Non-reducing Units Research Articles

Synthesis of flavonoid glycosides. Part XII. Synthesis of some disaccharides containing rhamnose as the nonreducing unit.

Synthesis of flavonoid glycosides. Part XII. Synthesis of some disaccharides containing rhamnose as the nonreducing unit.

Mass spectra of permethylates of spirostanol tetraosides

The design of the new MKh 1310 mass spectrometer with double focusing permits the recording of the spectra of sparingly volatile natural compounds with molecular weights of up to 1700 and, in particular, the permethylates and peracetates of spirostanol and furostanol saponins. The results are given of an investigation of the mass spectra of five spirostanol tetraosides in the form of their permethylates. The spectra contain the peaks of the molecular ions and of the products of their decomposition at the glycosidic bonds. The most important feature of the spectra is the fragmentation of the skeletons of the terminal saccharide residues starting directly from M+ in directions close to the directions of decomposition of the nonreducing unit of permethylates of oligosaccharides. The origin of the ions (M -191)+, (M - 175)+, (M - 162)+, (M - 147)+, (M - 131)+, (M - 118)+, and (M - 102)+ arising this way have been confirmed by measurements of their elementary compositions.

Stereoselective dienyl ether syntheses from malonaldehyde trans-enol ethers: (E)-buta-1,3-dienyl, and (E,Z)- and (E,E)-4-chlorobuta-1,3-dienyl ethers of a protected sugar; conversion of the latter into functionalized chiral disaccharide precursors

Condensation of the enol tosylate of malonaldehyde with the sodium alcoholate NaOR derived from ‘diacetone glucose’ gave in 92% yield the almost pure trans-enol ether RO–CHCH–CHO (1). This could be readily condensed with suitable Wittig phosphoranes to give either the buta-1,3-dienyl ether (2)(87% yield; more than 90%trans), or a mixture of 4-chlorobuta-1,3-dienyl ethers (85%) of ‘diacetone glucose;’ the main components were the (E,Z)-diene (5)(45%) and the (E,E)-diene (4)(45%). Cycloaddition of diethyl mesoxalate to the diene (4) gave a mixture of two 3-chloro-2, 2-bisethoxycarbonyl-3,6-dihydro-2H-pyran-6-yl ethers, the (3S,6S)-derivative (6)(69%) and the (3R,6R)-derivative (7)(19%). Free-radical reduction of these chlorides (6) and (7) with tributylstannane led to mainly rearranged products: the 2, 2-bisethoxycarbonyl-5, 6-dihydro-2H-pyran-6-yl ethers, (6S)(9) and (6R)(11). In the same way, nucleophilic substitution of the chloride (6) with azide led to the (5S)-5-azido-derivative (12) of the dihydropyran (9). Catalytic reduction of the double bond and the azido group in (12), followed by N-acetylation, gave the saturated (S)-acetamido derivative (13), which could be deethoxycarbonylated to give two disaccharides with a 2-acetamido-2-deoxyhexopyranosyl non-reducing unit. We consider that the above overall sequence of reactions is a useful extension of the cycloaddition method of disaccharide synthesis.

The 13C-n.m.r. spectra of disaccharides of d-glucose, d-galactose, and l-rhamnose as models for immununological polysaccharides

Complete assignments of the 13C-n.m.r. spectra of disaccharides having β-glycosidic linkages are presented and discussed. The disaccharides of d-glucose, d-galactose, l-rhamnose, 2-acetamido-2-deoxy- d-glucose, and 2-acetamido-2-deoxy- d-galactose are model compounds for 13C-n.m.r. studies of immunological polysaccharides. Changing the nature of the reducing glucopyranose rings ( d-glucose to l-rhamnose) has no important influence on the chemical shifts of the carbons of the non-reducing glueopyranose ring ( d-glucose). The converse is also true: the chemical shifts of the carbons of the reducing glucopyranose ring (L-rhamnose) are not noticeably affected by a change of the non-reducing unit ( d-glucose to d-galactose or 2-acetamido-2-deoxy- d-glucose).

The carbohydrates of the roots of the sugar maple

Alkaline extraction of the chlorite holocellulose from the roots of the sugar maple (Acer saccharum) yielded a mixture of hemicellulose material which gave glucose, xylose, galactose, an acidic component, and arabinose in the approximate molar ratio of 14:22:1.7:1.9:1.0 upon acid hydrolysis. This crude hemicellulose was separated into four fractions by differential precipitation with Cetavlon. Methylation of two of these hemicelluloses resulted in further purification, and yielded two acidic glucoxylans (B-1-A and B-3-A) which were structurally distinct from the polysaccharides found in the shoot. Fraction B-l-A (degree of polymerization 144) consisted of a chain of β-(1 → 4)-linked d-xylose and d-glucose units, some of each of which were branched through C-3. The terminal, nonreducing units were d-xylose or sugar acid residues. Fraction B-3-A (degree of polymerization 96) also consisted of a chain of β-(l → 4)-linked d-xylose and d-glucose units, but branching occurred at C-3 of some of the d-xylose residues only. The carbohydrate composition of the mono- and oligo-saccharide fractions and of the other hemicelluloses was investigated.

Some considerations of the kinetics of the acid hydrolysis of poly‐ and oligosaccharides. II. The trisaccharides, isomaltotriitol, panitol, and isomaltotriose

AbstractOn the basis of the rate data of Jones, Dimler, and Rist on the acid‐catalyzed hydrolysis of isomaltotriitol it is shown that the kinetics can be described by rate equations derived by assuming a combination of two interdependent simultaneous (“parallel”) and consecutive reactions according to the scheme: magnified image where A is isomaltotriitol; (B), B, and B* are glucose; C is isomaltitol; D and (D) are sorbitol; and E is isomaltose present at any instant; k1 and k2 are specific rates at which the two glucosidic bonds are hydrolytically cleaved in isomaltotriitol; k3 is the specific rate of hydrolysis of isomaltitol (known); and k4 is the specific rate of hydrolysis of isomaltose (known). Values for the constants k1 and k3 have been computed from the experimental values of the composition of the hydrolysis reaction mixture and the known values for k2 and k4. The yields of glucose and sorbitol as well as the extent of hydrolysis have then been calculated using the values for k1 and k3 (computed) and k2 and k4 (known) by means of rate equations corresponding to the above scheme. They are in very good agreement with the experimental values. The kinetics of the acid hydrolysis of isomaltotriose can also be described by rate equations corresponding to a kinetic scheme: magnified image where A″ is isomaltotriose; (B″), B″, B″*, and B**″ are glucose; (C″) and C″ are isomaltose at any instant; k5 and k6 are the specific rates of hydrolytic cleavage of the two glucosidic bonds in isomaltotriose, and k4 is the specific rate of hydrolysis if isomaltose (known). Assuming that k5 = k4/1.3 and k6 = k4/1.5, values for the extent of hydrolysis (expressed in terms of glucosidic bond cleavage for 100 bonds) have been calculated by means of rate equations derived on the basis of the above scheme. They show good agreement with the experimental values. However, transposing the values for k5 and k6 does not alter the calculated values. Thus, only the following conclusions seem to be permissible: the glucosidic bonds in isomaltotriose most likely hydrolyze at a lower rate than isomaltose; the two bonds do not hydrolyze at the same rate; whether the rate of hydrolysis of the glucosidic link of the reducing unit is slower than that of the nonreducing unit or the reverse, remains to be established. Attention is drawn to the role of the theoretical carbohydrate structural chemist who may offer an explanation for the deductions of the kineticist in the field of both trisaccharide and disaccharide hydrolysis.

ISOLATION OF 2 SEROLOGICALLY ACTIVE TRISACCHARIDES FROM HUMAN BLOOD-GROUP B SUBSTANCE.

A PREVIOUS communication1 reported the isolation of a B-active disaccharide, identified as 3-O-α-D-galacto-pyranosyl-D-galactoso, from the products of partial acid-hydrolysis of a human blood-group B specific mucopolysaccharide. This sugar was the only disaccharide detected that showed B-activity, and its absence from the hydrolysis products of human blood-group A specific substance2,3, together with other evidence, led us to infer that this disaccharide is the terminal non-reducing unit of the blood-group B determinant structure in the original mucopolysaccharide. However, the capacity of the disaccharide to inhibit the agglutination of B erythrocytes by a human anti-B serum, although much greater than that of any simple sugar previously examined, was nevertheless much lower than that of the intact B-active mucopolysaccharide in the same system, thus supporting the idea1,4 that the complete B-determinant structure is larger than a disaccharide unit. To investigate this possibility, the trisaccharide components in the hydrolysis products were examined, and the isolation and identification of two B-active trisaccharides are now described.