A stereoselective synthesis of the C-10 to C-18 (right-half) fragment of mycalamides employing lewis acid promoted intermolecular aldol reaction

Pederin, Psymberin and the Structurally Related Mycalamides: Synthetic Aspects and Biological Activities

Pederin, psymberin, and mycalamides are related members of a relatively new family of potent natural antiviral and antitumor compounds originally isolated from marine sponges in 1988. This natural family of chemicals is of great interest to medicinal chemists and biologists, stemming from its extremely low abundance in source organisms and strikingly potent biological activity. They have clearly emerged as promising new synthetic targets, and are the focus of quite an interdisciplinary approach to molecular characterization. In this chapter we review diverse synthetic approaches to this family of natural products that has been demonstrating remarkable biological activity. We discuss relevant history, biological origins with the latest information on source organisms and their hosts, in-depth synthetic approaches, and biological data supporting their potential as therapeutic compounds.

Antiviral lead compounds from marine sponges

Marine sponges are currently one of the richest sources of pharmacologically active compounds found in the marine environment. These bioactive molecules are often secondary metabolites, whose main function is to enable and/or modulate cellular communication and defense. They are usually produced by functional enzyme clusters in sponges and/or their associated symbiotic microorganisms. Natural product lead compounds from sponges have often been found to be promising pharmaceutical agents. Several of them have successfully been approved as antiviral agents for clinical use or have been advanced to the late stages of clinical trials. Most of these drugs are used for the treatment of human immunodeficiency virus (HIV) and herpes simplex virus (HSV). The most important antiviral lead of marine origin reported thus far is nucleoside Ara-A (vidarabine) isolated from sponge Tethya crypta. It inhibits viral DNA polymerase and DNA synthesis of herpes, vaccinica and varicella zoster viruses. However due to the discovery of new types of viruses and emergence of drug resistant strains, it is necessary to develop new antiviral lead compounds continuously. Several sponge derived antiviral lead compounds which are hopedto be developed as future drugs are discussed in this review. Supply problems are usually the major bottleneck to the development of these compounds as drugs during clinical trials. However advances in the field of metagenomics and high throughput microbial cultivation has raised the possibility that these techniques could lead to the cost-effective large scale production of such compounds. Perspectives on biotechnological methods with respect to marine drug development are also discussed.

Studies toward the asymmetric synthesis of the right part of the mycalamides

Described herein is the asymmetric synthesis of a functionalized, trioxadecalin unit that comprises the right-hand part of the mycalamides and related natural products. The synthetic route involves a 16-step sequence that accomplishes the formation of two heterocyclic rings and the generation of five stereocenters. The synthesis commenced with a C2-symmetric starting material, diethyl D-tartrate, and took advantage of a relay of diastereoselective reactions to extend this four-carbon chain and introduce new chiral centers. Subsequent electrophile-mediated cyclization afforded the desired pyran ring, which was then transformed into the desired, functionalized trioxadecalin skeleton.

Total synthesis and initial biological evaluation of new B-ring-modified bryostatin analogs

[Structure: see text] The total synthesis and preliminary biological evaluation of the first bryostatin analogs (bryologs) to incorporate B-ring substitution are reported. Asymmetric syntheses of two new polyketide "spacer" domains are described, one exploiting the pseudosymmetry of the C1-C13 region. These fragments are convergently joined to the "recognition" domain through a remarkably versatile macrotransacetalization process. The resulting new analogs exhibit potent nanomolar or picomolar affinity to protein kinase C (PKC), comparable to or better than that found for bryostatin.

Total synthesis of mycalamide A

This communication describes a concise and efficient total synthesis of mycalamide A by the convergent coupling of pederic acid unit with the mycalamine unit. The left-half, (+)-7-benzoylpederic acid, was synthesized from (2R,3R)-3-methylpent-4-en-2-ol in seven steps and 34.6% overall yield through a route that features a one-step Pd(II)-catalyzed tandem Wacker/Heck cyclization reaction to prepare the tetrahydropyran ring system. The right-half, the mycalamine unit, was synthesized in 21 steps and 10.5% overall yield from diethyl d-tartrate. Effective, stereoselective methods were developed for the assembly of the two parts to yield either mycalamide A or C(10)-epi-mycalamide A.

Inhibition of protein synthesis and activation of stress-activated protein kinases by onnamide A and theopederin B, antitumor marine natural products

During the course of screening for the agents that activate transforming growth factor-beta (TGF-beta) signaling cascade, onnamide A and theopederin B, heterocyclic compounds related to mycalamides from a marine sponge, were found to induce plasminogen activator inhibitor-1 (PAI-1) promoter-derived gene expression in Mv1Lu cells. The maximum induction of the PAI-1 promoter by onnamide A and theopederin B was observed at the concentrations of 50 nM and 2 nM, respectively. These compounds strongly inhibited protein synthesis at the 50% inhibitory concentrations of 30 nM for onnamide A and 1.9 nM for theopederin B, and induced activation of p38 mitogen-activated protein kinase and c-Jun NH2-terminal protein kinase (JNK). Anisomycin, a well-known inducer of ribotoxic stress that inhibits protein synthesis and activates both p38 kinase and JNK, also activated PAI-1 gene expression. Furthermore, PAI-1 expression by onnamide A, theopederin B, and anisomycin was inhibited by SB202190 and SP600125, specific inhibitors of stress-activated protein kinases. Onnamide A and theopederin B were cytotoxic to a variety of cell lines and strongly induced apoptosis in HeLa cells within 24 h, which was accompanied by the sustained activation of p38 kinase and JNK. These results suggest that onnamide A and theopedirin B trigger a ribotoxic stress-like response, thereby inducing p38 kinase and JNK activation, the kinase-dependent PAI-1 gene expression, and apoptosis.