SOLID-PHASE SYNTHESIS OF POLYGLUTAMATES OF FOLIC ACID

Details of an unambiguous chemical synthesis by which pteroy 1-(γ-L-glutamyl)n-L-glutamic acid of any desired chain length (up to = 6) may be prepared are reported. The proceduresemployed are modifications of the Merrifield solid-phase peptide synthetic system. Glutamic acid was attached to the resin by esterification of t-butyloxycarbonyl-L-glutamic acid ct-benzyl ester (I)to the benzyl chloride groups on the resin. Deprotection was carried out by treatment for 30 min with 20% v/v trifluoroacetic acid in methylene chloride at room temperature. Peptide formationwas accomplished by reaction of the mixed anhydride of I and isobutyl formate with the amino-deprotected aminoacyl-resin. After cycles of deprotection and coupling to the desired chain length, the peptide was terminated by coupling N-2,N-10-bis(trifluoroacetyl)- pteroic acid (II). The mixed anhydride of II and isobutyl formate was used for the peptide formation. The synthesis of II is described. Cleavage of the product from the resin was carried out by gassing the resin-bound product suspended in trifluoroacetic acid with HBr. Deprotection of the cleaved product was carried outin 0.5 nNaOH under N2, after removal of the trifluoroacetic acid. Details of the chromatographicbehavior and biological activity of the products are reported. © 1969, American Chemical Society. All rights reserved.