Structural and biological evaluation of some loloatin C analogues

The Biotechnological Potential of Secondary Metabolites from Marine Bacteria

Marine habitats are a rich source of molecules of biological interest. In particular, marine bacteria attract attention with their ability to synthesize structurally diverse classes of bioactive secondary metabolites with high biotechnological potential. The last decades were marked by numerous discoveries of biomolecules of bacterial symbionts, which have long been considered metabolites of marine animals. Many compounds isolated from marine bacteria are unique in their structure and biological activity. Their study has made a significant contribution to the discovery and production of new natural antimicrobial agents. Identifying the mechanisms and potential of this type of metabolite production in marine bacteria has become one of the noteworthy trends in modern biotechnology. This path has become not only one of the most promising approaches to the development of new antibiotics, but also a potential target for controlling the viability of pathogenic bacteria.

Synthesis and biological evaluation of cyclopeptide GG-8-6 and its analogues as anti-hepatocellular carcinoma agents

GG-8-6, cyclo-(Val-Leu-Pro-Ile-Leu-Leu-Leu-Val-Leu, compound 1), and its twelve analogues (compound 2-13) were synthesized based on the lead compound Grifficyclocin B, a cyclic peptide with anti-tumor activity which was isolated from the plants of Goniothalamus species (Annonaceae). The bioassay results showed that these synthetic cyclopeptides exhibited different extent of cytotoxicity against human hepatocellular carcinoma cell lines. Among them, GG-8-6 (1) was the most active compound with IC₅₀ values of 6.38 μM and 12.22 μM against SMMC-7721 and HepG2, respectively. Further studies on the mechanism demonstrated that GG-8-6 (1) could induce apoptosis and G2/M arrest of HCC cells, and the activation of caspase pathways was probably involved. In vivo anti-tumor experiments showed that GG-8-6 (1) could significantly inhibit the growth of tumor in the mouse xenograft tumor model. At the dose of 40 mg/kg, the inhibition ratio was 67.9% without weight loss. Our results suggested that GG-8-6 (1), a new cyclic peptide, might be a potential candidate for developing new anti-HCC drug in the coming future.

Macrocyclic peptidomimetics with antimicrobial activity: synthesis, bioassay, and molecular modeling studies

Novel, cyclic peptidomimetics were synthesized by facile acylation reactions using benzotriazole chemistry. Microbiological testing of the synthesized compounds revealed an exceptionally high activity against Candida albicans with a minimum inhibitory concentration (MIC) two orders of magnitude lower than the MIC of the antifungal reference drug amphotericin B. A strikingly high activity was also observed against three Gram-negative bacterial strains (Pseudomonas aeruginosa, Klebsiella pneumoniae and Proteus vulgaris), two of which are known human pathogens. Thus the discovered chemotype is a potential polypharmacological agent. The toxicity against mammalian tumor cells was found to be low, as demonstrated in five different human cell lines (HeLa, cervical; PC-3, prostate; MCF-7, breast; HepG2, liver; and HCT-116, colon). The internal consistency of the experimental data was studied using 3D-pharmacophore and 2D-QSAR.

Marine bacterial sources of bioactive compounds

Thousands of novel compounds have been isolated from various marine bacteria and tested for pharmacological properties, many of which are commercially available. Many more are being tested as potential bioactive compound at the preclinical and clinical stages. The growing interest in marine-derived antiviral compounds, along with the development of new technology in marine cultures and extraction, will significantly expedite the current exploration of the marine environment for compounds with significant pharmacological applications, which will continue to be a promising strategy and new trend for modern medicine. Marine actinomycetes and cyanobacteria are a prolific but underexploited source for the discovery of novel secondary metabolites.

C-3 branched δ-3,5-cis- and trans-THF sugar amino acids: synthesis of the first generation of branched homooligomers

This article describes the efficient synthesis of the first generation of branched sugar amino acid (SAA) oligomers in solution phase via two main routes: by the use of a standard coupling reagent and via the use of active ester intermediates. Benzyl-protected dimeric carbopeptoid and methyl-protected dimeric and tetrameric, hexameric and octameric carbopeptoids were obtained from a branched δ-3,5-trans-tetrahydrofuran (THF) SAA and methyl-protected dimeric and tetrameric carbopeptoids were synthesised from a branched δ-3,5-cis-THF SAA. These systems are of interest because of their potential to display foldameric properties reminiscent of those observed in α-peptides and proteins. Amongst their many uses, foldamers provide simpler models in the study of the factors which induce the folding and unfolding of proteins and, ultimately, potential insights into their functioning.

(3R,4R,5R)-5-(Acetamido-meth-yl)-N-benzyl-3,4-dihy-droxy-tetra-hydro-furan-3-carboxamide

X-ray crystallographic analysis with Cu Kα radiation established the relative configurations of the stereogenic centers in the title compound, C(15)H(20)N(2)O(5), and clarified mechanistic ambiguities in the synthesis. The conformation of the five-membered ring approximates twisted, about a C-O bond. The absolute configuration of this carbon-branched dipeptide isostere was known based on the use of d-ribose as the starting material. Refinement of the Flack parameter gave an ambiguous result but the refined Hooft parameter is in agreement with the assumed (d-ribose) absolute structure. The crystal structure consists of N-H⋯O and O-H⋯O hydrogen-bonded bi-layers, with the terminal methyl and phenyl groups forming a hydro-phobic inter-layer inter-face. Some weak C-H⋯O inter-actions are also present.

Novel anti-infective compounds from marine bacteria

As a result of the continuous evolution of microbial pathogens towards antibiotic-resistance, there have been demands for the development of new and effective antimicrobial compounds. Since the 1960s, the scientific literature has accumulated many publications about novel pharmaceutical compounds produced by a diverse range of marine bacteria. Indeed, marine micro-organisms continue to be a productive and successful focus for natural products research, with many newly isolated compounds possessing potentially valuable pharmacological activities. In this regard, the marine environment will undoubtedly prove to be an increasingly important source of novel antimicrobial metabolites, and selective or targeted approaches are already enabling the recovery of a significant number of antibiotic-producing micro-organisms. The aim of this review is to consider advances made in the discovery of new secondary metabolites derived from marine bacteria, and in particular those effective against the so called "superbugs", including methicillin-resistant Staphylococcus aureus (MRSA) and vancomycin resistant enterococci (VRE), which are largely responsible for the increase in numbers of hospital acquired, i.e., nosocomial, infections.