THE EFFECT OF CHLORINE SUBSTITUTIONS AT THE C 2 -ACETOXY GROUP ON SOME PROPERTIES OF THE GLUCOSE PENTAACETATES

The complete structures of the major components of the mixture of lactonic and acidic sophorosides of 17-L-hydroxyoctadecanoic acid, which is produced by a yeast of the genus Tor~rlopsis, have been determined. The principal lactonic component (1) (41 %) has acetate groups at the 6'-and 6"-positions and the fatty acid carboxyl group is linked to the 4"-position to form a macrocyclic lactone ring. Theother lactonic component (2) (8 %) differs from the first only in the absence of the acetate group at the 6'-position. T h e principal acidic component (5) (3 1 %)also has acetate groups at the 6'-and 6''-positions but the fatty acid carboxyl group is free. The structures were deduced by a combination of glycol cleavage and nuclear magnetic resonance studies and by examination of the products of acctobrominolysis of the acetylated lactones and acid.The 2",3"-glycol group of the lactones is resistant to oxidation by periodate and by lead tetraacetate in acetic acid. Studies of the rate of glycol cleavage of methyl 4,6-di-0-acyl-0-D-glucopyranosides showed that though an acyl group at C-4 retarded the oxidation of the 2,3-diol it did not stop it completely. The conformation of the lactone ring is probably responsible for the unreactivity of the 2",3"-glycol group. The lactone ring, however, considerably increases the rate of acetobron~inolysis of the fully acetylated lactone compared to that of the acetylated sophorosyl acid n~ethyl ester.

Section: Position Of Lactolze Rilzg Of 1 Andmentioning

confidence: 56%

Section: Nuclear Magnetic Resonar7ce Spectramentioning

confidence: 92%

Structure and reactions of lactonic and acidic sophorosides of 17-hydroxyoctadecanoic acid

Tulloch¹,

Hill²,

Spencer³

1968

“…There are many examples of acid-catalysed glycoside anomerization and their mechanisms are reasonably well understood (1)(2)(3)(4)(5)(6)(7). In all cases studied to date, including simple alkyl glycosides (1-3), protected alkyl glycosides (4), or fully acetylated sugars (5-7), the mechanism has involved oxocarbonium ion intermediates, whether catalysed by a Lewis or a Br~nsted acid.…”

Section: Introductionmentioning

confidence: 99%

The base-catalysed anomerization of dinitrophenyl glycosides: evidence for a novel reaction mechanism

Berven¹,

Dolphin²,

Withers³

1990

The mechanism of base-catalysed anomerization of per-0-acetylated 2, 4-dinitrophenyl-0-D-glucopyranoside in dimethy Isulfoxide has been investigated using a variety of techniques. A mechanism involving proton abstraction at C-1 was eliminated by the absence of proton exchange at that center and the measurement of a secondary deuterium kinetic isotope effect for the 1-deuterio substrate. A mechanism involving phenolate departure and recombination is rendered unlikely on the basis of remote substituent effects on the reaction rate and by the absence of any exchange of the phenyl moiety with added phenolate. A mechanism involving nucleophilic aromatic substitution initiated by an attack of the dimethylsulfinyl anion to generate a glucosyl oxyanion intermediate that anomerizes and recombines with the reactive aryl intermediate is consistent with the observations. This mechanism is further supported by the observation of a purple Meisenheimer complex intermediate and by the observed exchange between the substrate containing a labelled sugar moiety and added unlabelled 2,3,4,6-tetra-0-acetyl-P-D-glucopyranose.

“…Certainly the removal of the C-2 chlorosulfate group would contribute to a more rapid solvolysis as it has been demonstrated that the removal of a non-participating trichloroacetate group from the C-2 position of a glucopyranosyl chloride derivative does considerably enhance the rate of solvolysis (5). This has been attributed to a decrease in steric hindrance at the anomeric center (5), although the importance of the contribution of electronic factors has also been clearly demonstrated (6). It is also probable that the removal of the C-3 and -4 chlorosulfate groups from 1 would further assist in the solvolytic process, as it has been demonstrated that other groups besides the one situated at C-2 of glycopyranosyl halides do have some effect on the relative rates of anomeric exchange reactions (7, 8).…”

mentioning

confidence: 99%

Methyl Glycosidation and Methyl Thioglycosidation of Some Fully Chlorosulfated Pentopyranosyl Chlorides Using Sodium Iodide as a Catalyst

Jennings¹

1971

The treatment of a-and [I-D-xylopyranosyl chloride 2,3,4-tri(chlorosulfate) and the corresponding a-D-lyxo derivative with a catalytic quantity of sodium iodide in methanol solution resulted in the removal of the chlorosulfate groups and rapid methanolysis of the anomeric chlorine atoms. The methanolysis proceeded with predominant inversion in each case (80-90%), independent of the orientation of the C-2 substituent. I n the presence of sodium methyl mercaptide, however, thioglycosides having an inverted configuration were produced from 1,2-cis chlorides, and thioglycosides having an unchanged anomeric configuration were formed from 1,2-trans chlorides. It is proposed that all these glycosidations occur via a free pentopyranosyl chloride intermediate, and that under the basic conditions of thioglycosidation a 1,2-anhydro intermediate is formed from 1,2-trans chlorides.Le traitement des chloro-l trichlorosulfate-2,3,4 a-et [I-D-xylopyranose et a-D-lyxopyranose par des quantitks catalytiques d'iodure de sodium en solution dans le mkthanol conduit a une solvolyse rapide des groupes chlorosulfates et des atomes de chlore attachks aux carbones anomeriques. Dans chaque cas, la mkthanolyse se produit principalement (80-90%) avec inversion et ceci quelle que soit I'orientation du substituant en position 2. Toutefois, lorsque ces rkactions sont effectukes en prksence du sel de sodium du methanethiol, la stkrkochimie de la reaction depend de l'orientation prksente dans les composks de dkpart; la rkaction des chlorures ayant la configuration cis-1,2 procirde avec inversion alors que celle des dkrivks trans-1,2 se produit avec rktention. On croit que toutes ces rkactions conduisant a des glucosides se produisent par I'intermkdiaire d'un chloro-l pentopyranose; pour ce qui est des thioglucosides formks en milieu alcalin a partir de chlorures trans-1,2; ils proviendraient d'un derivt anhydro-1,2 intermkdiaire. In earlier experiments it has been demonstrated 2,3,4-tri(chlorosu1fate) (1) gave good yields of that chlorosulfate groups can be removed from a mixture of methyl a-and P-D-xylopyranosides. chlorosulfated glycoside derivatives by treat-The methyl a-D-anomer (3) was shown to conment with sodium iodide in aqueous methanol (1). This reaction is very rapid and regenerates the hydroxyl groups with retention of configuration. When glycosyl chlorides containing chlorosulfate groups were treated with sodium iodide in aqueous acetone the reaction involved in addition, hydrolysis of the anomeric chlorine atom, to give the free glycose (2, 3). I t was of interest to study this reaction on chlorosulfated glycosyl chlorides using methanol as the solvent, to ascertain whether methyl glycosidation would occur under these conditions. As in some previously described dechlorosulfations (1, 4), barium carbonate was added in these reactions stitute approximately 90 % of the mixture (g.1.c. analysis), and was isolated and characterized as its triacetate. Thus the methyl glycosidation of 1 occurs predominantly with inversion of configuration...