In vitro study for antifungal compounds from Parinari curatellifolia (Chrysobalanaceae) and Terminalia sericea (Combretaceae)

Parinari curatellifolia (Chrysobalanaceae) and Terminalia sericea (Combretaceae) have been traditionally used in Southern Highlands of Tanzania for treatment of various infectious disorders. The present study aimed to evaluate antifungal activity of the isolated  compounds from Parinari curatellifolia and Terminalia sericea plant species. The ethyl acetate extract of the root barks from Parinari curatellifolia and Terminalia sericea were fractionated using column chromatography. The structures of compounds were established using both 1D and 2D-NMR spectroscopic techniques while antifungal activities of the fractions and isolated compounds were evaluated using broth microdilution assay against Candida albicans, Cryptococcus neoformans and Aspergillus niger species. Two known compounds toddalolactone (1) and 10-hydroxy-13-methoxy-9- methyl-15-oxo-20-norkaur-16-en-18-oic acid -lactone (2) from P. curatellifolia and two compounds Sericic acid (3) and sericoside (4) from T. sericea were isolated and their structures identified and confirmed by spectral data obtained and from the literatures. Strong antifungal activity was shown by Sericic acid (3) with MIC value of0.07 mg/ml against C. albicans and C. neoformans. Isolation of toddalolactone (1) from Parinari curatellifolia as well as the antifungal activity of Sericic acid (3) from Terminalia sericea is being reported for the first time. Bioactivity of these compounds support traditional use of the studied plants. Keywords: Sericic acid, toddalolactone, fungi, antifungal, Parinari curatellifolia, Terminalia sericea

Experimental and Theoretical Mechanistic Investigation of the Iridium-Catalyzed Dehydrogenative Decarbonylation of Primary Alcohols

The mechanism for the iridium–BINAP catalyzed dehydrogenative decarbonylation of primary alcohols with the liberation of molecular hydrogen and carbon monoxide was studied experimentally and computationally. The reaction takes place by tandem catalysis through two catalytic cycles involving dehydrogenation of the alcohol and decarbonylation of the resulting aldehyde. The square planar complex IrCl­(CO)­(<i>rac</i>-BINAP) was isolated from the reaction between [Ir­(cod)­Cl]₂, <i>rac</i>-BINAP, and benzyl alcohol. The complex was catalytically active and applied in the study of the individual steps in the catalytic cycles. One carbon monoxide ligand was shown to remain coordinated to iridium throughout the reaction, and release of carbon monoxide was suggested to occur from a dicarbonyl complex. IrH₂Cl­(CO)­(<i>rac</i>-BINAP) was also synthesized and detected in the dehydrogenation of benzyl alcohol. In the same experiment, IrHCl₂(CO)­(<i>rac</i>-BINAP) was detected from the release of HCl in the dehydrogenation and subsequent reaction with IrCl­(CO)­(<i>rac</i>-BINAP). This indicated a substitution of chloride with the alcohol to form a square planar iridium alkoxo complex that could undergo a β-hydride elimination. A KIE of 1.0 was determined for the decarbonylation and 1.42 for the overall reaction. Electron rich benzyl alcohols were converted faster than electron poor alcohols, but no electronic effect was found when comparing aldehydes of different electronic character. The lack of electronic and kinetic isotope effects implies a rate-determining phosphine dissociation for the decarbonylation of aldehydes

Evolution and Prospects of the Asymmetric Hydrogenation of Unfunctionalized Olefins

The catalytic enantioselective hydrogenation of prochiral olefins is a key reaction in asymmetric synthesis. Its relevance applies to both industry and academia as an inherently direct and sustainable strategy to induce chirality. Here we briefly recount the early breakthroughs concerning the asymmetric hydrogenation of largely unfunctionalized olefins, from the first reports to the advent of chiral Crabtree-like catalysts. The mechanism and its implications on the enantioselectivity are shortly discussed. The main focus of this Perspective lies on the more recent advances in the field, such as the latest developed classes of ligands and the opportunity to employ more Earth-abundant metals. Therefore, separate sections consider iridium N,P-, NHC-, P,S-, and O,P catalysts, and rhodium, palladium, cobalt, and iron catalysts. Finally, the remaining unsolved challenges are examined, and the potential directions of forthcoming research are outlined

Development of iridium-catalyzed asymmetric hydrogenation : New catalysts, new substrate scope

A review. The asym. hydrogenation of olefins is a tremendously powerful tool used to synthesize chiral mols. The field was pioneered using rhodium- and ruthenium- based catalysts; however, catalysts based on both of these metals suffer from limitations, such as the need for directing substituents near or even adjacent to the olefin. Iridium-based catalysts do not suffer from this flaw and can thus hydrogenate a wide variety of olefins, including some tetra substituted ones. It is also possible for iridium-based catalysts to hydrogenate hetero-π bonds such as those found in heteroarom. rings. This review summarizes the contributions made to this field by the authors in the past few years. [on SciFinder(R)

Iridium catalysis : application of asymmetric reductive hydrogenation

Iridium, despite being one of the least abundant transition metals, has found several uses. N,P-ligated iridium catalysts are used to perform many highly selective reactions. These methodologies have been developed extensively over the past 15 years. More recently, the application of iridium N,P catalysts in asymmetric hydrogenation has been a focus of research to find novel applications and to expand on their current synthetic utility. The aim of this perspective is to highlight the advances made by the Andersson group.AuthorCount:2;</p