Steric and stereochemical effects on the free-radical bromination of tetracyclic and hexacyclic fragments of the MDR inhibitor N-acetylardeemin

Synthetic Studies toward Dimeric Indole Alkaloids Based on Convergent Synthetic Strategy

The total syntheses of dimeric indole alkaloids, haplophytine, and T988s are described. These dimeric compounds comprising two structurally different indole units are ubiquitous in nature, and many possess pharmaceutically important activities. To realize an efficient chemical synthesis of these dimeric indole alkaloids, the establishment of convergent synthetic strategies and development of new coupling methods are indispensable. The linkage of two highly functionalized units at a late stage of the synthesis frequently induces synthetic problems such as chemoselectivity and steric repulsion. Moreover, although transition metal-catalyzed reactions are usually an effective method for the cross-coupling of two units, the application of these cross-coupling reactions to bond formation involving a sterically hindered C(sp³) is often difficult. Thus, even with precise modern synthetic methods, it is currently difficult to realize convergent syntheses of dimeric indole alkaloids possessing a quaternary carbon linking two units. To combat these synthetic problems, we developed a synthetic method to link two indole units using an Ag-mediated nucleophilic substitution reaction. In this review, we provide a detailed discussion of convergent synthetic strategies and coupling methods for dimeric indole alkaloids.

Use of Bromine and Bromo-Organic Compounds in Organic Synthesis

Bromination is one of the most important transformations in organic synthesis and can be carried out using bromine and many other bromo compounds. Use of molecular bromine in organic synthesis is well-known. However, due to the hazardous nature of bromine, enormous growth has been witnessed in the past several decades for the development of solid bromine carriers. This review outlines the use of bromine and different bromo-organic compounds in organic synthesis. The applications of bromine, a total of 107 bromo-organic compounds, 11 other brominating agents, and a few natural bromine sources were incorporated. The scope of these reagents for various organic transformations such as bromination, cohalogenation, oxidation, cyclization, ring-opening reactions, substitution, rearrangement, hydrolysis, catalysis, etc. has been described briefly to highlight important aspects of the bromo-organic compounds in organic synthesis.

Epidithiodiketopiperazine as a pharmacophore for protein lysine methyltransferase G9a inhibitors: reducing cytotoxicity by structural simplification

Chaetocin (1), a structurally complex epidithiodiketopiperazine (ETP) alkaloid produced by Chaetomium minutum, is a potent inhibitor of protein lysine methyltransferase G9a, which plays important roles in many biological processes. Here we present our synthetic investigations to identify a simple prototype G9a inhibitor structure based on structure-activity relationship (SAR) studies on chaetocin derivatives. The simple derivative PS-ETP-1 (14) was found to be a potent G9a inhibitor with greatly reduced cytotoxicity.

Total syntheses of (-)-fructigenine A and (-)-5-N-acetylardeemin

The first total synthesis of (-)-fructigenine A and a novel approach to (-)-5-N-acetylardeemin through a common imine intermediate (+)-3 are described. The key steps include highly enantioselective preparation of (+)-3 via domino olefination/isomerization/Claisen rearrangement (OIC) of 5, reductive cyclization (RC), and regioselective oxidation of (-)-4 and a novel assembly of the pyrazino ring of these alkaloids via Ugi three-component reaction/cyclization of (+)-3 with the corresponding amino acid and isonitrile.

Brief total synthesis of the cell cycle inhibitor tryprostatin B and related preparation of its alanine analogue

Tryprostatin B was synthesized in 32% overall yield from the readily available dipeptide anhydride cyclo-(l-Trp-l-Pro). Its tandem C-3 prenylation/cyclization gave the corresponding pentacyclic pyrroloindole systems bearing a prenyl group at the indole C-3 position. These compounds were then submitted to acid-catalyzed opening of the newly formed ring, with concomitant migration of the prenyl group to the indole C-2 position. The alanine analogue of tryprostatin B was also prepared using a similar sequence. The successful implementation of this strategy strengthens the case for a biosynthetic route for the tryprostatins along similar lines.