The mechanism of rearrangement of chorismic acid and related compounds

Unified synthesis of caged Garcinia natural products based on a site-selective Claisen/Diels–Alder/Claisen rearrangement

“…This argument implies the development of partial charges during the transition state of the Claisen rearrangement. Such a polar transition state has been supported by both computational studies (27,28) and kinetic isotope effects, showing that the O-C ␣ bond is more broken (50-60%) than the C-C ␥ bond is formed (10-20%) (29). Polar solvents offset the development of such charges (30,31), which are further stabilized by the presence of the geminal dimethyl unit at the C18 carbon center.…”

Nonstatistical 13C Distribution during Carbon Transfer from Glucose to Ethanol during Fermentation Is Determined by the Catabolic Pathway Exploited

“…The mechanism of 6-phosphogluconate dehydrogenase has been elucidated (31, 32) and a 13 C KIE ϭ 1.0209 Ϯ 0.0005 has been determined for the C-1 G during decarboxylation by the enzyme from the yeast Candida utilis (31). Although no data are available for the C-2 G position, a KIE of a similar magnitude is probable (33), so an app KIE Ϸ1.006 is compatible with the proposed mechanism. It should be noted that, because reactions are not occurring under V max /K m conditions, values of app KIE obtained in vivo can be expected to be lower than values of KIE obtained under in vitro conditions.…”

Exploring the active site of chorismate mutase by combinatorial mutagenesis and selection: the importance of electrostatic catalysis.

“…In the uncatalyzed reaction, C-O bond cleavage substantially precedes the formation of the new C-C bond resulting in a dipolar transition state (10)(11)(12)39). It was proposed (7,9) that the developing positive charge on the cyclohexadienyl ring may be stabilized by negative polarization of the bottom of the active site through the anionic carboxylate of Glu-78 in the BsCM-catalyzed rearrangement (Figs.…”

“…Solvent effects show that the transition state for the uncatalyzed rearrangement is polar in character (10,11) and kinetic isotope effects indicate that C-O bond cleavage precedes C-C bond formation (11,12). Residues Arg-90 and Glu-78 in BsCM are positioned to complement a putative C-O dipole electrostatically.…”