Lithium (2,6-diisopropylphenyl)(trimethylsilyl)amide (2,6-iPr2C6H3N(SiMe3)Li) reacts with MCl4 (M = Zr, Hf) in a 2:1 molar ratio to give [{2,6-iPr2C6H3N(SiMe3)}2MCl2] (1a, M = Zr; 1b, M = Hf) and with (C5Me5)MCl3 (1:1) to give [(C5Me5){2,6-iPr2C6H3N(SiMe3)}MCl2] (2a, M = Zr; 2b, M = Hf). Further reaction of the dichlorides (1a,b, 2a,b) with Me3SnF leads to the corresponding difluorides [{2,6-iPr2C6H3N(SiMe3)}2MF2] (3a, M = Zr; 3b, M = Hf) and [(C5Me5){2,6-iPr2C6H3N(SiMe3)}MF2] (4a, M = Zr; 4b, M = Hf). The compounds 1−4 were investigated as potential catalysts for the polymerization of olefins, in combination with methylaluminoxane (MAO). For the first time the catalytic activities, toward the polymerization of ethylene, of chlorides and the corresponding fluorides are compared under identical conditions. The solid-state structures of 1a,b, 2b, 3a, and 4a were determined by single-crystal X-ray diffraction.

A series of benzimidazole derivatives (1-20) was synthesized and evaluated for its in vitro antimicrobial, antitubercular and anticancer activities. Compound 10 was found to be the most active antibacterial agent. The compounds active in in vitro evaluation against M. tuberculosis were further assessed for their in vivo activity in mice and for their capacity to inhibit the vital mycobacterial enzymes viz., isocitrate lyase, pantothenate synthetase and chorismate mutase. The dose of the compounds in antitubercular evaluation that proved fatal and highly toxic to mice was 5.67 mg/kg while lethal dose varied from 1.82 mg/kg to 3.23 mg/kg body weight of the mice. A dose of 1.34 mg/kg was found to be safe for each of the compounds. All compounds inhibited the mycobacterial enzymes but to a lesser extent than streptomycin sulphate used as positive control. Compound 19, exhibiting inhibition of 67.56%, 53.45%, and 47.56% against isocitrate lyase, pantothenate synthetase and chorismate mutase, respectively is the most potent antitubercular compound among the synthesized benzimidazole derivatives. Further, compound 19 also emerged as a potent anticancer agent (IC 50 = 0.0013 mM) than 5-flourouracil against breast cancer cell line (MCF 7).

Microbial-catalyzed biotransformations have considerable potential for the generation of an enormous variety of structurally diversified organic compounds, especially natural products with complex structures like triterpenoids. They offer efficient and economical ways to produce semi-synthetic analogues and novel lead molecules. Microorganisms such as bacteria and fungi could catalyze chemo-, regio- and stereospecific hydroxylations of diverse triterpenoid substrates that are extremely difficult to produce by chemical routes. During recent years, considerable research has been performed on the microbial transformation of bioactive triterpenoids, in order to obtain biologically active molecules with diverse structures features. This article reviews the microbial modifications of tetranortriterpenoids, tetracyclic triterpenoids and pentacyclic triterpenoids.

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