Revisiting secondary interactions in neighboring group participation, exemplified by reactivity changes of iminylium intermediates

2017 ◽  
Vol 15 (6) ◽  
pp. 1381-1392 ◽  
Author(s):  
Yingtang Ning ◽  
Tomoya Fukuda ◽  
Hirotaka Ikeda ◽  
Yuko Otani ◽  
Masatoshi Kawahata ◽  
...  
Keyword(s):  
Reaction Pathway ◽  
Neighboring Group ◽  
Group Participation ◽  
Secondary Interactions ◽  
Neighboring Group Participation ◽  
Primary Interaction

In addition to the primary interaction with the nearest neighboring group, secondary interactions involving another neighboring group can also occur in principle, changing the reaction pathway.

scholarly journals An Epoxide Intermediate in Glycosidase Catalysis

2019 ◽  
Author(s):  
Lukasz F. Sobala ◽  
Gaetano Speciale ◽  
Sha Zhu ◽  
Lluís Raich ◽  
Natalia Sannikova ◽  
...  
Keyword(s):  
Transition State ◽  
Reaction Pathway ◽  
Reaction Coordinate ◽  
Glycoside Hydrolases ◽  
Glycoside Hydrolase Family ◽  
Neighboring Group ◽  
Group Participation ◽  
Enzymatic Mechanism ◽  
Key Species ◽  
Neighboring Group Participation

<div>Retaining glycoside hydrolases cleave their substrates through stereochemical retention at the anomeric position. Typically, this involves two-step mechanisms using either an enzymatic nucleophile via a covalent glycosyl enzyme intermediate, or neighboring group participation by a substrate-borne 2-acetamido neighboring group via an oxazoline intermediate; no enzymatic mechanism with participation of the sugar 2-hydroxyl has been reported. Here, we detail structural, computational and kinetic evidence for neighboring group participation by a mannose 2-hydroxyl in glycoside hydrolase family 99 endo-α-1,2-mannanases. We present a series of crystallographic snapshots of key species along the reaction coordinate: a Michaelis complex with a tetrasaccharide substrate; complexes with intermediate mimics, β-1,2-aziridine and β-1,2-epoxide; and a product complex. The 1,2-epoxide intermediate mimic displayed hydrolytic and transfer reactivity analogous to that expected for the 1,2-anhydro sugar intermediate supporting its catalytic equivalence. Quantum mechanics/molecular mechanics modelling of the reaction coordinate predicted a reaction pathway through a 1,2-anhydro sugar via a transition state in an unprecedented flattened, envelope (<i>E</i><sub>3</sub>) conformation. Kinetic isotope effects for anomeric-<sup>2</sup>H and anomeric-<sup>13</sup>C support an oxocarbenium ion-like transition state and that for C2-<sup>18</sup>O (1.052 ± 0.006) directly implicates nucleophilic participation by the C2-hydroxyl. Collectively, these data substantiate this unprecedented and long-imagined enzymatic mechanism.</div><div><br></div>

scholarly journals An Epoxide Intermediate in Glycosidase Catalysis

2019 ◽  
Author(s):  
Lukasz F. Sobala ◽  
Gaetano Speciale ◽  
Sha Zhu ◽  
Lluís Raich ◽  
Natalia Sannikova ◽  
...  
Keyword(s):  
Transition State ◽  
Reaction Pathway ◽  
Reaction Coordinate ◽  
Glycoside Hydrolases ◽  
Glycoside Hydrolase Family ◽  
Neighboring Group ◽  
Group Participation ◽  
Enzymatic Mechanism ◽  
Key Species ◽  
Neighboring Group Participation

<div>Retaining glycoside hydrolases cleave their substrates through stereochemical retention at the anomeric position. Typically, this involves two-step mechanisms using either an enzymatic nucleophile via a covalent glycosyl enzyme intermediate, or neighboring group participation by a substrate-borne 2-acetamido neighboring group via an oxazoline intermediate; no enzymatic mechanism with participation of the sugar 2-hydroxyl has been reported. Here, we detail structural, computational and kinetic evidence for neighboring group participation by a mannose 2-hydroxyl in glycoside hydrolase family 99 endo-α-1,2-mannanases. We present a series of crystallographic snapshots of key species along the reaction coordinate: a Michaelis complex with a tetrasaccharide substrate; complexes with intermediate mimics, β-1,2-aziridine and β-1,2-epoxide; and a product complex. The 1,2-epoxide intermediate mimic displayed hydrolytic and transfer reactivity analogous to that expected for the 1,2-anhydro sugar intermediate supporting its catalytic equivalence. Quantum mechanics/molecular mechanics modelling of the reaction coordinate predicted a reaction pathway through a 1,2-anhydro sugar via a transition state in an unprecedented flattened, envelope (<i>E</i><sub>3</sub>) conformation. Kinetic isotope effects for anomeric-<sup>2</sup>H and anomeric-<sup>13</sup>C support an oxocarbenium ion-like transition state and that for C2-<sup>18</sup>O (1.052 ± 0.006) directly implicates nucleophilic participation by the C2-hydroxyl. Collectively, these data substantiate this unprecedented and long-imagined enzymatic mechanism.</div><div><br></div>

Neighboring group participation in hypobromous acid addition to 19-substituted 5α-cholest-1-enes and in acid cleavage of their epoxy analogs

1982 ◽  
Vol 47 (11) ◽  
pp. 3062-3076 ◽  
Author(s):  
Václav Černý ◽  
Pavel Kočovský
Keyword(s):  
Neighboring Group ◽  
Group Participation ◽  
Acid Addition ◽  
Acid Cleavage ◽  
Hypobromous Acid ◽  
Neighboring Group Participation

Reactions of the title compounds (bearing an OH, OCH3 or OCOCH3 group at C(19)) involve 5(O)n, 7(O)π,n-participation by the 19-substituent or attack by an external nucleophile. The 6(O)π,n-participation does not occur. The behavior of 1,2-unsaturated (or epoxidated) compounds has been compared with the earlier described 2,3-unsaturated or epoxidated analogs. The 1,2-type is genarally less prone to participation. The reasons for this behavior are discussed.

Mechanism of acid cleavage of some steroid epoxides. Competition between neighboring group participation and external nucleophile attack

1982 ◽  
Vol 47 (1) ◽  
pp. 124-129 ◽  
Author(s):  
Pavel Kočovský ◽  
František Tureček ◽  
Václav Černý
Keyword(s):  
Perchloric Acid ◽  
Cyclic Ether ◽  
Oxirane Ring ◽  
Neighboring Group ◽  
Group Participation ◽  
Acid Cleavage ◽  
Neighboring Group Participation

The mechanism of perchloric acid cleavage of epoxides I and II was established on the basis of experiments using H2 18O. The 2α,3α-epoxide I gave two products: the cyclic ether V (60%) arising by 5(O)n participation of the 19-acetoxyl and the diol VI (40%). The latter compound is formed by two mechanisms: 1) By direct cleavage of the oxirane ring with H2 18O as external nucleophile and 2) by 7(O)π,n participation via the ion III. Under the same conditions the 5α,6α-epoxide II yielded two diols: The diequatorial diol VIII (96%) arising by 6(O)π,n participation and the diaxial diol IX which is again formed by both direct cleavage of the oxirane ring with H2 18O and by 7(O)π,n participation via the intermediate ion X. The competition of several mechanisms is discussed.

ChemInform Abstract: Remote Asymmetric Induction Using Neighboring Group Participation of a Sulfenyl Group.

ChemInform ◽  
2010 ◽  
Vol 25 (49) ◽  
pp. no-no
Author(s):  
Y. HASHIMOTO ◽  
Y. SATO ◽  
N. TAKESHITA ◽  
K. KUDO ◽  
K. SAIGO
Keyword(s):  
Asymmetric Induction ◽  
Neighboring Group ◽  
Group Participation ◽  
Neighboring Group Participation

Neighboring group participation in radicals: pulse radiolysis studies on radicals with sulfur-oxygen interaction [Erratum to document cited in CA107(11):96206Y]

1988 ◽  
Vol 53 (21) ◽  
pp. 5192-5192
Author(s):  
Sabine Mahling ◽  
Klaus Dieter Asmus ◽  
Richard S. Glass ◽  
Massoud Hojjatie ◽  
Mahmaad Sabahi ◽  
...  
Keyword(s):  
Pulse Radiolysis ◽  
Neighboring Group ◽  
Group Participation ◽  
Neighboring Group Participation ◽  
Oxygen Interaction
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