Synthesis and biological activities of [N-MeLeu5] didemnin B

Total Synthesis and Biological Evaluation of Tamandarin B Analogues

Tamandarins A and B are a class of marine natural cyclodepsipeptides with structures and biological activities closely related to those of the didemnins. The easier synthetic access to tamandarins accelerates the preparation of new macrocyclic derivatives of this family of antitumor, antiviral, and immunosuppressive compounds. The optimization of the previously reported synthetic route to tamandarins by changing the macrolactamization site from Nst1 and Thr6 to Pro4 and N,O-Me2Tyr5 residues led to a significant improvement in the reaction yield. Using this new synthetic approach, four new macrocyclic analogues of tamandarin B were prepared and evaluated for anticancer activity. These results provide further insight into the structure-activity relationship of the tamandarins and didemnins.

Synthesis and biological evaluation of tamandarin B analogues

[structure: see text]. The synthesis of two tamandarin B analogues in which the N,O-Me2Tyr5 unit was replaced by N-Me-phenylalanine (N-MePhe5) and (S)-2-(methylamino)-3-(naphthalen-2-yl)propanoic acid (N-MeNaphth5) is described. The choice of the macrocyclization site was crucial to achieve satisfactory macrolactamization. Coupling between norstatine (Nst1) and threonine (Thr6) afforded only a 15% yield, while lactamization between proline (Pro4) and the aromatic moiety could be achieved in 65% yield.

Natural products as probes of cell biology: 20 years of didemnin research

The discovery of the didemnin family of marine depsipeptides launched an exciting and intriguing chapter in natural product chemistry. The unusual structure of the didemnin congeners has led to several total syntheses by research groups from around the world. The impressive in vitro and in vivo biological activities of the didemnins resulted in the first human clinical trials in the U.S. of a marine natural product against cancer, and additional clinical trials of a second-generation didemnin, dehydrodidemnin B (aplidine), are underway. As we mark the 20-year anniversary of the discovery of the didemnins, this class of natural products continues to stimulate active research in fields ranging from synthetic and medicinal chemistry to clinical oncology and cell biology. While some progress was made in dissecting the molecular mechanism of action and in establishing structure-activity relationships, there are still more questions than answers. This review covers the recent didemnin literature, highlighting the work directed towards understanding how this group of natural products interact with fundamental processes such as cell proliferation, protein biosynthesis, and apoptosis. The didemnin field illustrates how natural product chemistry may be used as a critical tool for the study of cell biology.

Total syntheses of conformationally constrained didemnin B analogues. replacements of N,O-dimethyltyrosine with L-1,2,3,4-tetrahydroisoquinoline and L-1,2,3,4-tetrahydro-7-methoxyisoquinoline

The design and synthesis of two conformationally constrained analogues of didemnin B are described. The [N,O-Me(2)Tyr(5)]residue of didemnin B was replaced with L-1,2,3,4-tetrahydroisoquinoline-3-carboxylic acid (Tic) and L-1,2,3,4-tetrahydro-7-methoxyisoquinoline-3-carboxylic acid (MeO-Tic), which mimic the N,O-dimethylated tyrosine while constraining the conformation of the molecule. Preliminary results indicate that the conformation of the [N,O-Me(2)Tyr(5)]residue closely matches the conformation imposed by the Tic replacement.

Tamandarins A and B: new cytotoxic depsipeptides from a Brazilian ascidian of the family Didemnidae

The structures of two new, naturally occurring cytotoxic depsipeptides, tamandarins A and B (1 and 2), are presented. The tamandarins were isolated from an unidentified Brazilian marine ascidian of the family Didemnidae. The structures of the new cytotoxins were assigned by interpretation of FABMS data and by extensive 2D NMR analyses. The absolute configurations of the tamandarins were assigned by acid and alkaline hydrolysis to yield their corresponding amino acids, which were then analyzed as their Marfey derivatives. The cytotoxicity of tamandarin A (1) was evaluated against various human cancer cell lines and shown to be slightly more potent than didemnin B. A qualitative discussion of the conformation of tamandarin A (1) in solution, obtained from NMR J-value data, variable temperature experiments, and NOESY/ROESY data, is included.

Synthesis and biological activity of [Tic5] didemnin B

A didemnin B analog containing a Tic (1,2,3,4-tetrahydroisoquinoline-3-carboxylic acid) as a conformationally restrained replacement for tyrosine has been synthesized and shown to have comparable potency as a protein biosynthesis inhibitor. Synthetic highlights include an oxidation of an alcohol to an acid in the presence of the sensitive Tic heterocycle and a modified Schmidt-type one-pot macrocyclization.