Natural Products Including Naturally Occurring Polymers and Derivatives

NATURAL PRODUCTS INCLUDING NATURALLY OCCURRING POLYMERS AND DERIVATIVES 

Albumin, gelatin (43), deoxycholic acid, sesame oil (44), and gangliosides (45,46) are substances that occur naturally in the body, and hence these would be exquisitely suited as excipients. 

Histones are highly basic, small, compact proteins, with a high affinity for DNA. They occur naturally, attached to the DNA of cell nuclei by ionic linkages. Their classification is based on the relative amounts of lysine and arginine. The galactosylated, lysine-rich histone HI was found to be superior to the H2-H4 histones as a DNA carrier for liver gene delivery (53). 

Heparin and heparin-like polyanions are known to have significant stabilizing effects on proteins. Heparin itself has been used as a constituent of the solution used to reconstitute lyophilized proteins (54) while enoxaparin is a low molecular weight 

Bacterial pore-forming proteins, such as oc-hemolysin, secreted by Staphylococcus aureus can be modified so that pore formation is activated by chemical, biochemical, or physical triggers. Such hemolysins, when targeted to tumors, could increase tumor permeability, and hence susceptibility to various cytotoxic drugs (78). 

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Table 2 Natural Products Including Naturally Occurring Polymers and Derivatives...

Amylopectins. — The effects of acrylamide graft copolymerization on the solution properties of amylopectin have been discussed. Amylopectin has been dyed with DyAmyl-L and used in this form as a substrate for the assay of a-amylase. Amylopectin has been treated with isocyanate derivatives of 4-amino-( 1,1-dimethyl ethyl)-3-(methylthio)-l,2,4-triazin-5(4/f)-one ( metribuzin ) or acid chloride derivatives of 2,4-dichlorophenoxyacetic acid ( 2,4-D ) and 2,2-dichloropropionic acid ( dalapon ), to produce controlled-release polymeric pesticide systems. The solvent system utilized for these reactions, a lithium chloride or bromide salt in AW-dimethylacetamide, allows dissolution of the reactant salt and facilitates analysis of the polymer product by such techniques as i.r., U.V., and n.m.r. spectroscopies and gel permeation chromatography. Derivatives of other naturally occurring polysaccharides, including amylopectin, cellulose, chitin, and dextran, were also prepared. 

Many drop stabilizers in suspension polymerization are water-miscible polymers. These materials are sometimes called protective colloids. They include naturally occurring substances, such as gelatin and pectin, and a wide range of synthetic polymers such as partially hydrolyzed poly(vinyl acetate)s. Modified natural products such as cellulose ether derivatives are also widely used. Munzer and Trommsdorff provide a detailed list of patented stabilizers [1]. Polymeric stabilizers do not all act in the same way but steric effects are often important [16]. Although transfer of stabilizer molecules from the continuous phase to the drop surfaces can sometimes be fast, the development of drop stability may be slow [17]. That may arise because rearrangement of stabilizer molecules on the drop surface is necessary. Water-miscible polymers are not expected to be good drop stabilizers when the continuous phase is nonaqueous (see Section 5.5). 

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