Donor-acceptor-substituted cyclopropane derivatives and their application in organic synthesis.

Occurrence, Biogenesis, and Synthesis of Biologically Active Carbazole Alkaloids

BINOL: A Versatile Chiral Reagent

Claisen rearrangement over the past nine decades.

C2-Symmetric Chiral Bis(Oxazoline) Ligands in Asymmetric Catalysis

Infecting one-third of the world’s inhabitants, Mycobacterium tuberculosis (MTB) is deemed a serious public health concern. Failure to follow the current regimen along with the HIV pandemic have led to the emergence of multiple drug-resistant tuberculosis (MDR-TB) strains. The pursuit of more efficacious drugs and prophylaxis is warranted. Findings of some naturally occurring carbazole alkaloids (Figure 1), exhibiting antituberculosis activity, have prompted us to explore further carbazole derivatives for structure–activity relationships. Clausine K or clauszoline J, a natural product isolated independently from several sources, was found to have weak antituberculosis activity (MIC of 100 mgmL 1 against the H37Ra strain). Ma et al. isolated micromeline from the stem bark of Micromelum hirsutum along with some known carbazole alkaloids, and found the MIC to be 31.5 mgmL 1 against M. tuberculosis H37Rv (selectivity index >3). [8] Based on these findings, we screened a series of carbazole alkaloids and derivatives for their in vitro anti-TB activity to find out whether the carbazole framework represents a novel antituberculosis scaffold. The intention of the present study was to identify potent anti-TB active carbazoles and to establish preliminary structure–activity relationships (SAR). Compounds 4a–i were purchased from Sigma Aldrich; 4 j–v and 8–15 were prepared using either the iron-mediated or the palladium-catalyzed approach previously developed by our group (Schemes 1 and 2, Table 1). An electrophilic aromatic substitution of the tricarbonyliron-cyclohexadienylium salts 1 and the arylamines 2 affords functionalized tricarbonyliron complexes 3. The oxidative cyclization of the tricarbonyliron complexes 3 furnishes substituted carbazole derivatives 4. In another approach, the palladium(0)-catalyzed amination of aryl

Synthesis and activity of carbazole derivatives against Mycobacterium tuberculosis

The Catalytic Enantioselective Claisen Rearrangement of an Allyl Vinyl Ether

A series of carbazole derivatives with promising pharmacological properties has been prepared using either an iron-mediated or a palladium-catalyzed synthetic approach. The carbazole alkaloids carbazoquinocin C, carbazomadurin A and B, epocarbazolin A and B, neocarazostatin B, and carquinostatin A are antioxidants acting as free-radical scavengers. Thus, they represent potential lead compounds for the development of novel drugs against diseases initiated by oxygen-derived free radicals. Initiated by the first naturally occurring carbazole alkaloids with antituberculosis (anti-TB) activity, clausine K and micromeline, a study on the structure–activity relationships for anti-TB-active carbazole derivatives has been carried out. The 6-oxygenated carbazoles glycozoline and glycozolinine show antibiotic activity towards several microorganisms. The 7-oxygenated carbazole siamenol exhibits anti-HIV activity.

Transition metals in organic synthesis - Part 83#: Synthesis and pharmacological potential of carbazoles

Pd(II) caught in the act: The diaryl Pd(II) intermediate of a Pd(II)-catalyzed oxidative biaryl bond formation proceeding via a double C-H bond activation has been isolated and fully characterized, including an X-ray crystal structure analysis. Stabilization due to chelation by adjacent pivaloyloxy and acetyl groups has allowed the isolation of this long-sought crucial intermediate. On gentle warming, the complex is transformed into a carbazole product, and the catalytically active Pd(II) species is regenerated by oxidation with Cu(II).

Regina Czerwonka

Papers

Synthesis and activity of carbazole derivatives against Mycobacterium tuberculosis

The Catalytic Enantioselective Claisen Rearrangement of an Allyl Vinyl Ether

Transition metals in organic synthesis - Part 83#: Synthesis and pharmacological potential of carbazoles

Snapshot of the Palladium(II)-Catalyzed Oxidative Biaryl Bond Formation by X-ray Analysis of the Intermediate Diaryl Palladium(II) Complex†

The Catalytic Enantioselective Claisen Rearrangement of an Allyl Vinyl Ether.