The syntheses of 6-C-alkyl derivatives of methyl α-isomaltoside for a study of the mechanism of hydrolysis by amyloglucosidase

2001 ◽  
Vol 79 (2) ◽  
pp. 238-255 ◽  
Author(s):  
Ulrike Spohr ◽  
Nghia Le ◽  
Chang-Chun Ling ◽  
Raymond U Lemieux

The epimeric (6aR)- and (6aS)-C-alkyl (methyl, ethyl and isopropyl) derivatives of methyl α-isomaltoside (1) were synthesized in order to examine the effects of introducing alkyl groups of increasing bulk on the rate of catalysis for the hydrolysis of the interunit α-glycosidic bond by the enzyme amyloglucosidase, EC 3.2.1.3, commonly termed glucoamylase (AMG). It was previously established that methyl (6aR)-C-methyl α-isomaltoside is hydrolysed about 2 times faster than methyl α-isomaltoside and about 8 times faster than its S-isomer. The kinetics for the hydrolyses of the ethyl and isopropyl analogs were also recently published. As was expected from molecular model calculations, all the R-epimers are good substrates. A rationale is presented for the catalysis based on conventional mechanistic theories that includes the assistance for the decomposition of the activated complex to products by the presence of a hydrogen bond, which connects the 4a-hydroxyl group to the tryptophane and arginine units. It is proposed that activation of the initially formed complex to the transition state is assisted by the energy released as a result of both of the displacement of perturbed water molecules of hydration at the surfaces of both the polyamphiphilic substrate and the combining site and the establishment of intermolecular hydrogen bonds, i.e., micro-thermodynamics. The dissipation of the heat to the bulk solution is impeded by a shell of aromatic amino acids that surround the combining site. Such shields are known to be located around the combining sites of lectins and carbohydrate specific antibodies and are considered necessary to prevent the disruption of the intermolecular hydrogen bonds, which are of key importance for the stability of the complex. These features together with the exquisite stereoelectronic dispositions of the reacting molecules within the combining site offer a rationalization for the catalysis at ambient temperatures and near neutral pH. The syntheses involved the addition of alkyl Grignard reagents to methyl 6-aldehydo-α-D-glucopyranoside. The addition favoured formation of the S-epimers by over 90%. Useful amounts of the active R-isomers were obtained by epimerization of the chiral centers using conventional methods. Glycosylation of the resulting alcohols under conditions for bromide-ion catalysis, provided methyl (6aS)- and (6aR)-C-alkyl-hepta-O-benzyl-α-isomaltosides. Catalytic hydrogenolysis of the benzyl groups afforded the desired disaccharides. 1H NMR studies established the absolute configurations and provided evidence for conformational preferences.Key words: amyloglucosidase (AMG), exo-anomeric effect, 6-C-alkyl-α-D-glucopyranosides and isomaltosides, mechanism of enzyme catalysis.

2021 ◽  
Vol 1227 ◽  
pp. 129509
Author(s):  
Rimma G. Savchenko ◽  
Ekaterina S. Mescheryakova ◽  
Kamil Sh. Bikmukhametov ◽  
Arthur R. Tulyabaev ◽  
Lyudmila V. Parfenova ◽  
...  

2000 ◽  
Vol 56 (5) ◽  
pp. 882-892 ◽  
Author(s):  
J. N. Low ◽  
M. D. López ◽  
P. Arranz Mascarós ◽  
J. Cobo Domingo ◽  
M. L. Godino ◽  
...  

In each of N-(6-amino-3,4-dihydro-3-methyl-5-nitroso-4-oxopyrimidin-2-yl)valine, C10H15N5O4 (3) (orthorhombic, P212121), N-(6-amino-3,4-dihydro-3-methyl-5-nitroso-4-oxopyrimidin-2-yl)serine monohydrate, C8H11N5O5·H2O (4) (orthorhombic, P212121), and N-(6-amino-3,4-dihydro-3-methyl-5-nitroso-4-oxopyrimidin-2-yl)threonine, C9H13N5O5(5) (monoclinic, P21), the C-nitroso fragments exhibit almost equal C—N and N—O bond lengths: the C—N range is 1.315 (3)–1.329 (3) Å and the N—O range is 1.293 (3)–1.326 (3) Å. In each compound there are also very short intermolecular O—H...O hydrogen bonds, in which carboxyl groups act as hydrogen-bond donors to the nitrosyl O atoms: the O...O distances range from 2.440 (2) to 2.504 (4) Å and the O—H...O angles lie between 161 and 163°. An interpretation of the relationship between the unusual intramolecular bond lengths and the very short intermolecular hydrogen bonds has been developed based on database analysis and computational modelling. In each of (3)–(5) there is an extensive network of intermolecular hydrogen bonds, generating three-dimensional frameworks in (3) and (5), and two-dimensional sheets in (4).


2019 ◽  
Vol 21 (7) ◽  
pp. 3545-3549 ◽  
Author(s):  
Lorenzo Spada ◽  
Iciar Uriarte ◽  
Weixing Li ◽  
Luca Evangelisti ◽  
Emilio J. Cocinero ◽  
...  

The observed spectrum identifies aCssymmetry σ-type complex, with the two subunits held together by coplanar “classical” O–H⋯N and weak C–H⋯π intermolecular hydrogen bonds. The O⋯N distance decreases by 4 mÅ upon deuteration of the hydroxyl group (reverse Ubbelohde effect).


2007 ◽  
Vol 62 (4) ◽  
pp. 519-522 ◽  
Author(s):  
Anvarhusen K. Bilakhiya ◽  
Frank W. Heinemann ◽  
Andreas Grohmann

The reaction of four equivalents of phenyl or tert-butyl isocyanate with the pyridine-derived tetraamine 2,6-C3H3N[CMe(CH2NH2)2]2 in toluene gives high yields of the quadruply ureido substituted products 2,6-C5H3N[CMe(CH2R)2]2 [R = -NH(CO)NHPh and -NH(CO)NHtBu]. Full spectroscopic data for both compounds are given. A single crystal X-ray structure determination of the phenyl derivative reveals an intricate network of both intra- and intermolecular hydrogen bonds involving the C=O and both NH functionalities in all ureido groups.


1997 ◽  
Vol 53 (5) ◽  
pp. 843-848 ◽  
Author(s):  
T. Steiner ◽  
S. A. Mason ◽  
M. Tamm

The neutron diffraction crystal structure of the title compound, C17H12O, was determined at 20 K. One of the benzyl groups accepts intermolecular hydrogen bonds from a hydroxyl and an ethynyl group, one to each face of the ring. The bond donated by the hydroxyl group points almost linearly to an aromatic C atom with a H...C separation of 2.339 (6) Å. The bond donated by the ethynyl group points to the aromatic midpoint M with a H...M separation of 2.587 (5) Å. The average acetylenic C—H bond length determined by low- temperature neutron diffraction is only 1.062 (6) Å, appreciably shorter than observed for chemically different C—H bonds.


1964 ◽  
Vol 17 (8) ◽  
pp. 860 ◽  
Author(s):  
AN Hambly ◽  
BV O'Grady

Spectroscopic evidence for the existence of intermolecular hydrogen bonds between aniline molecules has been obtained. Examples show the existence of intramolecular hydrogen bonds in orthodiamines, some amino-derivatives of heterocycles, 2-nitro-amines, 2-amino-sulphones, and 2-amino-sulphides. Some new observations, which do not agree with Krueger's interpretation of the profile of the overtone bands due to NH2 stretching vibrations, are recorded.


1992 ◽  
Vol 70 (1) ◽  
pp. 241-253 ◽  
Author(s):  
P. V. Nikrad ◽  
H. Beierbeck ◽  
R. U. Lemieux

The relative potencies of both the monodeoxy and mono-O-methyl derivatives of the Leb-OMe tetrasaccharide (α-L-Fuc-(1 → 2)-β-D-Gal-(1 → 3)-[α-L-Fuc-(1 → 4)]-β-D-GlcNAc-OMe) as inhibitors of the complexation of a Leb artificial antigen by the lectin IV of Griffoniasimplicifolia are interpreted in terms of the X-ray crystal structure at 2.5 Å resolution of the GS-IV • Leb-OMe complex. Both kinds of derivatives maintain high potencies when the hydroxyl groups involved appear, in the crystal structure, to be in contact with the aqueous phase. Hydroxyl groups situated at the periphery of the combining site and hydrogen bonded to the protein can also be deoxygenated without important loss in potency. However, their methylation leads to a strong decrease in the stability of the complex, because the steric bulk of the introduced methyl group causes loss of complementarity. In contrast, the hydroxyl groups that form hydrogen bonds with the protein along the base of the shallow amphiphilic cleft of the combining site can neither be deoxygenated nor methylated without virtually complete loss of binding activity. Thus, the procedure can provide an appreciation of the various kinds of hydrogen bonds that are present in a protein • oligosaccharide complex. Hard-sphere calculations supported these contentions since an energetically favorable orientation was indicated for a methoxy group at any one of the five positions that were expected to remain in contact with the aqueous phase. However, the calculations, as expected, showed the introduction of strong destabilizing nonbonded interactions when the methylation involved hydroxyl groups that are hydrogen bonded to the protein in the complex. The results are in accord with the previously made rationalization of the near linear enthalpy–entropy compensation found for the active deoxy congeners. Keywords: molecular recognition, lectin IV of Griffoniasimplicifolia, O-methyl derivatives of the Lewis b-OMe tetrasaccharide, detection of intermolecular hydrogen bonds, hard-sphere calculations.


2014 ◽  
Vol 10 ◽  
pp. 2255-2262 ◽  
Author(s):  
Jan Szabo ◽  
Kerstin Karger ◽  
Nicolas Bucher ◽  
Gerhard Maas

1,2,3-Triaminoguanidinium chloride was combined with benzaldehyde and hydratropic aldehyde to furnish the corresponding tris(imines), which were converted into 1,2,3-tris(benzylamino)guanidinium salts by catalytic hydrogenation in the former, and by borane reduction in the latter case. The resulting alkyl-substituted triaminoguanidinium salts underwent a threefold carbamoylation with aryl isocyanates to furnish 1,2,3-tris(ureido)guanidinium salts, while p-toluenesulfonyl isocyanate led only to a mono-ureido guanidinium salt. With aryl isothiocyanates, 3-hydrazino-1H-1,2,4-triazole-5(4H)-thione derivatives were obtained. Compounds 7a and 8 show interesting solid-state structures with intra- and intermolecular hydrogen bonds.


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