Physical Organic Chemistry

Hine, Jack

doi:10.1021/cen-v038n019.p101

Cited by 42 publications

(50 citation statements)

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“…It is well known that the most thermodynamically stable isomer is not always the initial product of a chemical reaction and that less stable isomers may be formed first (26), which is the case for the KDNase Sm-catalyzed hydrolysis. KDNase Smor sialidase-catalyzed reversible hydrolysis is represented schematically in Fig.…”

Section: Effects Of 23-didehydro-23-dideoxy Derivatives Of Sialic Amentioning

confidence: 99%

Catalysis by a New Sialidase, Deaminoneuraminic Acid Residue-cleaving Enzyme (KDNase Sm), Initially Forms a Less Stable α-Anomer of 3-Deoxy-D-glycero-D-galacto-nonulosonic Acid and Is Strongly Inhibited by the Transition State Analogue, 2-Deoxy-2,3-didehydro-D-glycero-D-galacto-2-nonulopyranosonic Acid, but Not by 2-Deoxy-2,3-didehydro-N-acetylneuraminic Acid

Terada

Kitajima

Inoue

et al. 1997

Journal of Biological Chemistry

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Deaminoneuraminic acid residue-cleaving enzyme (KDNase Sm) is a new sialidase that has been induced and purified from Sphingobacterium multivorum. Catalysis by this new sialidase has been studied by enzyme kinetics and 1 H NMR spectroscopy. V max /K m values determined for synthetic and natural substrates of KDNase Sm reveal that 4-methylumbelliferyl-KDN (KDN␣2MeUmb, V max /K m ‫؍‬ 0.033 min ؊1 ) is the best substrate for this sialidase, presumably because of its good leaving group properties. The transition state analogue, 2,3-didehydro-2,3-dideoxy-D-galacto-D-glycero-nonulosonic acid, is a strong competitive inhibitor of KDNase Sm (K i ‫؍‬ 7.7 M versus K m ‫؍‬ 42 M for KDN␣2MeUmb). 2-Deoxy-2,3-didehydro-N-acetylneuraminic acid and 2-deoxy-2,3-didehydro-N-glycolylneuraminic acid are known to be strong competitive inhibitors for bacterial sialidases such as Arthrobacter ureafaciens sialidase; however, KDNase Sm activity is not significantly inhibited by these compounds. This observation suggests that the hydroxyl group at C-5 is important for recognition of the inhibitor by the enzyme.Reversible addition of water molecule (or hydroxide ion) to the reactive sialosyl cation, presumably formed at the catalytic site of KDNase Sm, eventually gives rise to two different adducts, the ␣-and ␤-anomers of free 3-deoxy-D-glycero-D-galacto-nonulosonic acid. 1 H NMR spectroscopic studies clearly demonstrate that the thermodynamically less stable ␣-form is preferentially formed as the first product of the cleavage reaction and that isomerization rapidly follows, leading to an equilibrium mixture of the two isomers, the ␤-isomer being the major species at equilibrium. Therefore, we propose that KDNase Sm catalysis proceeds via a mechanism common to the known exosialidases, but the recognition of the substituent at C-5 by the enzyme differs.

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Section: Effects Of 23-didehydro-23-dideoxy Derivatives Of Sialic Amentioning

confidence: 99%

Catalysis by a New Sialidase, Deaminoneuraminic Acid Residue-cleaving Enzyme (KDNase Sm), Initially Forms a Less Stable α-Anomer of 3-Deoxy-D-glycero-D-galacto-nonulosonic Acid and Is Strongly Inhibited by the Transition State Analogue, 2-Deoxy-2,3-didehydro-D-glycero-D-galacto-2-nonulopyranosonic Acid, but Not by 2-Deoxy-2,3-didehydro-N-acetylneuraminic Acid

Terada

Kitajima

Inoue

et al. 1997

Journal of Biological Chemistry

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“…The constants p and pr represent the sensitivity of the reaction to polar and resonance effects, respectively. The o+ substituent constant describes the interaction of the substituent with a carbonium ion, on represents the polar effect of the substituent (38), and (o+ -on) represents the ability of the substituent to donate electrons by resonance. The resonance effect of the substituent (o+ -on) decreases in the order methoxy > methyl > chloro.…”

Section: -7mentioning

confidence: 99%

Isotope effects in nucleophilic substitution reactions. IV. The effect of changing a substituent at the α carbon on the structure of S_N2 transition states

Westaway¹,

Waszczylo²

1982

Can. J. Chem.

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Kinetic studies, secondary α-deuterium kinetic isotope effects, primary chlorine kinetic isotope effects (1), Hammett ρ values determined by changing the substituent in the nucleophile, and activation parameters have been used to determine the detailed (relative) structures of the transition states for the SN2 reactions between para-substituted benzyl chlorides and thiophenoxide ion. A rationale for the U-shaped Hammett ρ plots observed when para-substituted benzyl compounds react with negatively charged nucleophiles is also presented.

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“…In fact we are dealing with a transition-state like situation of bond formation between the amino function and the pyridinium ring, 3. The situation can be compared to neighbouring group participation by nitrogen in solvolysis reactions, where the lone pair of nitrogen interacts with an incipient carbocation [6]. This result fits into the reactivity pattern of compound lc .…”

Section: Discussionmentioning

confidence: 69%