Ecteinascidins 729, 743, 745, 759A, 759B, and 770: potent antitumor agents from the Caribbean tunicate Ecteinascidia turbinata [Erratum to document cited in CA113(9):75189d]

Recent advances in the synthesis and activity of analogues of bistetrahydroisoquinoline alkaloids as antitumor agents

Ecteinascidin 743 (Et-743), also known by the trade name Yondelis®, is the pioneering marine natural product to be successfully developed as an antitumor drug. Moreover, it is the first tetrahydroisoquinoline natural product used clinically for antitumor therapy since Kluepfel, a Canadian scientist, discovered the tetrahydroisoquinoline alkaloid (THIQ) naphthyridinomycin in 1974. Currently, almost a hundred natural products of bistetrahydroisoquinoline type have been reported. Majority of these bistetrahydroisoquinoline alkaloids exhibit diverse pharmacological activities, with some family members portraying potent antitumor activities such as Ecteinascidins, Renieramycins, Saframycins, Jorumycins, among others. Due to the unique chemical structure and exceptional biological activity of these natural alkaloids, coupled with their scarcity in nature, research seeking to provide material basis for further bioactivity research through total synthesis and obtaining compound leads with medicinal value through structural modification, remains a hot topic in the field of antitumor drug R&D. Despite the numerous reviews on the total synthesis of bistetrahydroisoquinoline natural products, comprehensive reviews on their structural modification are apparently scarce. Moreover, structural modification of bioactive natural products to acquire lead compounds with improved pharmaceutical characteristics, is a crucial approach for innovative drug discovery. This paper presents an up-to-date review of both structural modification and activity of bistetrahydroisoquinoline natural products. It highlights how such alkaloids can be used as antitumor lead compounds through careful chemical modifications. This review offers valuable scientific references for pharmaceutical chemists engaged in developing novel antitumor agents based on such alkaloid modifications, as well as those with such a goal in future.

Dearomative logic in natural product total synthesis

Covering: 2011 to 2022The natural world is a prolific source of some of the most interesting, rare, and complex molecules known, harnessing sophisticated biosynthetic machinery evolved over billions of years for their production. Many of these natural products represent high-value targets of total synthesis, either for their desirable biological activities or for their beautiful structures outright; yet, the high sp³-character often present in nature's molecules imparts significant topological complexity that pushes the limits of contemporary synthetic technology. Dearomatization is a foundational strategy for generating such intricacy from simple materials that has undergone considerable maturation in recent years. This review highlights the recent achievements in the field of dearomative methodology, with a focus on natural product total synthesis and retrosynthetic analysis. Disconnection guidelines and a three-phase dearomative logic are described, and a spotlight is given to nature's use of dearomatization in the biosynthesis of various classes of natural products. Synthetic studies from 2011 to 2021 are reviewed, and 425 references are cited.

Marine Invertebrate Metabolites with Anticancer Activities: Solutions to the "Supply Problem"

Marine invertebrates provide a rich source of metabolites with anticancer activities and several marine-derived agents have been approved for the treatment of cancer. However, the limited supply of promising anticancer metabolites from their natural sources is a major hurdle to their preclinical and clinical development. Thus, the lack of a sustainable large-scale supply has been an important challenge facing chemists and biologists involved in marine-based drug discovery. In the current review we describe the main strategies aimed to overcome the supply problem. These include: marine invertebrate aquaculture, invertebrate and symbiont cell culture, culture-independent strategies, total chemical synthesis, semi-synthesis, and a number of hybrid strategies. We provide examples illustrating the application of these strategies for the supply of marine invertebrate-derived anticancer agents. Finally, we encourage the scientific community to develop scalable methods to obtain selected metabolites, which in the authors' opinion should be pursued due to their most promising anticancer activities.

Total synthesis of ecteinascidin 743

A convergent total synthesis of ecteinascidin 743 is realized from five building blocks of almost equal size. It takes 23 steps from l-3-hydroxy-4-methoxy-5-methyl phenylalanol (5) with an overall yield of 3%.

Synthetic studies toward ecteinascidin 743

An efficient synthesis of a fully functionalized tetracycle (A-B-C-H) 7 containing a 1,4-bridged 10-membered lactone was developed. Phenolic aldol condensation between 2-methylsesamol (15) and Garner's aldehyde provided the protected amino diol 16, which was converted to free amine 11 in excellent yield. A Pictet-Spengler reaction between 11 and ethyl glyoxylate under carefully controlled conditions (LiCl, toluene, 1,1,1,3,3,3-hexafluoro-2-propanol, room temperature) provided the acid-sensitive tetrahydroisoquinoline (18) in high yield, which was converted to the amino alcohol 9. Enantioselective alkylation of a glycine template in the presence of a catalytic amount of chiral cinchonidium salt was the key step for the access of enantiomerically pure amino aldehyde 10. Union of the two fragments 9 and 10 via oxazolidine intermediate afforded amino nitrile 39, which upon esterification of the primary alcohol with (R)-N-(S-4,4',4' '-trimethoxyltrityl) Cys (42) afforded 43. Cyclization of 43 (1% trifluoroacetic acid in trifluoroethanol) provided compound 44 by a domino process involving (a) unmasking of the S-trimethoxytrityl group, (b) fragmentation of dioxane assisted by an electron-rich aromatic ring, and (c) formation of a 1,4-bridged 10-membered lactone via formation of a sulfide linkage. Treatment of 7, obtained in two steps from 44b, under acidic conditions (0.5% methyl sulfonic acid in acetonitrile) afforded the pentacyclic compound 51 via fragmentation of the 10-membered cyclic sulfide followed by an intramolecular Pictet-Spengler reaction.

Marine natural products

This review covers the literature published in 2003 for marine natural products, with 619 citations (413 for the period January to December 2003) referring to compounds isolated from marine microorganisms and phytoplankton, green algae, brown algae, red algae, sponges, coelenterates, bryozoans, molluscs, tunicates and echinoderms. The emphasis is on new compounds (656 for 2003), together with their relevant biological activities, source organisms and country or origin. Biosynthetic studies or syntheses that lead to the revision of structures or stereochemistries have been included (78), including any first total syntheses of a marine natural product.

Conicamin, a novel histamine antagonist from the mediterranean tunicate Aplidium conicum

In addition to the known 6-bromo-hypaphorine (2) and plakohypaphorine-A (3), the methanol extract of the Mediterranean tunicate Aplidium conicum was shown to contain conicamin, a novel indole alkaloid having histamine-antagonistic activity which structure was determined to be 1 on the basis of the spectral data.

Solid-phase total synthesis of trunkamide A(1)

Marine organisms are a rich source of novel, biologically active compounds. Herein, the solid-phase total synthesis of trunkamide A, currently in preclinical trials, is presented. Trunkamide A contains a thiazoline heterocycle and two residues of Ser and Thr with the hydroxy function modified as reverse prenyl (rPr). Cornerstones of the synthesis are as follows: (i) solid-phase peptide chain elongation using a quasi-orthogonal protecting scheme with tert-butyl and fluorenyl based groups, on a chlorotrityl resin; (ii) concourse of HOAt-based coupling reagents; and (iii) cyclizations in solution. Furthermore, the following synthetic steps are discussed: (i) preparation of the reverse prenyl derivatives of Ser and Thr; (ii) introduction of precursor of thiazoline as a protected amino thionoacid derivative; and (iii) formation of the thiazoline ring with DAST. All these features make this strategy particularly suitable for the large-scale synthesis of trunkamide A and other peptides containing the same motifs.