Analogues of the Potent Nonpolyglutamatable Antifolate Nα-(4-Amino-4-deoxypteroyl)-Nδ-hemiphthaloyl-l-ornithine (PT523) with Modifications in the Side Chain, p-Aminobenzoyl Moiety, or 9,10-Bridge: Synthesis and in Vitro Antitumor Activity

Seven Nα-(4-amino-4-deoxypteroyl)-Nδ-hemiphthaloyl-l-ornithine (2, PT523) analogues were synthesized by modifications of the literature synthesis of the corresponding AMT (1) analogues and were tested as inhibitors of tumor cell growth. In growth assays against cultured CCRF-CEM human leukemic cells exposed to drug for 72 h, the IC50 values of analogues in which N10 was replaced by CH2 and CHMe were found to be 0.55 ± 0.07 and 0.63 ± 0.08 nM, and thus these analogues are more potent than 1 (IC50 = 4.4 ± 1.0 nM) or 2 (IC50 = 1.5 ± 0.39 nM). The 10-ethyl-10-deaza analogue of 2 (IC50 = 1.2 ± 0.25 nM) was not statistically different from 2 but was more potent than edatrexate, the 10-ethyl-10-deaza analogue of 1, which had an IC50 of 3.3 ± 0.36 nM. In contrast, the analogue of 2 with both an ethyl and a CO2Me group at the 10-position had an IC50 of 54 ± 4.9 nM, showing this modification to be unfavorable. The 4-amino-1-naphthoic acid analogue of 2 had an IC50 of 1.2 ± 0.22 nM, indicating that replacement of th...