Hynninen, Paavo H.; Leppaekases, Tuomo S.; Mesilaakso, Markku published the artcile< The enolate anions of chlorophylls a and b as ambident nucleophiles in oxidations with (-)- or (+)-(10-camphorsulfonyl)oxaziridine. Synthesis of 132(S/R)-hydroxychlorophylls a and b>, Application In Synthesis of 104322-63-6, the main research area is chlorophyll enolate stereoselective hydroxylation camphorsulfonyloxaziridine mechanism; ambident nucleophile chlorophyll enolate; hydroxychlorophyll diastereoselective preparation carbon NMR.
The enolate anions of chlorophylls (Chl) are ambident nucleophiles that are of considerable organic chem. interest in relation to the theory of electron delocalization (aromaticity) and charge-transfer in large conjugated π-systems, as well as for their chem. reactivity. Under deaerated conditions, the (-)- and (+)-enantiomers of (10-camphorsulfonyl)oxaziridine (CSOAI) are effective oxidants for the enolate anions of Chl a and Chl b, when 1,8-diazabicyclo[5.4.0]undec-7-ene (DBU) serves as a base. The use of these sterically hindered reagents to hydroxylate Chl a and Chl b is described for the first time. The total yield of 132(S/R)-HO-Chl a was 71 and 90% for the oxidations of Chl a with (-)-CSOAI and (+)-CSOAI, resp. Chl b, however, behaved clearly differently from Chl a. The total yield of 132(S/R)-HO-Chl b was 40% in the oxidation with (-)-CSOAI and 60% in the reaction with (+)-CSOAI. A competing side-reaction, which resulted in the 152-Me, 173-phytyl ester of Mg-151(S/R)-unstable rhodin, was found to lower the yields of the desired main products. The formation of the side-products was largely avoided and the yield of 132(S/R)-HO-Chl b was improved by increasing the volume of hexane and using phosphate buffer in the first step of the work-up. With (-)-CSOAI, a 94% diastereomeric excess (de) was achieved for 132(R)-HO-Chl a, whereas the de for 132(R)-HO-Chl b was 66%. With (+)-CSOAI, the de was 10% for 132(R)-HO-Chl a and 8% for 132(R)-HO-Chl b. The results were interpreted in terms of a nucleophilic reaction mechanism, kinetically controlled by steric hindrance, originating on the one hand in the 17-propionate phytyl ester side-chain, protruding over the isocyclic ring E of the Chl enolate ion, and however, in the bulky camphorsulfonyl unit of CSOAI. Possible reasons for the different results from the Chl b oxidations as compared with those of the Chl a oxidations are discussed. Comparison of the differences in the NMR δC-values between 132(S)- and 132(R)-HO-Chl a as well as those between 132(S)- and 132(R)-HO-Chl b, indicated that the change of stereochem. configuration at C-132 induces only slight differences in the δC-values. Of special interest are the δC-values of C-132, which are at ∼91 ppm for the a- and b-series diastereomers. This C is deshielded by ∼25 ppm relative to the C-132 of 132(R)-Chl a (δC = 65.5). Owing to this, 13C NMR spectroscopy is a good method to distinguish the 132-hydroxylated chlorophylls from the intact, naturally occurring chlorophylls.
Tetrahedron published new progress about Hydroxylation, stereoselective. 104322-63-6 belongs to class isothiazole, and the molecular formula is C10H15NO3S, Application In Synthesis of 104322-63-6.
Referemce:
Isothiazole – Wikipedia,
Isothiazole – ScienceDirect.com