Convergent Synthesis of Complex Diketopiperazines Derived from Pipecolic Acid Scaffolds and Parallel Screening against GPCR Targets

Determination of the active stereoisomer of the MEP pathway-targeting antimalarial agent MMV008138, and initial structure-activity studies

Compounds that target isoprenoid biosynthesis in Plasmodium falciparum could be a welcome addition to malaria chemotherapy, since the methylerythritol phosphate (MEP) pathway used by the parasite is not present in humans. We previously reported that MMV008138 targets the apicoplast of P. falciparum and that its target in the MEP pathway differs from that of Fosmidomycin. In this Letter, we determine that the active stereoisomer of MMV008138 is 4a, which is (1R,3S)-configured. 2',4'-Disubstitution of the D ring was also found to be crucial for inhibition of the parasite growth. Limited variation of the C3-carboxylic acid substituent was carried out, and methylamide derivative 8a was found to be more potent than 4a; other amides, acylhydrazines, and esters were less potent. Finally, lead compounds 4a, 4e, 4f, 4h, 8a, and 8e did not inhibit growth of Escherichia coli, suggesting that protozoan-selective inhibition of the MEP pathway of P. falciparum can be achieved.

Synthesis of azaphilone-based chemical libraries

The synthesis of azaphilone scaffolds that have been further diversified by cross coupling acylation and amine addition is reported. Methodology development also led to novel modifications including C5 acetoxylation and condensations producing isoquinolin-6(7H) structures. Overall, the library synthesis afforded three azaphilone sublibraries, including vinylogous pyridones which project diversity elements in four sectors of the azaphilone core.

Synthesis of reblastatin, autolytimycin, and non-benzoquinone analogues: potent inhibitors of heat shock protein 90

A full account of an asymmetric synthesis of reblastatin (1) and the first total synthesis of autolytimycin (2) and related structural compounds is described. The syntheses expand the utility of a highly regio- and diastereoselective hydrometalation aldehyde addition sequence to assemble the fully functionalized ansa chain of the natural products. Also documented is an intramolecular copper-mediated amidation reaction to close the 19-membered macrolactams. The amidation reaction was also employed for the generation of structural derivatives (6-9) of phenolic ansamycins. Ansamycin natural products and selected structural analogues were evaluated in a competitive binding assay to breast cancer cell lysate and a cytotoxicity assay. Both reblastatin (1) and autolytimycin (2) were shown to bind the heat shock protein 90 with enhanced binding activity (approximately 25 nM) than 17-allylamino-17-demethoxygeldanamycin (17-AAG, 4), a geldanamycin (3) derivative currently under evaluation for treatment of cancer (approximately 100 nM).

Stereoselective cyclopropanation of serine- and threonine-derived oxazines to access new morpholine-based scaffolds

A general strategy for the synthesis of novel, orthogonally protected scaffolds based on the unique 2-oxa-5-azabicyclo[4.1.0]heptane structure is presented. The described reaction sequence takes advantage of easily available starting materials such as serine and threonine and leads to stereochemically dense structures in few, high-yielding synthetic steps. We show how the stereochemistry can be easily tuned by starting from different beta-hydroxy-alpha-amino acids and also by means of a transition metal-catalyzed cyclopropanation step. The compounds find application as constrained templates for the construction of geometrically diversified libraries of compounds.

Biaryl phosphane ligands in palladium-catalyzed amination

Palladium-catalyzed amination reactions of aryl halides have undergone rapid development in the last 12 years, largely driven by the implementation of new classes of ligands. Biaryl phosphanes have proven to provide especially active catalysts in this context. This Review discusses the application of these catalysts in C-N cross-coupling reactions in the synthesis of heterocycles and pharmaceuticals, in materials science, and in natural product synthesis.

Skeletal Diversity through Radical Cyclization of Tetrahydropyridine Scaffolds

Suitably functionalized tetrahydropyridines (methyl pipecolates) have been used as conformationally biased templates for radical cyclizations to access benzoisoquinuclidines and linearly fused indenopiperidines. Variation of skeletal types is determined by location of a radical-initiating element.

Stereochemical and Skeletal Diversity Employing Pipecolate Ester Scaffolds

[structure: see text] The stereocontrolled synthesis of pyridooxazinones by Mg(OTf)2-promoted epoxide ring-opening with use of chiral pipecolates as nucleophiles is described. Pyridooxazinone products derived from azido-epoxides can be further rearranged to seven-membered pyridodiazepinones by azide reduction. The sequence of functional group interconversions generates diversity through topological and stereochemical variation.