as AF agents in future marine coatings.

Antimicrobial and cytotoxic activity of agelasine and agelasimine analogs

Agelasine and agelasimine derivatives with substantially less complicated terpenoid side chains compared to the naturally occurring compounds have been synthesized and their ability to inhibit growth of microorganisms and cancer cells has been studied. Compounds with excellent activity against cancer cell lines (MIC ca. 1 microM for the most potent compounds), including a drug resistant renal cell line, have been identified. Most compounds studied also exhibited broad spectrum antimicrobial activity including activity against Mycobacterium tuberculosis.

Application of a radioreceptor assay to the screening and characterisation of compounds from marine organisms with activity at the phorbol ester binding site of protein kinase C

Protein kinase C is a ubiquitous enzyme with a key role in cellular function, making it an attractive drug target. Utilising a competitive binding assay for the phorbol ester binding site of the enzyme in a rat brain membrane preparation, screening was undertaken on 686 marine macroorganisms representing a broad range of taxa and environments from throughout Australasia. Of these extracts from 28 organisms significantly inhibited [3H]phorbol dibutyrate binding, while two samples enhanced binding. Sponges and echinoderms were particularly well represented in the active specimens. A combination of taxonomic and elution information for individual leads provided a rationale for dereplication and prioritisation. Utilising assay-guided purification, the identity of active compounds from the sponge Agelas axifera was examined in detail. The previously described compounds, the agelasines, were identified. The screening and characterisation methods described provide a method for readily identifying novel probes for protein kinase C.

Identification of marine organism extracts active at the EGF binding site of human A431 cells

Using a high throughput radioligand binding assay, we assessed aqueous ethanol extracts from 2885 marine organisms representing 17 phyla from the Indo-Pacific for their capacity to influence [125I]epidermal growth factor binding to human A431 cells in culture. Initial screening employed extracts pooled from five unrelated organisms to cells incubated at 37 degrees C for 20 min. Positive leads from the low stringency screening were pursued using extracts from individual organisms. Extracts from 57 organisms significantly inhibited radioligand binding, five organisms caused the cells to detach from the substrate, while extracts from two organisms brought about an increase in bound radiolabel. To discriminate between the mechanisms of action of the extracts, active organisms were also tested for their capacity to affect radioligand binding in the cells when incubated at 4 degrees C. Those organisms acting only at 37 degrees C were considered to have a cellular site of action, while those also active at the low temperature were considered to exert their effects more directly on the receptor binding event. The acute biochemical activity elicited by the positive organisms was distributed widely between taxa and between geographic regions. The approach provides a sensitive, high volume assay for detecting bioactive substances within marine organisms.