Mechanisms of photochemical reactions in solution. LV. Naphthalene-sensitized photoracemization of sulfoxides

Cooke, Robert S.; Hammond, George S.

doi:10.1021/ja01013a039

Cited by 32 publications

(23 citation statements)

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“…4‐Methoxyphenyl tert butyl sulfide was prepared by acid catalysed reaction of 4‐methoxythiophenol with t BuOH [55]. All the sulfoxides were prepared by reaction of the corresponding sulfides with sodium metaperiodate in aqueous ethanol solution [56] and exhibited physical properties identical to those reported in the literature [57–61]. The purity of all these compounds (> 99%) was checked by GC, GC‐MS and 1 H NMR.…”

Section: Methodsmentioning

confidence: 99%

Oxidation of aromatic sulfides by lignin peroxidase from Phanerochaete chrysosporium

Baciocchi

Gerini²,

Harvey

et al. 2000

European Journal of Biochemistry

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The reaction of H 2 O 2 with 4-substituted aryl alkyl sulfides (4-XC 6 H 4 SR), catalysed by lignin peroxidase (LiP) from Phanerochaete chrysosporium, leads to the formation of sulfoxides, accompanied by diaryl disulfides. The yields of sulfoxide are greater than 95% when X OMe, but decrease significantly as the electron donating power of the substituent decreases. No reaction is observed for X CN. The bulkiness of the R group has very little influence on the efficiency of the reaction, except for R t Bu. The reaction exhibits enantioselectivity (up to 62% enantiomeric excess with X Br, with preferential formation of the sulfoxide with S configuration). Enantioselectivity decreases with increasing electron density of the sulfide. Experiments in H 18 2 O show partial or no incorporation of the labelled oxygen into the sulfoxide, with the extent of incorporation decreasing as the ring substituents become more electron-withdrawing. On the basis of these results, it is suggested that LiP compound I (formed by reaction between the native enzyme and H 2 O 2 ), reacts with the sulfide to form a sulfide radical cation and LiP compound II. The radical cation is then converted to sulfoxide either by reaction with the medium or by a reaction with compound II, the competition between these two pathways depending on the stability of the radical cation.Keywords: lignin peroxidase; radical cation; oxygen transfer; aromatic sulfide; enantioselectivity. [24]. Very little is known about the substrate-binding site of LiP and the pathway of electron flux from substrate to oxidized heme. Based on the crystal structure of the resting state of the enzyme [25±27] and molecular dynamic simulations [28], a substrate access channel similar to the classical heme-edge/substrate interaction site found in HRP has been identified, which, whilst too small to enable access to polymeric lignin, could allow access to VA. The use of probes of the active site of LiP involving the mechanism-based inactivating agents (azide and phenylhydrazine) suggests that the meso edge may be more highly shielded in LiP than in HRP [29,30], which is surprising in the light of its high oxidative capacity, and contrasts with the situation with the more open sites of chloroperoxidase [31] or cytochrome P-450 [30]. Attempts to cocrystallize the enzyme with VA [25] or to locate the VA-binding site by NMR spectroscopy [32] have not been successful. More recently, studies using site-directed mutagenesis have pointed to a second, neẁ non-heme edge' long-range electron transfer site involving a redox-active tryptophan residue on the surface of LiP, which has been proposed to be relevant for the oxidation of VA and possibly lignin [33,34].Information about the enzyme active site and the binding mode of the substrate can be probed by examining the oxidation of different classes of compound. The oxidation of sulfides to sulfoxides catalyzed by cytochrome P-450, HRP, chloroperoxidase and lactoperoxidase has been thoroughly investigated [35±47] but no information is available ...

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Section: Methodsmentioning

confidence: 99%

Oxidation of aromatic sulfides by lignin peroxidase from Phanerochaete chrysosporium

Baciocchi

Gerini²,

Harvey

et al. 2000

European Journal of Biochemistry

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“…Alternatively, the small variance from 1.0 could result from the ratio of intersystem crossing It is interesting to note two correlations which these results present. The first is that the degree of concentration dependence of each sensitizer (as measured by the slopes of the plots in Figure 11 or by the values of in Table 4) follows the trend of decreasing reactivity in photoreduction and increasing triplet lifetime, as shown in (90). This quenching mechanism is very similar to the earlier proposed sensitizer self-quenching mechanism;…”

Section: Rearrangement and Reductionsupporting

confidence: 76%

Photochemical studies of some 2-cyclohexenones

Wampfler

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“…A number of rearrangements that qualify as exciplex isomerizations have been identified (34)(35)(36)(37)(38)(39). Importantly these photoisomerizations are induced by electron donor-…”

Section: Photosensitizat Ion Involving Exciplexesmentioning

confidence: 99%