Concise asymmetric total syntheses of (−)-nuciferol, (−)-nuciferal, and (−)-dihydrocurcumene via Rh(I)-catalyzed boronic acid addition

Taming secondary benzylic cations in catalytic asymmetric SN1 reactions

Benzylic stereogenic centers are ubiquitous in natural products and pharmaceuticals. A potentially general, though challenging, approach toward their selective creation would be asymmetric unimolecular nucleophilic substitution (SN1) reactions that proceed through highly reactive benzylic cations. We now report a broadly applicable solution to this problem by identifying chiral counteranions that pair with secondary benzylic cations to engage in catalytic asymmetric C-C, C-O, and C-N bond-forming reactions with excellent enantioselectivity. The critical cationic intermediate can be accessed from different precursors via Lewis- or Brønsted acid catalysis. Key to our strategy is the use of only weakly basic, confined counteranions that are posited to prolong the lifetime of the carbocation, thereby avoiding nonproductive deprotonation pathways to the corresponding styrene.

Diversity of actinomycete and their metabolites isolated from Howz Soltan Lake, Iran

Saline environments are largely unexplored sources of actinomycetes with the potential to produce biologically active secondary metabolites. A total of 34 actinomycete isolates from water, sediments and mostly rhizosphere (82%) were collected from different sites at Howz Soltan Lake in Iran. Based on phylogenetic analysis, the isolates belonged to the genera Streptomyces, Nocardia and Saccharomonospora. Cytotoxic assay revealed extract from isolate act9 as the most potent (19.716±5.72 µg/ml) against the MDA-MB-231 human breast cancer cell. Also, 38% of the isolates showed antimicrobial activity against some of the test microorganisms. The ethyl-acetate extract of isolate act18 showed the strongest antibacterial effect against Staphylococcus aureus and MRSA, and was further analyzed by GC/MS. Ar-tumerone (26.41%) and butyl isodecyl phthalate (21.77 %) were the main constituents detected in the extract. This is the first time Ar-tumerone is being detected in a prokaryote. Isolate act18 showed a high 16S rRNA sequence similarity to that of Streptomyces youssoufiensis DSM 41920. In addition, a number of the isolates produced different enzymes including lipase, amylase, protease, gelatinase, urease and lecithinase. Some of the isolates belonging to the genera Streptomyces and Nocardia exhibited plant growth promoting activity such as increased seed germination, stem length and the number of Echium leaves during the 20 days. Findings from this study indicated the diversity and biosynthetic potential of actinomycetes from saline environment.