Preparation of unsaturated carbohydrates. A facile synthesis of methyl 4,6- O -Benzylidene- D -hex-2-enopyranosides

This paper is dedicated to Prof. Raymond U . Lemieux on the occasion of his 60th birthday HANS H. BAERand ZAHER S. HANNA. Can. J. Chem. 59,889 (1981). Ethyl 4,6-di-0-acetyl-2,3-dideoxy-a-~-erythro-hex-2-enopyranoside (1) in the presence of triphenylphosphine and a catalytic amount of tetrakis(triphenylphosphine)palladium(O) reacted with a variety of amines or with reactive methylene compounds to give high yields of products aminated or C-alkylated, respectively, in an allylic position. Some analogous experiments were performed using the P-D-erythro anomer (2) and the a-D-threo epimer (3) of 1. The constitutions and configurations of the new products were established by means of mass spectra, 13C-and 'H-nmr spectra, and optical rotation data. The reactions of 1 were found to be highly regio-and stereoselective, giving almost exclusively Csubstituted 2-enopyranosides with retention of configuration, except in the case of dibenzylamine which produced a mlxture of the corresponding enoside and its 2-substituted, 3,Cunsaturated isomer having the a-D-threo configuration. The reactions of 2 appeared slightly less selective although they, too, furnished mainly 4-substituted 2-enopyranosldes with retention of configuration. Regioselectivity was low or lacking in two C-alkylations performed with 3, which gave mixtures of Csubstituted 2-enosides and 2-substituted 3-enosides. Some aspects of conformation and optical rotation in enopyranosides are discussed.HANS H. BAER et ZAHER S. HANNA. Can. J. Chem. 59,889 (1981).L e compose C t h y l -4 , 6 -d i -O -a c e t y I -2 , 3 -d i d e s o x y -a -~n o p y r a n o s i d e Introductioncally substituted product. The palladium species Recently we communicated (1) the first results of liberated upon collapse of the intermediary corna study concerning the potential utility of or-plex is reconverted into a catalytically active form ganopalladium reagents for the functionalization of by the action of the excess of triphenylphosphine carbohydrates. The present article reports full de-which is provided. A high degree of regioselectivity tails of the work and includes some additional re-and stereocontrol is normally observed in these sults which have since been elaborated. In connec-substitutions (6), although certain exceptions to tion with our current interest in the development of this welcome trend have been noted and discussed. methods for the synthesis of unusual amino, deoxy, As Our chief substrate for an the unsaturated, and branched-chain sugars (2), we de-utility of the method in the carbohydrate field,[ we cided to examine whether the palladium-catalyzed chose the crystalline ethyl 4,6-di-0-acetyl-2,3-disubstitution of allylic acetates by amines or reac-de0xy-cr-~-er~thro-hex-2-eno~~ranoside (I). his tive methylene compounds (3-6) might be em-compound is readily prepared (9) from commerplayed to advantage in carbohydrate chemistry. In c i a l l~ available D-glucal tfiacetate-For some anthis reaction, which represents one of the numer-cillary experiments, to be performed in the ...

Section: 'H Nuclear Magnetic Resonance Spectrasupporting

confidence: 88%

Section: 'H Nuclear Magnetic Resonance Spectrasupporting

confidence: 87%

Section: 'H Nuclear Magnetic Resonance Spectramentioning

confidence: 99%

See 1 more Smart Citation

The preparation of amino sugars and branched-chain sugars by palladium-catalyzed, allylic substitution of alkyl hex-2-enopyranosides

Baer¹,

Hanna²

1981

“…The starting alcohol (14) was prepared as previously reported (26). Glycosylation of 14 with acetobromoarabinose (7) under Helferich conditions produced 15, which on deacetylation provided the p-linked disaccharide (16) in 54% yield.…”

Section: Et3nmentioning

confidence: 99%

Molecular recognition XI. The synthesis of extensively deoxygenated derivatives of the H-type 2 human blood group determinant and their binding by an anti-H-type 2 monoclonal antibody and the lectin 1 of Ulexeuropaeus

Spohr¹,

Paszkiewicz-Hnatiw²,

Morishima³

et al. 1992

ULRIKE SPOHR, EUGENIA PASZKIEWICZ-HNATIW, NAOHIKO MORISHIMA, and RAYMOND U. LEMIEUX. Can. J . Chem. 70, 254 (1992).The relative potencies of a wide variety of deoxygenated derivatives of the methyl glycoside of a-L-Fuc-(1 -+ 2)-P-D-Gal-(1 -+ 4)-p-~-GlcNAc (the H-type 2 human blood group related trisaccharide) for the inhibition of the binding of an artificial H-type 2 antigen by the lectin I of Ulex europaeus confirmed the previous evidence that the key and productive interaction involves only the three hydroxyl groups of the a-L-fucose unit, the hydroxyl at the 3-position of the P-D-galactose residue, and the nonpolar groups in their immediate environment. Except for the acetamido group and the hydroxymethyl of the P -D -G~~ unit, which stay in the aqueous phase, on complex formation the remaining three hydroxyl groups appear to come to reside at or near the periphery of the combining site since their replacement by hydrogen causes relatively small changes (<* 1 kcal/mol) in the stability of the complex (AGO). Relatively much larger but compensating changes occur for the enthalpy and entropy terms, and these may arise primarily from the differences in the water structure about the periphery of the combining site and the oligosaccharide both prior to and after complexation. It is proposed that steric constraints lead to an ordered state of the water molecules hydrogen-bonded to the polar groups within the cleft formed by the key region of the amphiphilic combining site. Their release to form less ordered clusters of more strongly hydrogen-bonded water molecules in bulk solution would contribute importantly to the driving force for complexation. It is demonstrated that the surface used for the binding of H-type 2-OMe by a monoclonal anti-H antibody is virtually identical to that used by the Ulex lectin.Key words: molecular recognition, H-type 2 blood group determinant and deoxygenated derivatives, lectin I of Ulex europaeus, anti-H-type 2 monoclonal antibody, enthalpy-entropy compensation. Les efficacitCs relatives d'un grand nombre de dCrivCs dCsoxygCnCs du glycoside de mCthyle de l'a-L-Fuc-(I -+ 2)-P-D-Gal-(I -+ 4)-P-D-GlcNAc (trisaccharide reliC au groupe sanguin H de type 2 de l'homme) comme inhibiteurs de la fixation d'un antigkne artificiel du H de type 2 par la lectine I de 1'Ule.x europaeus ont confirmi les donnCes antCrieures suggCrant que cette interaction importante et productive n'implique que les trois groupes hydroxyles de I'unitC a-L-fucose, le groupe hydroxyle.en position 3 du rCsidu P-D-galactose et les groupes non-polaires qui se trouvent dans leur environnement immCdiat. A l'exception du groupe acetamido et de I'hydroxymCthyle de I'unitC P-D-Gal qui restent dans la phase aqueuse lors de la formation du complexe, il semble que les trois autres groupes hydroxyles se retrouvent a, ou pres de, la pCriphCrie du site qui effectue la combinaison; en effet, leur remplacement par de l'hydrogkne ne provoque que de faibles changements (<* 1 kcal/mol) dans la stabilitk du complexe (AGO). Des changements r...

“…Methyl 3-deoxy-P-L-erythro-pentopyranoside (1) was prepared by reactioil of methyl 4-0-acetyl-2,3-anhydro-P-L-ribopyranoside (2) with sodium iodide in acid acetone (3) followed by hydrogenolysis of the resulting methyl 4-0-acetyl-3-deoxy-3-iodo-P-L-xylopyranoside using palladium on carbon as catalyst. The deacetylated product was converted to the di-0-pnitrobenzoate of 1, m.p.…”

mentioning

confidence: 99%

Correlation of specific rotation with conformation. A new approach to the study of conformational equilibria

Lemieux¹,

Pavia²

1968

Self Cite

The marked changes in optical rotation which occur on dissolving the methyl 2-deoxy-a-L-and 3-deoxy-p-L-erytlzro-pentopyranosides in a variety of solvents including chloroform, acetone, acetonitrile, pyridine, dimethylsulfoxide, and water were found by nuclear magnetic resonance to result alnlost exclusively from changes in conformational equilibria. The changes in rotation are in agreement with those expected from Brewster's rules.Canadian Journal of Chemistry. 46, 1453Chemistry. 46, (1968 The profound influence of solvent on the conformational properties of methyl 2-deoxya-D-evythro-pentopyranoside (1) prompted a further examination of this and related phenomena.Methyl 3-deoxy-P-L-erythro-pentopyranoside (1) was prepared by reactioil of methyl 4-0-acetyl-2,3-anhydro-P-L-ribopyranoside (2) with sodium iodide in acid acetone (3) followed by hydrogenolysis of the resulting methyl 4-0-acetyl-3-deoxy-3-iodo-P-L-xylopyranoside using palladium on carbon as catalyst. The deacetylated product was converted to the di-0-pnitrobenzoate of 1, m.p. 123.5-1 24.5", [a], +51.2" (c, 1.3 in chloroform) for purification. Saponification followed by vacuum distillation afforded analytically pure 1 as a colorless oil.The nuclear magnetic resonance (n.m.r.) spectrum of 1 in deuterium oxide required the compound to exist largely in the 1C conformation (lb) since J, , , = 6.0, J,, , -J,,, -8.9, J,, , , -J3.,,=4.5, and J,,,,,= 1.9 Hz. In this conformation, the compound is expected (4) to possess a specific rotation of + 100". A specific 'University of Alberta Postdoctorate Fellow, 1967 rotation of +95" was observed. When deuteriochloroform was used as solvent, J1,, decreased to 2.2 Hz and it was clearly evident that H, and H,, were weakly (< 3 Hz) coupled with both H, and H,. Similarly H, was weakly coupled with both H, and H,,. It was therefore apparent that the compound now existed largely in the C1 conformation (la). Indeed, for the coinpound in this conformation a specific rotation of + 137" is expected and the value observed was +142". It was possible to show that the relative chemical shifts observed for the various ring protons were in good agreement with those expected based on the empirical rules proposed by Lemieux and Stevens (5).The above data infer that the change in rotation was to a good approximation the result of the change in conformational equilibria which occurred on changing the solvent. It could be expected, therefore, that in such situations studies of change in conformation with change in environment could be examined by simple polarimetry. To test this hypothesis, the rotations and n.m.r. spectra of compound 1 were measured in a variety of solvents. The results presented in Fig. 1 show that a linear relationship was obtained between the coupliilg constant of H, with H z (J,,, as displayed by the spacing of the doublet for H I ) with the specific rotation. The value for J,,, is considered to be a measure of the relative populations of the conformations l a and l b for 1.Preliminary studies with the a and P auom...