Synthesis and antifolate properties of 9-alkyl-10-deazaminopterins

A Ball-Milling-Enabled Reformatsky Reaction

An operationally simple one-jar one-step mechanochemical Reformatsky reaction using in situ generated organozinc intermediates under neat grinding conditions has been developed. Notable features of this reaction protocol are that it requires no solvent, no inert gases, and no pre-activation of the bulk zinc source. The developed process is demonstrated to have good substrate scope (39-82 % yield) and is effective irrespective of the initial morphology of the zinc source.

Novel 5-substituted, 2,4-diaminofuro[2,3-d]pyrimidines as multireceptor tyrosine kinase and dihydrofolate reductase inhibitors with antiangiogenic and antitumor activity

Recent evidence suggests that combination therapy of cancer with receptor tyrosine kinase (RTK) inhibitors, which are usually cytostatic, with conventional chemotherapeutic agents, which are usually cytotoxic, provide an improved treatment option. We have designed, synthesized, and evaluated a series of novel 2,4-diamino-5-substituted furo[2,3-d]pyrimidines with RTK and dihydrofolate reductase (DHFR) inhibitory activity in single molecules, as potential cytostatic and cytotoxic agents with antitumor activity. These compounds were synthesized from 2,4-diamino-5-chloromethyl furo[2,3-d]pyrimidine and aryl methyl ketones using the Wittig reaction to afford the C-8-C-9 unsaturated analogs followed by catalytic reduction to the corresponding saturated compounds. The saturated and unsaturated C-8-C-9 bridged compounds were evaluated as inhibitors of vascular endothelial growth factor receptor (VEGFR-2, Flk, KDR), epidermal growth factor receptor, and platelet-derived growth factor receptor-beta (PDGFR-beta). Selected analogs were also evaluated as antiangiogenic agents in the chicken embryo chorioallantoic membrane (CAM) assay. The compounds were also evaluated as inhibitors of human (h) DHFR and Toxoplasma gondii (tg) DHFR. In each evaluation, a known standard compound was used as a comparison. Of the compounds evaluated, compound 32 was as potent as the standard compounds against VEGFR-2 and PDGFR-beta, showing dual inhibitory activity against RTK. This analog was also highly effective in the CAM assay. A second analog 18 also demonstrated dual VEGFR-2 and PDGFR-beta inhibitory activity as well as potent antiangiogenic activity in the CAM assay. Four additional analogs were also effective against PDGFR-beta and in the CAM assay. An unsaturated C-8-C-9 moiety was necessary for RTK inhibitory activity. Compound 32 also showed inhibitory activity against hDHFR and tgDHFR, illustrating the multitarget inhibitory potential of these analogs. The biological activity of these analogs also suggests the necessity of an unsaturated C-8-C-9 bridge for dual RTK and DHFR inhibitory activity. Compounds 18 and 32 were also evaluated in a B16 melanoma mouse model and were found to be more active as antitumor agents than methotrexate. In addition, both 18 and 32 were also active in decreasing lung metastases in a mouse model of B16 melanomas.

Effects of the substitution of Phe4 in the opioid peptide [D-Ala8]dynorphin A-(1-11)NH2

Phenylalanine at position 4 of the peptide dynorphin A (Dyn A) is an important residue for opioid receptor affinity and activity, but there is very little information available on the structure-activity relationships or conformational preference of this residue for interaction with kappa-opioid receptors. Based on the hypothesis that the spatial orientation of the aromatic ring at position 4 of Dyn A is important for opioid receptor affinity and selectivity, a series of Dyn A analogues with various Phe derivatives substituted at position 4 were synthesized and evaluated for their opioid receptor affinity and activity. The L- and D-Homophe4 (homophenylalanine) analogues of [D-Ala8]Dyn A-(1-11)NH2 were compared to the (R)- and (S)-Atc4 (2-aminotetralin-2-carboxylic acid) derivatives (Aldrich et al. Chirality 2001, 13, 125-129). [l-Homophe4,D-Ala8]Dyn A-(1-11)NH2 exhibited higher kappa-opioid receptor affinity than the D-Homophe4 isomer, while [(R)-Atc4,D-Ala8]Dyn A-(1-11)NH2 exhibited higher kappa-opioid receptor affinity than the (S)-Atc4 isomer. Comparing the structure of Atc to those of Phe and Homophe, these results suggest that the Atc isomers are functioning more as constrained Homophe rather than Phe analogues in these Dyn A derivatives. The higher kappa-opioid receptor affinity of the (R)-Atc4 analogue suggests that Phe4 of Dyn A most likely adopts a gauche (-) or trans conformation in the kappa-opioid receptor binding site. Comparison of [D-Ala8]Dyn A-(1-11)NH2 derivatives containing Aic4 (2-aminoindan-2-carboxylic acid) and Tic4 (1,2,3,4-tetrahydroisoquinoline-3-carboxylic acid) with the peptides containing their acyclic counterparts alpha-MePhe4 and N-MePhe4, respectively, suggest that the loss in opioid receptor affinity seen for the Aic4 and Tic4 analogues is probably due to an improper orientation of the aromatic ring in these residues. Most of the analogues in this series showed much lower affinity for delta-opioid receptors than the parent peptide, suggesting that kappa- and delta-opioid receptors have distinct binding pockets for the residue at position 4 of Dyn A. All of the analogues with high affinity for kappa-opioid receptors exhibited full agonist activity in the adenylyl cyclase assay using cloned kappa-opioid receptors, indicating that changes in the position or orientation of the phenyl ring in this residue did not alter the ability of the peptides to activate the receptor.

Interaction energy analyses of folate analog binding to human dihydrofolate reductase: contribution of the antifolate substructural regions to complex stability

The three-dimensional structure of the human dihydrofolate reductase (DHFR), methotrexate tetrazole, and NADPH ternary complex was used to model the corresponding ternary complexes with methotrexate tetrazole replaced by methotrexate, methotrexate-polyglutamate with three glutamyl residues, and 5,10-deazaaminopterin, respectively. Each complex was solvated in a 60-angstrom cube of explicit water and subjected to structural minimization followed by interaction energy analyses. Interaction energy calculations were performed for the antifolate interaction with water, NADPH, the DHFR binding site residues, the entire DHFR protein, and the solvated NADPH:DHFR complex. These studies revealed that methotrexate-polyglutamate exhibited the most stable interactions and that approximately one half of antifolate:DHFR stability could be accounted for by the interaction of the antifolate with the binding site residues. The antifolate structures were also subdivided into heterocyclic, phenyl, and glutamyl substructural regions. Interaction energies were subsequently calculated for the interactions of the subregions with water, NADPH, the DHFR binding site residues, the DHFR protein, and the solvated NADPH:DHFR complex. The glutamyl substructural region showed the greatest contribution to overall antifolate binding stability due to its interaction with the DHFR protein. The heterocyclic and phenyl substructural regions generally showed much less stable interactions. These results suggest that the primary stabilizing factor of the antifolate interaction is the interaction of glutamyl with the DHFR protein. Additionally, interaction energy analyses were performed for specific groups of atoms within the substructural regions. These studies indicated that the stability of the glutamyl interaction is due to the interaction of glutamyl oxygen atoms with the DHFR protein. In the case of the methotrexate tetrazole complex, the tetrazole nitrogens also contribute significantly to the stability of the glutamyl interaction. The carbon atoms of the heterocyclic and phenyl groups both showed more stable interactions with NADPH than with water, while the nitrogen atoms showed more stable interactions with water than with NADPH. Collectively, these results indicate that the glutamyl region is the most important in antifolate binding stability.

2,4-diamino-5-deaza-6-substituted pyrido[2,3-d]pyrimidine antifolates as potent and selective nonclassical inhibitors of dihydrofolate reductases

Fifteen novel nonclassical and two classical 2,4-diamino-6-(benzylamino)pyrido[2,3-d]pyrimidine antifolates were synthesized as potential inhibitors of Pneumocystis carinii, (pc) Toxoplasma gondii, (tg) rat liver (rl), and human (h) recombinant dihydrofolate reductases (DHFR). These analogues lack a 5-methyl substitution which has been shown to be important for increased hDHFR inhibitory activity. In addition, they contain a reversal of the C9-N10 bridge present in folates and most antifolates. The synthesis of the compounds involved the reaction of 2,4,6-triaminopyrimidine with the sodium salt of nitromalonaldehyde to afford the key intermediate 2,4-diamino-6-nitropyrido[2,3-d]pyrimidine (7), in a single step. Reduction of 7 to the 2,4,6-triaminopyrido[2,3-d]pyrimidine (8), followed by reductive amination with the appropriate benzaldehydes or phenylacetaldehydes afforded the target compounds. N9 methylation of these analogues was carried out using formaldehyde and sodium cyanoborohydride. The analogues demonstrated significant inhibition of pcDHFR and tgDHFR. N9 methylation significantly increased DHFR inhibitory potency. Compound 11, the 3'4'5'-trimethoxy-substituted analogue with a selectivity ratio of 9.4 for tgDHFR (compared to rlDHFR) was the most selective analogue of the nonclassical series. Compound 22, the N9 methyl 2'5'-dimethoxy-substituted analogue was the most potent analogue against tgDHFR (IC 50 = 6.3 nM) and was the second most selective analogue for tgDHFR (compared to rlDHFR) in the nonclassical series. The naphthyl-substituted analogues 23-25 were generally more potent against rlDHFR than against pcDHFR and tgDHFR. Selected analogues were also evaluated against Streptococcus faecium (sf) DHFR, Escherichia coli (ec) DHFR, Lactobacillus casei (lc) DHFR and tgDHFR with hDHFR as the mammalian reference, under slightly different assay conditions than those employed for rlDHFR. Analogues 11 and 22 had selectivity ratios of greater than 100 for tgDHFR (compared to hDHFR). Analogue 22 in particular, was the most selective analogue of the nonclassical series against tgDHFR (selectivity ratio = 303.5) with excellent potency (28 nM). Analogue 11, also displayed significant selectivity for sfDHFR (selectivity ratio = 4902). Compound 22 was evaluated in vivo for the inhibition of the growth of T.gondii trophozoites in mice, where at 50 mg/kg orally, it demonstrated distinct prolongation of survival without toxicity. Compounds 11, 12 and 21-23 were evaluated as antitumor agents in the National Cancer Institutes preclinical in vitro screening program. Compounds 12, 22, and 23 showed GI50s for tumor growth inhibition in the 10 -6 - 10 -7 M range.