Total Syntheses of Cyclomarin and Metamarin Natural Products

The first total synthesis of the heptapeptide Cyclomarin A (CymA) was achieved via new routes to chiral amino acid building blocks (highlighted) and solid-phase peptide synthesis. A structurally misassigned epimer of CymA (CymA'), Cyclomarin C, and Metamarin were also synthesized. Affirmation of the syntheses was corroborated by observations that the synthetic molecules have antimicrobial activities mirroring those of the natural products. Interestingly, CymA' is more potent than CymA.

Recent Developments on the Synthesis and Bioactivity of Ilamycins/Rufomycins and Cyclomarins, Marine Cyclopeptides That Demonstrate Anti-Malaria and Anti-Tuberculosis Activity

Ilamycins/rufomycins and cyclomarins are marine cycloheptapeptides containing unusual amino acids. Produced by Streptomyces sp., these compounds show potent activity against a range of mycobacteria, including multidrug-resistant strains of Mycobacterium tuberculosis. The cyclomarins are also very potent inhibitors of Plasmodium falciparum. Biosynthetically the cyclopeptides are obtained via a heptamodular nonribosomal peptide synthetase (NRPS) that directly incorporates some of the nonproteinogenic amino acids. A wide range of derivatives can be obtained by fermentation, while bioengineering also allows the mutasynthesis of derivatives, especially cyclomarins. Other derivatives are accessible by semisynthesis or total syntheses, reported for both natural product classes. The anti-tuberculosis (anti-TB) activity results from the binding of the peptides to the N-terminal domain (NTD) of the bacterial protease-associated unfoldase ClpC1, causing cell death by the uncontrolled proteolytic activity of this enzyme. Diadenosine triphosphate hydrolase (PfAp3Aase) was found to be the active target of the cyclomarins in Plasmodia. SAR studies with natural and synthetic derivatives on ilamycins/rufomycins and cyclomarins indicate which parts of the molecules can be simplified or otherwise modified without losing activity for either target. This review examines all aspects of the research conducted in the syntheses of these interesting cyclopeptides.

Solid-Phase Total Synthesis of Dehydrotryptophan-Bearing Cyclic Peptides Tunicyclin B, Sclerotide A, CDA3a, and CDA4a using a Protected β-Hydroxytryptophan Building Block

A new approach to the synthesis of Z-dehydrotryptophan (ΔTrp) peptides is described. This approach uses Fmoc-β-HOTrp(Boc)(TBS)-OH as a building block, which is readily prepared in high yield and incorporated into peptides using solid-phase Fmoc chemistry. The tert-butyldimethylsilyl-protected indolic alcohol is eliminated during global deprotection/resin cleavage to give ΔTrp peptides exclusively as the thermodynamically favored Z isomer. This approach was applied to the solid-phase synthesis of tunicyclin B, sclerotide A, CDA3a, and CDA4a.

Synthesis of modified β-methoxyphenylalanines via diazonium chemistry and their incorporation in desoxycyclomarin analogues

Chloramphenicol base is converted into substituted syn-β-methoxyphenylalanins, building blocks of modified cyclomarins.

Total synthesis of cyclomarins A, C and D, marine cyclic peptides with interesting anti-tuberculosis and anti-malaria activities

Cyclomarins are cyclic heptapeptides containing four unusual amino acids.

Total synthesis of desoxycyclomarin C and the cyclomarazines A and B

Removing the β-hydroxy group from the prenylated tryptophan moiety of cyclomarins simplifies the synthesis of these interesting natural products significantly, without having a noteworthy effect on the anti-tuberculosis activity of the cyclomarins.