A formal synthesis of the antitumor diterpenoid paclitaxel (Taxol) is described. The ABC ring of paclitaxel, synthesized starting from 1,3-cyclohexanedione and tri-O-acetyl-d-glucal by SmI2-mediated cyclization as the key transformation, was successfully converted to Takahashi's tetracyclic oxetane intermediate. A double Chugaev reaction was employed for introduction of the strained bridgehead olefin, and stereoselective formation of the oxetane ring afforded the known synthetic intermediate, completing the formal synthesis of paclitaxel.

A convergent synthesis of the ABC ring of antitumor natural product paclitaxel (Taxol) is described. SmI2-mediated reductive cyclization of an allylic benzoate possessing an aldehyde function, synthesized from tri-O-acetyl-d-glucal and 1,3-cyclohexanedione, smoothly afforded the highly strained 6-8-6 tricarbocyclic structure in 66% yield.

Hydrogen peroxide (H2O2) is known to be generated in Photosystem II (PSII) via enzymatic and non-enzymatic pathways. Detection of H2O2 by different spectroscopic techniques has been explored, however its sensitive detection has always been a challenge in photosynthetic research. During the recent past, fluorescence probes such as Amplex Red (AR) has been used but is known to either lack specificity or limitation with respect to the minimum detection limit of H2O2. We have employed an electrochemical biosensor for real time monitoring of H2O2 generation at the level of sub-cellular organelles. The electrochemical biosensor comprises of counter electrode and working electrodes. The counter electrode is a platinum plate, while the working electrode is a mediator based catalytic amperometric biosensor device developed by the coating of a carbon electrode with osmium-horseradish peroxidase which acts as H2O2 detection sensor. In the current study, generation and kinetic behavior of H2O2 in PSII membranes have been studied under light illumination. Electrochemical detection of H2O2 using the catalytic amperometric biosensor device is claimed to serve as a promising technique for detection of H2O2 in photosynthetic cells and subcellular structures including PSII or thylakoid membranes. It can also provide a precise information on qualitative determination of H2O2 and thus can be widely used in photosynthetic research.

All living organisms bear its defense mechanism. Immune cells during invasion by foreign body undergoes phagocytosis during which monocyte and neutrophil produces reactive oxygen species (ROS). The ROS generated in animal cells are known to be involved in several diseases and ailments, when generated in excess. Therefore, if the ROS generated in cells can be measured and analyzed precisely, it can be employed in immune function evaluation and disease detection. The aim of the current study is to introduce our newly developed chip-type biosensor device with high specificity and sensitivity. It comprises of counter electrode and working electrodes I and II. The counter electrode is a platinum plate while the working electrodes I and II are platinum microelectrode and osmium-horseradish peroxidase modified gold electrode, respectively which acts as oxygen and hydrogen peroxide (H 2 O 2 ) detection sensors. Simultaneous measurement of oxygen consumption and H 2 O 2 generation were measured in animal cells under the effect of exogenous addition of differentiation inducer, phorbol 12-myristate 13-acetate. The results obtained showed considerable changes in reduction currents in the absence and presence of inducer. Our newly developed chip-type biosensor device is claimed to be a useful tool for real-time monitoring of the respiratory activity and precise detection of H 2 O 2 in cells. It can thus be widely applied in biomedical research and in clinical trials being an advancement over other H 2 O 2 detection techniques.

<p>Bioconjugation reactions are a fundamental synthetic method for generating artificial peptides and proteins. Despite the potentially superior properties of bioconjugates at hydrophobic amino acid residues compared with those at hydrophilic amino acids, methods to target hydrophobic amino acids with moderate reactivity under mild and metal-free conditions are limited. Here we report the first electrochemically-promoted tryptophan (Trp)-selective bioconjugation of peptides and proteins in neutral aqueous media. The unique electrochemical cooperation of two radicals, keto-ABNO and 4-oxo-TEMPO, was critical to suppress both anodic overoxidation of the products and cross reactivity. Systematic cyclic voltammetry analysis suggested that these two radicals, containing similar redox potentials but contrasting steric demands, had distinct electrochemical roles (reactant and electrochemical mediator). This new protocol will be an important advance toward clean and scalable syntheses of chemically modified biologics.</p>