Native dextran

Fig. 5.11. Effect of irradiation time on the ultrasonic degradation of aqueous native dextran [2% w/v 60 W 30°C 20 kHz).

A 4 Arond, L. M., and H. P. Frank Molecular weight, molecular weight distribution and molecular size of a native dextran. J. Phys. Chem. 58, 953 (1954). 

E 2 — tlber extrem grofie Makromolekiile IV. Ultrazentrifugen- und Diffusions messungen an nicht-Newtonschen Losungen nativer Dextrane. Makromol. Chem. 33, 166 (1959). 

Figure 1 shows tablets (300 mg) of native dextran obtained from Leuconostoc mesenteroides B-512F (Sigma) with a 10% water (w/w) punch in an eccentric machine (Manesty) at 15 kN with tablet side (flat-flace diameter) 10mm. Axial displacement of water was observed according to the change in color. 

FIGURE 1 Native dextran tablet press in eccentric machine shows variability of color due to different pressure between upper and lower punches. 

Natural products can be used as plant extracts with pharmacological activity (e.g., Mangifera indica L., vallerian, aloe, Cratoxylum pruniflorum, microporous zeolite), excipient for direct compression or granulation (chitin, chitosan, and dextran), and controlled-release systems (cellulose and native dextran). For natural products the most important factor is the standardization of the extract because properties such as the amount of active substance can be changed from batch to batch. Factors such as the origin of the extract, geographic zone, and age of the tree could affect the properties of natural extracts. 

Figure 20 shows dissolution profiles for tablets of PPL or LBZ from the native dextran DTB110-1-2 matrix system, respectively 1 1 (w/w). The value for relative standard deviation (CV) was less than 5% for all points measured (n = 12). 

Note cEx-PPL, ratio of excipients to propranolol DT-HPMC, ratio of native dextran to hydroxypro-pylmethylcellulose ce, percentage of cetyl alcohol (w/w) in the tablets. Time f100% is time (hours) when 100% of PPL is dissolved in dissolution medium and f3CI% is time (hours) when 30% of PPL is dissolved in dissolution medium t2 is percent of PPL dissolved at 4h, tz percent of PPL dissolved at 8h, and t4 percent of PPL dissolved at 14h. Values presented are the average of eighteen replicates for each batch. Inside the USP range. Outside USP range. 

Castellanos Gil, E., Bataille, B., Iraizoz Colarte, A., Delarbre, J. L., El Ghzaoui, A., and Durand, D. (2008), A sugar cane native dextran as an innovative functional excipient for the development of pharmaceutical tablets. Eur. J. Pharm. Biopharm 68 (2), 319-329. 

Jeanes and her collaborators were the first to make a systematic investigation of the specific rotations of the native dextrans derived from 96 different strains of bacteria. They obtained a rough correlation between [a] n (in formamide) and the content of (1 3)-like linkages present in the... 

For use as a blood-plasma substitute, the dextran should have a molecular weight in the range of 50,000 to 100,000. This criterion has occasioned a concerted effort to produce dextrans in the correct range. Partial, acid hydrolysis of native dextran followed by fractionation with various solvents, or enzymic production of dextran of low molecular weight are methods which have been used. In addition, ultrasonics has been suggested as a means of depolymerizating native dextran to the correct size for clinical use. Introduction of alternative acceptors into the reaction mixture for enzymic synthesis has also been employed for this purpose it is described in an earlier Section of this Chapter. 

The degree of precipitation with the synthetic linear dextran as compared with the usual native dextrans has been of value in examining anti-dextrans produced in humans, - and in rabbits - and has shown that the heterogeneous populations of antidextran may be mixtures of molecules with specificities directed toward internal chains of a-(1 6) linked residues as well as those with specificities directed toward terminal nonreducing ends of chains. Fractions of such antibodies separated by isoelectric focusing were found to differ in the proportions of their antibodies precipitable by the synthetic linear dextran. 

The irradiation of dextran in the solid state and in solution has been studied in detail. When dry, native dextran of high molecular weight (from Leuconoatoc mesenteroides) is irradiated with 800 KV peak electrons, the initial, molecular weight amounting to several million is diminished to about... 

Fujimoto and coworkers determined that the order of stabilities to acid hydrolysis of D-glucopyranosidic linkages is reversed under the conditions of acetolysis this may be due to steric factors affecting the acetylium ion. In consequence, acetolytic, degradative procedures have enabled secondary-linked disaccharide fragments to be obtained from a large number of native dextrans. The o-D-linked disaccharides obtained by acetolysis and deacetylation of a cross-section of dextrans are listed in Table II. The results may be seen to complement data from periodate... 

NRRL B-742 dextran may be artifactual structures, resulting from incomplete methylation of this highly branched polysaccharide. Dextrans have been methylated most frequently by the Haworth method, " and by procedures that employ sodium and methyl iodide in liquid ammonia. " " Rapid methylation of dextrans has been achieved " through the use of the Hakomori procedure, which utilizes methyl sulfoxide as solvent for the dextran. Careful control of the reaction temperature would, however, appear to be essential when a dextran is methylated in this solvent, as hot methyl sulfoxide has been reported to depolymerize native dextrans." ... 

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