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2,3-Dichloro-5,6-dicyano-1,4-benzoquinone (or DDQ) is the chemical reagent with formula C 6 Cl 2 (CN) 2 O 2. This oxidant is useful for the dehydrogenation of alcohols, [3] phenols, [4] and steroid ketones. [5] DDQ decomposes in water, but is stable in aqueous mineral acid. [6]
(1) Fmoc-protected amino group, (2) benzyl ester protected carboxyl group and (3) tert-butyl ether protected phenolic hydroxyl group of Tyrosine. Orthogonal protection is a strategy allowing the specific deprotection of one protective group in a multiply-protected structure.
To a stirred solution of p-(3-hydroxypropyl)phenol (152 mg, 1 mmol) and pyridine (0.3 mL) in acetonitrile (10 mL) at 0° was added a solution of IBTA (430 mg, 1 mmol) in acetonitrile (2 mL). The mixture was stirred at room temperature for 10 minutes, diluted with water, and extracted with diethyl ether (3 × 10 mL).
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[5] [6] Selective cleavage of the N-Boc group in the presence of other protecting groups is possible when using AlCl 3. Sequential treatment with trimethylsilyl iodide then methanol can also be used for Boc deprotection, [7] [8] especially where other deprotection methods are too harsh for the substrate. [9]
Typically, selective cleavage of a PMB ether in the presence of a benzyl ether uses strong stoichiometric oxidants such as 2,3-dichloro-5,6-dicyano-1,4-benzoquinone (DDQ) or ceric ammonium nitrate (CAN). PMB ethers are far more susceptible to oxidation than benzyl ethers since they are more electron-rich.
Completing the cyclooctane ring required 3 more carbon atoms that were supplied by a C2 fragment in an aldol addition and a Grignard C1 fragment (scheme 2).A Mukaiyama aldol addition (magnesium bromide / toluene) took place between aldehyde 7 and ketene silyl acetal 8 with 71% stereoselectivity to alcohol 9 which was protected as the TBS ether 10 (TBSOTf, 2,6-lutidine).
20% piperidine in DMF (Fmoc group has an approximate half life of 6 seconds in this solution) [8] 5% piperazine, 1% DBU and 1% formic acid in DMF. This method avoids the use of strictly controlled piperidine. [9] No side product was observed for a peptide with 9 residues synthesized with this method. [10]