The invention claimed herein relates to an improvement in a process for synthesizing a compound of formula Ib:wherein R1 and R2 are each individually amino or N-alkyl substituted amino; hydroxy; alkoxy; keto; lower alkyl; or a nitrogen or oxygen protecting group;R3 is hydrogen; hydroxy; alkoxy; trifluoromethyl alkoxy; halo; sulfhydryl or alkylthio;R4 is —C(O)—X;X is hydroxy; alkoxy; or an amino acid residue;in which process a 2-amino-5-nitro-benzonitrile starting reagent is cyclized to form 2,4-diamino-6-nitro-quinazoline, which is converted to 2,4,6-triamino-quinazoline, which is converted to 2,4-diamino-6-cyano-quinazoline, which is converted to 2,4-diamino-6-formyl-quinazoline;in which the improvement includes:reacting an R4-p-benzoic acid alkylene moiety with triethyl phosphite to form a 4-R4-carbonyloxyalkyl-phenyl-alkyldiethylphosphite; andreacting the 2,4-diamino-6-formyl-quinazoline with the 4-R4-carbonyloxyalkyl-phenyl-alkyldiethylphosphite to form the compound of formula Ib.