| SYNTHESIS |
SYNTHESIS OF POLY(N-BENZOYL-L-GLUTAMIC ACID) (1) Introduction: The synthesis of Poly(N-benzoyl-L-glutamic acid) (PBGA) requires three steps: (i) blocking the amino group; (ii) forming the mixed anhydrides of N-benzoyl-L-glutamic acid (BGA) and acetic acid: and (iii) polymerization. These three steps are used in any class of polyanhydrides. (2) Synthesis of Mixed Anhydride Prepolymer: The mixed anhydride of BGA and acetic acid is a prepolymer for the polymerization step. It is prepared by the method of Conix which was used in the prototype synthesis of PCPM. In a trial run, BGA (200 mg) was refluxed in excess acetic anhydride (10 ml) at 152.degree. C. for 51/2 hours. BGA dissolved quickly in the warm acetic anhydride to form a clear solution. The reaction mixture turned yellow and then brownish yellow as the reaction proceeded. A brownish solid was recovered by reducing the reaction mixture to an oil and adding petroleum ether. The yield was 50% of theoretical. An IR spectra of the mixed anhydride would be expected to show a characteristic carbonyl doublet for the anhydride at 1820 cm.sup.-1 and 1760 cm.sup.-1. A characteristic band should also be present at 1650 cm.sup.-1 due to the amide carbonyl. An IR spectra of the brownish solid prepolymer showed bands at 1830 cm.sup.-1, 1750 cm.sup.-1 and 1650 cm.sup.-1. Therefore, the agreement between the predicted spectra and the actual spectra of the brownish solid prepolymer and the absence of the band associates with the hydroxyl group positively identified the solid material as the mixed anhydride. ##STR9## Two other general procedures exist for synthesizing anhydrides which may be adaptable to preparing BGA, acetic acid mixed anhydrides. Both procedures used stoichiometric quantities of reactants so dimer and cyclic anhydride formation should be reduced. The first of these procedures involves the addition of acetyl chloride to pyridine in benzene with stirring. To this mixture, BGA would be added resulting in the formation of prepolymer. This procedure is an adaptation of the preparation of heptanoic anhydride from heptanoic acid and heptanoyl chloride. The second procedure involves adding acetyl chloride dropwise to a stirred suspension of the disodium salt of BGA suspended in benzene. After the reaction is complete the mixture would be filtered and concentrated. This method has been used to prepare phenylacetic anhydride from phenylacetylchloride and sodium phenylacetate. |
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