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Highlights d Inhibitors of SARM1 NADase recapitulate SARM1 À/À phenotype and protect injured axons d Transient mitochondrial injury generates an intermediate state of axonal damage d Axons entering the intermediate state of damage are fated to subsequent degeneration d SARM1 inhibitors allow recovery of axons already in the intermediate injury state

Classical antifolate analogues containing a novel furo[2,3-d]pyrimidine ring system which include N-[4-[N-[(2,4-diaminofuro[2,3-d]pyrimidin-5- yl)methyl]amino]benzoyl]-L-glutamic acid (1) and its N-9 methyl analogue 2 were synthesized as potential dual inhibitors of thymidylate synthase (TS) and dihydrofolate reductase (DHFR) and as antitumor agents. Four nonclassical antifolates, 2,4-diamino-5-(anilinomethyl)furo[2,3-d]pyrimidines 3-6 with 3,4,5-trimethoxy, 3,4,5-trichloro, 3,4-dichloro, and 2,5-dimethoxy substituents, respectively, in the phenyl ring, were also synthesized as potential inhibitors of DHFRs including those from Pneumocystis carinii and Toxoplasma gondii, which are organisms responsible for opportunistic infections in AIDS patients. The classical and nonclassical analogues were obtained via nucleophilic displacements of the key intermediate 2,4-diamino-5-(chloromethyl)furo[2,3-d]pyrimidine with the appropriate (p-aminobenzoyl)-L-glutamate or substituted aniline. The key intermediate was in turn synthesized from 2,4-diamino-6-hydroxypyrimidine and 1,3-dichloroacetone. The final compounds were tested in vitro against rat liver, (recombinant) human, P. carinii, T. gondii, and Lactobacillus casei DHFRs. The classical analogues showed moderate to good DHFR inhibitory activity (IC50 10(-6)-10(-8) M) with the N-CH3 analogue 2 about twice as potent as 1. The nonclassical analogues were inactive with IC50S > 3 x 10(-5) M. The classical analogues were also evaluated as inhibitors of TS (L. casei, (recombinant) human and human CCRF-CEM), glycinamide ribonucleotide formyltransferase, and 5-aminoimidazole-4-carboxamide ribonucleotide formyltransferase and were found to be inactive against these enzymes. The classical analogues (particularly 2) were significantly cytotoxic toward a variety of tumor cell lines in culture. The nonclassical analogues were marginally active. Both classical compounds were good substrates for human folylpolyglutamate synthetase. Further evaluation of the cytotoxicity of 1 and 2 in CCRF-CEM cells and its sublines, having defined mechanisms of methotrexate (MTX) resistance, demonstrated that the analogues utilize the reduced folate/MTX-transport system and primarily inhibit DHFR and that poly-gamma-glutamylation was crucial to their mechanism of action. Protection studies in the FaDu squamous cell carcinoma cell line indicated that inhibition was completely reversed by leucovorin or the combination of thymidine plus hypoxanthine. Furthermore, for compounds 1 and 2, in contrast to MTX, the FaDu cells were better protected by thymidine alone than hypoxanthine alone, suggesting a predominantly antithymidylate effect.

Classical antifolate inhibitors of thymidylate synthase (TS) often require the reduced folate uptake system in order to exert their antitumor effects. In addition, these analogues are polyglutamylated via the enzyme folylpoly-gamma-glutamate synthetase (FPGS), which prevents analogue efflux from the cell and usually increases their inhibitory potency against TS. Impaired function of the reduced folate uptake system and that of FPGS are potential sources of resistance to such antifolates. We designed and synthesized a classical 6-5 ring-fused analogue N-[4-[(2-amino-6-methyl-3,4-dihydro-4-oxo-7H-pyrrolo[2,3- d]pyrimidin-5-yl)thio]-benzoyl]-L-glutamic acid (5) and a nonclassical 6-5 ring-fused analogue 2-amino-6-methyl-5-(pyridin-4-ylthio)-3,4-dihydro-4-oxo-7H-pyrrolo [2,3- d]pyrimidine (6) as TS inhibitors and antitumor agents. The syntheses of analogues 5 and 6 were achieved via the oxidative addition of the sodium salt of ethyl 4-mercaptobenzoate or 4-mercaptopyridine to 2-(pivaloylamino)-6-methyl-3,4-dihydro-4-oxo-7H-pyrrolo[2,3-d]pyri midine (17) in the presence of iodine. For the synthesis of 5 the ester obtained from the reaction was deprotected and coupled with diethyl L-glutamate followed by saponification. Compound 5 was a potent inhibitor of human and bacterial TS with IC50 values of 42 and 21 nM, respectively. Compound 6 was 10-fold less potent than 5 against human TS but more than 4700-fold less potent than 5 against Lactobacillus casei TS. The classical analogue 5 was neither a substrate nor an inhibitor of human FPGS derived from CCRF-CEM cells. Compound 5 was cytotoxic to CCRF-CEM and FaDu tumor cell lines as well as to an FPGS-deficient subline of CCRF-CEM. Thymidine protection studies established that TS was the primary target of 5.