2 research outputs found
Mild and Regioselective Pd(OAc)<sub>2</sub>‑Catalyzed C–H Arylation of Tryptophans by [ArN<sub>2</sub>]X, Promoted by Tosic Acid
A regioselective
Pd-mediated C–H bond arylation methodology
for tryptophans, utilizing stable aryldiazonium salts, affords C2-arylated
tryptophan derivatives, in several cases quantitatively. The reactions
proceed in air, without base, and at room temperature in EtOAc. The
synthetic methodology has been evaluated and compared against other
tryptophan derivative arylation methods using the CHEM21 green chemistry
toolkit. The behavior of the Pd catalyst species has been probed in
preliminary mechanistic studies, which indicate that the reaction
is operating homogeneously, although Pd nanoparticles are formed during
substrate turnover. The effects of these higher order Pd species on
catalysis, under the reaction conditions examined, appear to be minimal:
e.g., acting as a Pd reservoir in the latter stages of substrate turnover
or as a moribund form (derived from catalyst deactivation). We have
determined that TsOH shortens the induction period observed when [ArN<sub>2</sub>]ÂBF<sub>4</sub> salts are employed with PdÂ(OAc)<sub>2</sub>. PdÂ(OTs)<sub>2</sub>(MeCN)<sub>2</sub> was found to be a superior
precatalyst (confirmed by kinetic studies) in comparison to PdÂ(OAc)<sub>2</sub>
British Society of Gastroenterology guidelines on sedation in gastrointestinal endoscopy
Over 2.5 million gastrointestinal endoscopic procedures are carried out in the United Kingdom (UK) every year. Procedures are carried out with local anaesthetic r with sedation. Sedation is commonly used for gastrointestinal endoscopy, but the type and amount of sedation administered is influenced by the complexity and nature of the procedure and patient factors. The elective and emergency nature of endoscopy procedures and local resources also have a significant impact on the delivery of sedation. In the UK, the vast majority of sedated procedures are carried out using benzodiazepines, with or without opiates, whereas deeper sedation using propofol or general anaesthetic requires the involvement of an anaesthetic team. Patients undergoing gastrointestinal endoscopy need to have good understanding of the options for sedation, including the option for no sedation and alternatives, balancing the intended aims of the procedure and reducing the risk of complications. These guidelines were commissioned by the British Society of Gastroenterology (BSG) Endoscopy Committee with input from major stakeholders, to provide a detailed update, incorporating recent advances in sedation for gastrointestinal endoscopy.This guideline covers aspects from pre-assessment of the elective 'well' patient to patients with significant comorbidity requiring emergency procedures. Types of sedation are discussed, procedure and room requirements and the recovery period, providing guidance to enhance safety and minimise complications. These guidelines are intended to inform practising clinicians and all staff involved in the delivery of gastrointestinal endoscopy with an expectation that this guideline will be revised in 5-years' time.</p