22532-51-0Relevant articles and documents
Regioselective nitrile addition to hindered tricarbonylcyclohexadienyliumiron complexes and spirolactone formation
Ong, Chi Wi,Chien, Chen Jeng
, p. 241 - 243 (1993)
By using a large excess of trimethylsilyl cyanide and a short reaction time, trimethyl isocyanide in sufficient amount is generated and added regioselectively at the C-1 terminus of the tricarbonyl cyclohexadienylium species 1, irrespective of steric hindrance and its α-proton acidity. Formation of the aromatic and trienyl complex is suppressed. Upon saponification or hydrolysis, addition product 2c is converted into the synthetically useful spirolactone 6. For the reaction mechanism, formation of phosphorus pentafluoride, trimethylsilyl fluoride, and free cyanide during the reaction between hexafluorophosphate anion and trimethylsilyl cyanide is suggested.
A deprotection procedure using SO3H silica gel to remove non-silyl protecting groups
Karaki, Fumika,Kuwada, Miki,Tajiri, Saki,Kanda, Misaki,Yanai, Mari,Kamimura, Mitsuhiro,Itoh, Kennosuke,Fujii, Hideaki
supporting information, p. 212 - 220 (2019/05/06)
Protecting groups are indispensable in organic synthesis and there is a great need for a variety of deprotection methods. Here, we investigated the scope of the application of a deprotection procedure using SO3H silica gel, which we have previously reported as a desilylation procedure. Under these conditions, -OMOM, -OSEM, -OTHP, and -OAc groups and dimethyl acetal were cleaved. Pivaloyloxy, benzyloxy and methoxy carbonyl groups remained intact and selective deprotection of TBS groups in the presence of other protecting groups was accomplished. We succeeded in cleaving an acetyl group on a secondary alcohol in a highly polar nortropine derivative. Our findings here provide another deprotection option and would be helpful in the synthesis of multifunctional compounds.
Structural and catalytic characterization of a fungal baeyer-villiger monooxygenase
Ferroni, Felix Martin,Tolmie, Carmien,Smit, Martha Sophia,Opperman, Diederik Johannes
, (2017/03/27)
Baeyer-Villiger monooxygenases (BVMOs) are biocatalysts that convert ketones to esters. Due to their high regio-, stereo- and enantioselectivity and ability to catalyse these reactions under mild conditions, they have gained interest as alternatives to chemical Baeyer-Villiger catalysts. Despite their widespread occurrence within the fungal kingdom, most of the currently characterized BVMOs are from bacterial origin. Here we report the catalytic and structural characterization of BVMOAFL838 from Aspergillus flavus. BVMOAFL838 converts linear and aryl ketones with high regioselectivity. Steady-state kinetics revealed BVMOAFL838 to show significant substrate inhibition with phenylacetone, which was more pronounced at low pH, enzyme and buffer concentrations. Para substitutions on the phenyl group significantly improved substrate affinity and increased turnover frequencies. Steady-state kinetics revealed BVMOAFL838 to preferentially oxidize aliphatic ketones and aryl ketones when the phenyl group are separated by at least two carbons from the carbonyl group. The X-ray crystal structure, the first of a fungal BVMO, was determined at 1.9 A and revealed the typical overall fold seen in type I bacterial BVMOs. The active site Arg and Asp are conserved, with the Arg found in the ginh position. Similar to phenylacetone monooxygenase (PAMO), a two residue insert relative to cyclohexanone monooxygenase (CHMO) forms a bulge within the active site. Approximately half of the gvariableh loop is folded into a short ?-helix and covers part of the active site entry channel in the non-NADPH bound structure. This study adds to the current efforts to rationalize the substrate scope of BVMOs through comparative catalytic and structural investigation of different BVMOs.
