Failure of the antiperiplanar lone pair hypothesis in glycoside hydrolysis. Synthesis, conformation, and hydrolysis of α-<scp>D</scp>-xylopyranosyl-and α-<scp>D</scp>-glucopyranosyl-pyridinium salts

Hosie, L; Marshall, Philip J.; Sinnott, Michael L.

doi:10.1039/p29840001121

Cited by 53 publications

(54 citation statements)

References 3 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…This implies a 1 S 3 → 4 H 3 → 4 C 1 pseudorotational itinerary for the glycosylation step of the retaining mechanism (Scheme ). Other glycoside conformations can, however, also place the C5, O5, C1, and C2 atoms within a plane, such as the 3 H 4 half chair and both 2,5 B B 2,5 boats 6. Indeed, family‐11 xylanases display a covalent xylobiosyl–enzyme intermediate in a 2,5 B boat conformation,7 suggesting that a similar conformation is also adopted at the transition state for this class of enzymes, as had previously been suggested for yeast α ‐glucosidase on the basis of kinetic isotope effects 8…”

Section: Methodsmentioning

confidence: 99%

Substrate Distortion by aβ-Mannanase: Snapshots of the Michaelis and Covalent-Intermediate Complexes Suggest aB2,5 Conformation for the Transition State

et al. 2002

View full text Add to dashboard Cite

More than 6000 glycosidase sequences and related open reading frames are currently known. They have been classified into some 85 families based upon amino acid sequence similarities [1] providing a rich context in which to explore variations in glycosidase mechanism. Experimental demonstration of pyranoside ring conformations along the reaction pathway may assist the design of transition state analogues both as therapeutic agents and mechanistic probes. Here we report the three-dimensional structures of the Michaelis complex and covalent glycosyl ± enzyme intermediate for a family-26 b-mannanase, both of which display conformational features never previously seen on any glycosidase. When viewed in light of published work on mannosidase inhibition, this work suggests that the transition state for mannoside conditions to those described in Figure 4. These magnetic data are very similar to recent experimental results reported by other groups on complexes of Cu 2 dimers. [26] Theoretical fit using the BB model to the temperature-dependent molar susceptibility data in this case yields fit parameters J À 380 cm À1 and J' À 85 cm À1 . Clearly, the most striking feature is that the field-dependent magnetization does not display a hysteresis loop in this system, the straight line obtained being representative of a more traditional paramagnetic behavior.Our results dramatically underscore the potential afforded by supramolecular chemistry for the design of molecular nanostructured assemblies with desirable physical properties, while emphasizing how the composition of a material is not the only feature one must consider when designing a phase that exhibits molecular magnetism. Future work will focus on the modularity of this system and on chemical modification of the components: substituting the metal; changing the coordinated ligand; substituting the bdc ligand; incorporation of different guest molecules. We expect a significant effect on magnetic properties as it has already been shown that simply varying the apical coordinated ligand has a measurable effect on the magnetism exhibited by the SBU used in our study. Intensity data for 1 were collected at 173 K on a Bruker SMART-APEX diffractometer using Mo Ka radiation (l 0.7107 ä): Cu 6 C 123.08 H 54 N 9.37 O 30.73 , 2536.69 g mol À1 , trigonal, space group P3 ≈ c1, a b 18.6523(11), c 19.8313(18) ä, V 5975.1(7) ä 3 , Z 2, 1 calcd 1.410 g cm À3 , m 1.128 mm À1 , F(000) 2556, 2q max 50.08. Final residuals (for 265 parameters) were R1 0.0491 for 2112 reflections with I > 2sI, and R1 0.0764, wR2 0.1577, GoF 0.985 for all 3520 data. Residual electron density was 0.753 and À 0.574 e ä À3 . Highly disordered solvent molecules in the hexagonal channels were modeled as a group of variable-occupancy carbon atoms. CCDC-165791 contains the supplementary crystallographic

show abstract

Section: Methodsmentioning

confidence: 99%

Substrate Distortion by aβ-Mannanase: Snapshots of the Michaelis and Covalent-Intermediate Complexes Suggest aB2,5 Conformation for the Transition State

et al. 2002

View full text Add to dashboard Cite

show abstract

“…The one compelling demonstration of the existence of a phenomenon of some sort related to ALPH is the detection of w-aminoamides as kinetic products, and lactams as thermodynamic products, in the hydrolysis of 5and 6-membered cyclic amidines (Perrin & Arrhenius, 1982). We have since shown (Hosie et al, 1984) that this result is also predicted by the principle of least nuclear motion. Arguments exactly analogous to those presented in Hosie et al (1984) immediately explain the results with cyclic orthoesters, without any further ad hoc hypotheses.…”

mentioning

confidence: 86%

“…As explained above, this rationalization violates the Curtin-Hammett principle, but it is possible, if assumptions are made about the relationship between transition state conformation and reactive ground state conformation, to examine the supplementary hypothesis of reaction through nonground-state conformers using the leaving group as a conformational determinant. We have done this with anomeric pairs of glycosyl pyridinium salts, and have shown the supplementary hypothesis to be untenable (Hosie et al, 1984).…”

mentioning

confidence: 99%

On the antiperiplanar lone pair hypothesis and its application to catalysis by glycosidases

Sinnott¹

1984

Biochemical Journal

View full text Add to dashboard Cite

The idea that sp3 lone pairs of electrons on a heteroatom direct the departure of a leaving group from an adjacent tetrahedral carbon centre is shown to be untenable as a general principle, and the permissive evidence in favour of it to be accounted for by the principle of least nuclear motion. The application of the idea to the majority of glycopyranosidases, which work by a double-displacement mechanism, is shown to require implausible contortions of the pyranose ring.

show abstract

“…Numerous other examples have, moreover, been reported in which bonds with antiperiplanar lone electron pairs react more slowly than, or at rates similar to, comparable bonds without antiperiplanar lone pairs [52,[63][64][65][66][67].…”

Section: Other Reactionsmentioning

confidence: 99%

Stereoelectronic Effects and Reactivity

Dörwald

2004

Side Reactions in Organic Synthesis

View full text Add to dashboard Cite

Hyperconjugation with r BondsStereoelectronic effects can be defined as effects on structure and reactivity determined by the efficiency of orbital overlap as a function of molecular conformation. Interactions involving sp 3 hybrid orbitals are usually referred to as "hyperconjugation", whereas interactions of p orbitals of sp 2 hybridized atoms are called "conjugation". Hyperconjugation will stabilize or destabilize certain conformations, strengthen or weaken bonds, and can increase or reduce the energy of lone electron pairs, and thereby modulate the nucleophilicity and basicity of a given compound. Those stereoelectronic effects with highest impact on the reactivity of compounds generally result from interaction of vicinal orbitals.In Scheme 2.1 the orbital interactions between two sp 3 hybridized, tetravalent atoms X and Y are sketched in the staggered conformation. This conformation enables efficient transfer of electrons from the (bonding) r X-A orbital to the empty (antibonding) r* X-A orbital; this leads to longer and weaker X-A bonds and a shorter, stronger X-Y bond. The net effect is lowering of the ground state energy (i.e. stabilization) of the molecule. This form of hyperconjugation can also be illustrated by the two canonical forms sketched in Scheme 2.1.In principle a r X-A fi r* Y-A charge-transfer interaction would also be possible when the two vicinal X-A and Y-A bonds adopt a synperiplanar conformation. However, in this latter conformation the overlap integral r X-A fi r* Y-A and thus the Scheme 2.1. Orbital interaction and canonical forms for hyperconjugation between r bonds.

show abstract

Failure of the antiperiplanar lone pair hypothesis in glycoside hydrolysis. Synthesis, conformation, and hydrolysis of α-D-xylopyranosyl-and α-D-glucopyranosyl-pyridinium salts

Cited by 53 publications

References 3 publications

Substrate Distortion by aβ-Mannanase: Snapshots of the Michaelis and Covalent-Intermediate Complexes Suggest aB2,5 Conformation for the Transition State

Substrate Distortion by aβ-Mannanase: Snapshots of the Michaelis and Covalent-Intermediate Complexes Suggest aB2,5 Conformation for the Transition State

On the antiperiplanar lone pair hypothesis and its application to catalysis by glycosidases

Stereoelectronic Effects and Reactivity

Contact Info

Product

Resources

About