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This review covers recent literature from 2012-2019 concerning 170 marine natural products and their semisynthetic analogues with strong anticancer biological activities. Reports that shed light on cellular and molecular mechanisms and biological functions of these compounds, thus advancing the understanding in cancer biology are also included. Biosynthetic studies and total syntheses, which have provided access to derivatives and have contributed to the proper structure or stereochemistry elucidation or revision are mentioned. The natural compounds isolated from marine organisms are divided into nine groups, namely: alkaloids, sterols and steroids, glycosides, terpenes and terpenoids, macrolides, polypeptides, quinones, phenols and polyphenols, and miscellaneous products. An emphasis is placed on several drugs originating from marine natural products that have already been marketed or are currently in clinical trials.

We report here on the synthesis and in vitro anti-tumor effects of a series of novel 1,2,4-triazole (compounds 3–6), 4,5-dicyanoimidazole (compound 7), and purine (compounds 8–13) coumarin derivatives and their acyclic nucleoside analogues 14–18. Structures of novel compounds 3–18 were deduced from their 1H- and 13C-NMR and corresponding mass spectra. Results of anti-proliferative assays performed on a panel of selected human tumor cell lines revealed that compound 6 had moderate cytostatic activity against the HeLa cell line (IC50 = 35 µM), whereas compound 10 showed moderate activity against the HeLa (IC50 = 33 µM), HepG2 (IC50 = 25 µM) and SW620 (IC50 = 35 µM) cell lines. These compounds showed no cytotoxic effects on normal (diploid) human fibroblasts.

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In spite of significant advancements and success in antiretroviral therapies directed against HIV infection, there is no cure for HIV, which scan persist in a human body in its latent form and become reactivated under favorable conditions. Therefore, novel antiretroviral drugs with different modes of actions are still a major focus for researchers. In particular, novel lead structures are being sought from natural sources. So far, a number of compounds from marine organisms have been identified as promising therapeutics for HIV infection. Therefore, in this paper, we provide an overview of marine natural products that were first identified in the period between 2013 and 2018 that could be potentially used, or further optimized, as novel antiretroviral agents. This pipeline includes the systematization of antiretroviral activities for several categories of marine structures including chitosan and its derivatives, sulfated polysaccharides, lectins, bromotyrosine derivatives, peptides, alkaloids, diterpenes, phlorotannins, and xanthones as well as adjuvants to the HAART therapy such as fish oil. We critically discuss the structures and activities of the most promising new marine anti-HIV compounds.

Evaluation of their affinity for herpes simplex type 1 (HSV-1) and varicella-zoster virus-encoded thymidine kinases (VZV TK) also showed that none of the compounds was able to significantly inhibit 1 µM deoxythymidine phosphorylation by HSV-1 and VZV TK at 500 µM concentrations. The in vitro cytostatic activity evaluation results indicated a weak antiproliferative activity for all tested compounds. Only 6-pyrrolylpurine derivative bearing a carboxylic group substituted cyclopropane ring produced a rather slight inhibitory effect at higher micromolar concentrations on a breast carcinoma cell line (MCF-7) and no cytotoxic effect on human normal fibroblasts (WI 38). Conclusions: The lack of antiherpetic activity may be due to poor, if any, recognition of the compounds by virus-induced nucleoside kinases as an alternative substrate to become metabolically activated.The discovery of the acyclic guanosine analogue acyclovir (ACV; Figure 1) as a selective anti-herpes simplex virus (HSV) agent [1] initiated investigation of new acyclic nucleoside analogues with better antiviral activity properties than ACV. These efforts resulted in the discovery of new broad-spectrum antiviral agents: ganciclovir (GCV; Figure 1) [2][3][4] and penciclovir (PCV; Figure 1) [5,6]. In addition, the crystal structure of HSV-1-encoded thymidine kinase (TK), a key enzyme for activation of antiherpetic nucleosides, in complex with GCV, revealed the importance of the two hydroxyl groups of GCV mimicking the 3′-and 5′-hydroxyl groups of the 2′-deoxyribose moiety in natural nucleosides for substrate recognition [7].Based on these findings, (1′S, 2′R)-9-{[1′,2′-bis(hydroxymethyl)cycloprop-1-yl]methyl}guanine (A-5021; Figure 2) was developed as a nucleoside analogue that potently inhibits the replication of several herpes viruses including HSV type-1 (HSV-1) and HSV type-2 (HSV-2), varicella-zoster virus (VZV), Epstein-Barr virus (EBV) and human herpesvirus type 6 (HHV-6). Though the sugar moiety of A-5021 has a cyclopropane ring, its overall feature is considered to be acyclic due to the flexible methylenic spacer. The antiviral activity of A-5021 is superior over ACV against HSV-1, HSV-2, . The racemic 9-{[1′,2′-bis(hydroxymethyl)cycloprop-1-yl] methyl}guanine and especially its 1′S, 2′R enantiomer