Novel synthesis of 8-deaza-5,6,7,8-tetrahydroaminopterin analogues via an aziridine intermediate

An efficient method for the construction of the tetrahydrofolate skeleton is described. Starting from pterin analogues and aromatic amines, 8-deaza-5,6,7,8-tetrahydroaminopterin derivatives and the heterocyclic benzoyl isosteres were synthesized via a novel aziridine intermediate. Following this method, the byproducts of carbon-nitrogen bond hydrogenolysis in traditional synthetic strategy can be completely avoided.

Pralatrexate, a dihydrofolate reductase inhibitor for the potential treatment of several malignancies

Pralatrexate, a 10-deazaaminopterin derivative, is being developed by Allos Therapeutics Inc for the potential treatment of malignancies. The folate analog inhibits dihydrofolate reductase and was developed to overcome the limitations of the folate analog methotrexate. Compared with methotrexate in preclinical studies, pralatrexate demonstrated superior intracellular transport via the reduced folate carrier, and increased accumulation within cells by enhanced polyglutamylation. Preclinical studies in vitro and in models of B-cell lymphomas, T-cell lymphomas and NSCLC indicated that pralatrexate exhibited antitumor activity that was superior to the activity of other antifolates. In phase I clinical trials, the DLT for pralatrexate was mucositis, which could be abrogated with folic acid and vitamin B12 supplementation. The administration of pralatrexate to patients with T-cell lymphomas and NSCLC resulted in significant tumor remissions. At the time of publication, pralatrexate was in phase II clinical trials for the treatment of peripheral T-cell lymphoma, a phase I/II trial in combination with gemcitabine for the treatment of non-Hodgkin's lymphoma, and a phase IIb trial in comparison with erlotinib in patients with NSCLC. Because of the limited therapies available for peripheral T-cell lymphoma, pralatrexate could have a secure niche for the treatment of this indication, if ongoing clinical trials and future phase III trials confirm the efficacy of the drug. In contrast, for pralatrexate to be incorporated into the accepted treatment options for NSCLC, the drug will need to prove clear superiority to established agents.

Prodrug forms of N-[(4-deoxy-4-amino-10-methyl)pteroyl]glutamate-gamma-[psiP(O)(OH)]-glutarate, a potent inhibitor of folylpoly-gamma-glutamate synthetase: synthesis and hydrolytic stability

Ester prodrugs of the phosphinate pseudopeptide N-[(4-deoxy-4-amino-10-methyl)pteroyl]glutamate-gamma-[psiP(O)(OH)]-glutarate (1a) were synthesized. H-phosphinic acids derived from N-Cbz vinyl glycine esters were converted to the desired pseudopeptides by Michael addition to alpha-methyleneglutarate esters. Pivaloyloxymethyl (POM) ester moieties were incorporated in both the N-terminal and C-terminal fragments prior to formation of either C-P bond. N-Alkylation of the corresponding amides derived from p-(N-methyl)aminobenzoic acid with 2,4-diamino-6-(bromomethyl)pteridine gave the target compounds. POM esters of methotrexate and the corresponding gamma-glutamyl conjugate were also synthesized using the same strategy. All prodrugs were evaluated in Chinese hamster ovary cells. Although the pseudopeptide prodrugs were ineffective, prodrugs of methotrexate and the corresponding gamma-glutamyl conjugate were equipotent with the parent compounds. Stability of the prodrugs was investigated in both phosphate buffer and cell line medium to provide a rationale for the observed biological data.

Synthesis and in Vitro Antifolate Activity of Rotationally Restricted Aminopterin and Methotrexate Analogues

Heretofore unknown analogues of aminopterin (AMT) and methotrexate (MTX) in which free rotation of the amide bond between the phenyl ring and amino acid side chain is prevented by a CH(2) bridge were synthesized and tested for in vitro antifolate activity. The K(i) of the AMT analogue (9) against human dihydrofolate reductase (DHFR) was 34 pM, whereas that of the MTX analogue (10) was 2100 pM. Both compounds were less potent than the parent drugs. However, although the difference between AMT and MTX was <2-fold, the difference between 9 and 10 was 62-fold, suggesting that the effect of N(10)-methyl substitution is amplified in the bridged compounds. The K(i) values of 9 and 10 as inhibitors of [(3)H]MTX influx into CCRF-CEM human leukemia cells via the reduced folate carrier (RFC) were 0.28 and 1.1 muM, respectively. The corresponding K(i) and K(t) values determined earlier for AMT and MTX were 5.4 and 4.7 muM, respectively. Thus, in contrast to its unfavorable effect on DHFR binding, the CH(2) bridge increased RFC binding. In a 72 h growth assay with CCRF-CEM cells, the IC(50) values of 9 and 10 were 5.1 and 140 nM, respectively, a 27-fold difference that was qualitatively consistent with the observed combination of weaker DHFR binding and stronger RFC binding. Although rotationally restricted inhibitors of other enzymes of folate pathway enzymes have been described previously, 9 and 10 are the first reported examples of DHFR inhibitors of this type.

Analogues of methotrexate in rheumatoid arthritis. 2. Effects of 5-deazaaminopterin, 5,10-dideazaaminopterin, and analogues on type II collagen-induced arthritis in mice

Twenty-six compounds derived from the 5-deaza- and 5,10-dideazaaminopterin series of aminopterin analogues were evaluated for antiarthritic activity in the mouse type II collagen model. New compounds in the 5-deaza series were prepared by alkylation of an appropriate N-substituted (4-aminobenzoyl)-L-glutamic acid dialkyl ester or N-(5-amino-2-thenoyl)-L-glutamate diester with a 2,4-diamino-5-alkyl-6-(bromomethyl)-5-deazapteridine. The resultant 5-deazaaminopterin diesters were saponified to provide the target 5-deaza analogues. 5,10-Dideazaaminopterins were synthesized by similar alkylation of the carbanions of appropriate 4-carboxyphenylacetic, (5-carboxy-2-thienyl)acetic, or (5-carboxy-2-pyridyl)acetic acid dimethyl esters. The diesters of the 2,4-diamino-4-deoxy-10-carboxy-5,10-dideazapteroic acid types so obtained were saponified and then readily decarboxylated by heating in Me2SO solution to provide the 2,4-diamino-5,10-dideazapteroic acid-type intermediates. Peptide coupling with diethyl L-glutamate followed by ester hydrolysis at room temperature afforded the new 5,10-dideazaaminopterin analogues. 5-Deazaaminopterins bearing an alkyl substituent at the 5-position were generally quite effective as antiinflammatory agents. Thus 5-propyl-5-deazaaminopterin, 5-methyl-10-propargyl-5-deazaaminopterin, 5-methyl-10-allyl-5-deazaaminopterin, 5-ethyl-5-deazamethotrexate, and 2,5-disubstituted thiophene analogue of 5-methyl-5-deazaaminopterin showed potencies greater than methotrexate by intraperitoneal or oral administration and were active over a considerably broader dose range. Useful activity in the 5,10-dideaza series was only observed for 5,10-dideazaaminopterin and its 10-methyl analogue. Alkyl substitution at C-5 or C-10 was generally detrimental to antiinflammatory activity in this series.

Studies on the antitumor effects of analogues of 5,8-dideazaisofolic acid and 5,8-dideazaisoaminopterin

Six new analogues of 5,8-dideazaisofolic acid and 5,8-dideazaisoaminopterin were synthesized in an effort to obtain enhanced antitumor activity. The modifications included the replacement of the 2-amino group by hydrogen or methyl as well as the inclusion of a methyl substituent at position 9. Based upon activity against L1210 leukemia cells in culture, three of the new analogues together with one compound described previously were evaluated for cytotoxicity in vitro using three human tumor cell lines (Colo 320 DM, Hep G2 and HL-60). The most effective compound was 2-desamino-N9-methyl-5,8-dideazaisoaminopterin (2c) with the HL-60 cells being the most sensitive to its cytotoxic effects. These analogues were evaluated in vitro as inhibitors of dihydrofolate reductase (DHFR) and thymidylate synthase (TS) from human as well as bacterial (Lactobacillus casei) sources. All four of the 4-amino analogues were most effective toward L. casei DHFR compared with human DHFR, with 2-desamino-2-methyl-5,8-dideazaisoaminopterin (2d) and its 9-methyl derivative (2e) having 818- and 430-fold greater selectivity (L. casei/human). Most of the compounds studied were found to be only modest inhibitors of human TS (I50 values = 1.5 to 20 microM) and were therefore at least 40-fold less inhibitory than 10-propargyl-5,8-dideazafolic acid. Nevertheless, reversal of cytotoxicity studies with thymidine, hypoxanthine and folinic acid using the HL-60 cell line suggested that TS is the primary target for these analogues.

New thiophene substituted 10-deazaaminopterins: synthesis and biological evaluation

Analogues of 10-deazaaminopterin (10-DAM) and 4-amino-4-deoxy-10-deazapteroyl-gamma-methylene glutamic acid (MDAM) in which the benzene ring was replaced with a thiophene ring have been synthesized and evaluated for their antitumor activity. These analogues were N-([5-(2,4-diamino-6-pteridinyl)ethyl]-2-thenoyl)-L- glutamic acid (1) and N-([5-(2,4-diamino-6-pteridinyl)ethyl]-2-thenoyl)-gamma-meth ylene glutamic acid (2).

Synthesis and antifolate evaluation of 10-ethyl-5-methyl-5,10- dideazaaminopterin and an alternative synthesis of 10-ethyl-10- deazaaminopterin (edatrexate)

Previous findings suggesting that 5,10-dialkyl-substituted derivatives of 5,10-dideazaaminopterin warranted study as potential antifolates prompted synthesis of 10-ethyl-5-methyl-5,10- dideazaaminopterin (12a). The key step in the synthetic route to 12a was Wittig condensation of the tributylphosphorane derived from 6-(bromomethyl)-2,4-diamino-5-methylpyrido[2,3-d]pyrimidine (7a) with methyl 4-propionylbenzoate. Reaction conditions for the Wittig condensation were developed using the tributylphosphorane prepared from 6-(bromomethyl)-2,4-pteridinediamine (7b) as a model. Each of the respective Wittig products 8a and 8b was obtained in 75-80% yield. Hydrogenation of 8a and 8b at their 9,10-double bond afforded 4-amino-4-deoxy-10-ethyl-5-methyl-5,10-dideazapteroic acid methyl ester (9a) and 4-amino-4-deoxy-10-ethyl-10-deazapteroic acid methyl ester (9b). This route to 9b intersects reported synthetic approaches leading to 10-ethyl-10-deazaaminopterin (10-EDAM, edatrexate), an agent now in advanced clinical trials. Thus the Wittig approach affords an alternative synthetic route to 10-EDAM. Remaining steps were ester hydrolysis of 9a,b to give carboxylic acids 10a,b followed by standard peptide coupling with diethyl L-glutamate to produce diethyl esters 11a,b, which on hydrolysis gave 12a and 10-EDAM (12b), respectively. The relative influx of 12a was enhanced about 3.2-fold over MTX, but as an inhibitor of dihydrofolate reductase (DHFR) from L1210 cells and in the inhibition of L1210 cell growth in vitro, this compound was approximately 20-fold less effective than MTX (DHFR inhibition, Ki = 4.82 +/- 0.60 pM for MTX, 100 pM for 12a; cell growth, IC50 = 3.4 +/- 1.0 nM for MTX, 65 +/- 18 nM for 12a).

Synthesis and antifolate properties of 5,10-ethano-5,10-dideazaaminopterin

2-Carbomethoxy-4-(p-carbomethoxyphenyl)cyclohexanone was prepared in a four-step process and thermally condensed with 2,4,6-triaminopyrimidine to afford methyl 2,4-diamino-4-deoxy-7-hydroxy-5,10-ethano-5,10-dideazapteroate+ ++. Reduction of the 7-oxo function with borane gave the 7,8-dihydro pterin which was subsequently oxidized to the fully aromatic pteroate ester with dicyanodichlorobenzoquinone. Saponification of the benzoate ester, coupling with diethyl glutamate and final ester hydrolysis afforded the title compound. This novel deazaaminopterin analogue was approximately as potent as methotrexate in vitro in terms of DHFR and L1210 cell growth inhibition. There are indications of diastereomeric differences in the enzyme inhibition measurements. A significant transport advantage over MTX for influx into L1210 cells was observed. The compound was active against the E 0771 murine mammary solid tumor, but further investigation with individual diastereomers is required to define the ED50.

Synthesis and antifolate evaluation of the 10-propargyl derivatives of 5-deazafolic acid, 5-deazaaminopterin, and 5-methyl-5-deazaaminopterin

5-Deaza-10-propargylfolic acid (4), an analogue of the thymidylate synthase (TS) inhibitor 10-propargyl-5,8-dideazafolic acid (PDDF, 1), was prepared via alkylation of diethyl N-[4-(propargylamino)benzoyl]-L-glutamate (7) by 2-amino-6-(bromomethyl)-4(3H)-pyrido[2,3-d]pyrimidinone (15). Bromomethyl intermediate 15 was prepared from the corresponding hydroxymethyl precursor 14 by treatment with 48% HBr. Hydroxymethyl compound 14 was obtained by deamination of reported 2,4-diaminopyrido[2,3-d]pyrimidine-6-methanol (12a) in refluxing 1 N NaOH. Both 12a and its 5-methyl-substituted analogue 12b were converted to versatile 6-bromomethyl intermediates 13a and 13b from which important antifolates may be readily derived. Alkylation of 7 by 13a,b led to 10-propargyl-5-deazaaminopterin (5) and 5-methyl-10-propargyl-5-deazaaminopterin (6). As an inhibitor of TS from H35F/F cells, 4 gave an IC50 value showing it to be approximately 6-fold less inhibitory than PDDF (90 nM for 4 vs 14 nM for PDDF). In in vitro studies, IC50 (microM) values obtained for 4 vs L1210 and S180 of 1.50 and 2.35, respectively, were similar to those obtained for PDDF (2.61 and 1.97). Against HL60 cells, 4 was about 7-fold more cytotoxic than PDDF (IC50 values 0.72 and 5.29 microM). Inclusion of thymidine did not establish TS as the site of cytotoxic action for either 4 or PDDF in the cell lines used. In in vivo tests against L1210 in mice, 4 failed to show therapeutic effect. The 2,4-diamino compounds 5 and 6 were as potent inhibitors of DHFR from L1210 cells as MTX and 7- and 35-fold, respectively, more inhibitory than MTX toward L1210 cell growth. In mediated influx into L1210 cells, 5 and 6 were transported 2.7- and 8.5-fold, respectively, more readily than MTX. Against the EO771 mammary adenocarcinoma in mice, 6 produced greater antitumor effect than MTX. A dose of 36 mg/kg per day for 5 days caused no toxic deaths while the average tumor volume among 10 mice was reduced to 8-9% of that of the control, and 20% of the test animals were rendered tumor free.

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

Reformatski condensation of benzyl 2-bromopropionate with 4-carbomethoxybenzaldehyde, followed by dehydration afforded benzyl 2-methyl-p-carbomethoxycinnamate (4a). Hydrogenation over a Pd catalyst gave the hydrocinnamic acid 5a. Conversion to the chloromethyl (6a) and azidomethyl ketone (7a) was followed by hydrogenation to the aminomethyl ketone (8a). Direct N-alkylation by 2,4-diamino-5-nitro-6-chloropyrimidine followed by reductive ring closure in Zn-HOAc and subsequent saponification of the benzoate ester yielded 4-amino-4-deoxy-9-methyl-10-deazapteroic acid (11a). Coupling with diethyl L-glutamate and saponification afforded 9-methyl-10-deazaminopterin (13a). The 9-ethyl analogue (13b) was similarly prepared from benzyl 2-bromobutyrate. The 9-methyl analogue (13a) was 21 times more potent than MTX as an inhibitor of cell growth in L1210 cells. The reason for this enhanced cytotoxicity in L1210 is unclear, since enzyme inhibition and transport parameters were similar to those of MTX. In human Manca leukemia cells growth inhibition was not dramatic and paralleled MTX.

Chemical synthesis and biological activities of 5-deazaaminopterin analogues bearing substituent(s) at the 5- and/or 7-position(s)

Condensation of cyanothioacetamide (4) with ethyl alpha-(ethoxymethylene)acetoacetate (5b), ethyl 4-ethoxy-2-(ethoxymethylene)-3-oxobutanoate (5c), ethyl 2-(ethoxymethylene)-3-oxo-4-phenylpropanoate (5d) afforded exclusively the corresponding 6-substituted pyridines (6b-d). Cyclization of 4 with 3-carbethoxybutane-2,4-dione (5e) gave 3-cyano-5-(ethoxycarbonyl)-4,6-dimethylpyridine-2(1H)-thione (6e), whereas reaction of 4 with 3-carbethoxy-1-phenylpropane-1,3-dione (5f) yielded two products, 3-cyano-5-(ethoxycarbonyl)-4-methyl-6-phenylpyridine-2(1H)-thione (6f) and the 6-methyl-4-phenyl isomer 6g. The structural assignments for 6f and 6g are made on the basis of 1H and 13C NMR spectral analyses of the 2-(methylthio)nicotinates (7f,g) prepared from 6f and 6g by treatment with MeI/K2CO3. Nicotinates 7b,d-g were converted into their corresponding 2,4-diaminopyrido[2,3-d]pyrimidines 12b,d-g in five steps, via reduction, protection, oxidation, condensation with guanidine, and deprotection. The 7-mono- and 5,7-disubstituted-5-deazaaminopterins (1b,d-g) were prepared from the respective pyrido[2,3-d]pyrimidines 12b,d-g. Preliminary biological studies showed that 7-methyl and 5,7-dimethyl analogues (1b and 1e) were less active than methotrexate against human leukemic HL-60 and murine L-1210 cells in tissue culture. Compound 1e produced an ILS of 71% at 100 mg/kg per day X 5 (ip) in BDF mice inoculated ip with 10(6) L-1210 cells.

Synthesis of 5-chloro-5,8-dideaza analogues of folic acid and aminopterin targeted for colon adenocarcinoma

Several classical quinazoline analogues of folic acid bearing chloro or methyl substituents at position 5 were evaluated as inhibitors of the growth of four human gastrointestinal adenocarcinoma cell lines in vitro. The preparation of two of these, 5-chloro-5,8-dideazaisofolic acid, 1e, and 5-chloro-5,8-dideazaisoaminopterin, 2a, is reported for the first time. In addition, a new synthetic route to 5-chloro-5,8-dideazaaminopterin, 2b, is described. For compounds having a 2,4-diamino configuration, the presence of chlorine at position 5 afforded superior growth inhibitory potency. However, compound 1e was substantially less effective than its 5-methyl counterpart.

Synthesis and antifolate properties of 5,10-methylenetetrahydro-8,10-dideazaminopterin

The synthesis of the 5,10-methylene analogue of 5,6,7,8-tetrahydro-8,10-dideazaminopterin, a potential dual inhibitor of dihydrofolate reductase (DHFR) and thymidylate synthase (TS) enzymes, is described. The dimethyl ester of 10-carboxy-4-amino-4-deoxy-8,10-dideazapteroic acid was converted to the tetrahydro derivative by hydrogenation. Thermally induced cyclization of the 10-carbomethoxy and the 5-NH groups afforded the 5,10-carbonyl analogue. Reduction of the lactam with borane readily yielded the key 5,10-methylene-4-amino-4-deoxy-8,10-dideazatetrahydropteroic acid methyl ester. Saponification of the benzoate ester and coupling with L-glutamate concluded the synthesis. The title compound was a modest inhibitor of growth in folate-dependent bacteria. Streptococcus faecium and Lactobacillus casei, but inhibition of DHFR or TS derived from L. casei was poor. The compound was also a weak inhibitor of DHFR derived from L1210 murine leukemia and was a weak inhibitor of L1210 growth in culture.

Methotrexate analogues. 28. Synthesis and biological evaluation of new gamma-monoamides of aminopterin and methotrexate

Lipophilic gamma-monoamide derivatives of aminopterin (AMT) were synthesized in high overall yield from 4-amino-4-deoxy-N10-formylpteroic acid and gamma-N-tert-alkyl-, gamma-N-aralkyl-, or gamma-N-arylamides of alpha-benzyl L-glutamate via a modification of the mixed carboxylic-carbonic anhydride coupling method. Coupling was also accomplished with p-nitrophenyl 4-amino-4-deoxy-N10-formylpteroate. Compounds obtained in this manner included the gamma-tert-butylamide, gamma-(1-adamantylamide), gamma-benzylamide, gamma-(3,4-dichlorobenzylamide), gamma-(2,6-dichlorobenzylamide), gamma-anilide, gamma-(3,4-methylenedioxyanilide), and gamma-(3,4-dihydroxanilide) derivatives of AMT. Also prepared, from 4-amino-4-deoxy-N10-methylpteroic acid via diethyl phosphorocyanidate coupling, was the gamma-(3,4-methylenedioxyanilide) of MTX. The methylenedioxyanilides were cleaved smoothly to dihydroxyanilides with boron tris(trifluoroacetate) in trifluoroacetic acid. All the gamma-monoamides were tested as inhibitors of purified dihydrofolate reductase (DHFR) from murine L1210 leukemia cells and as inhibitors of the growth of wild-type L1210 cells and a subline (L1210/R81) with high-level resistance to MTX and AMT based mainly on a defect in drug uptake via active transport. Several compounds were also tested against human leukemic lymphoblasts (CEM cells) and a resistant subline (CEM/MTX) whose resistance is likewise based on uptake. The IC50 of the gamma-monoamides against DHFR was 1.5- to 5-fold higher than that of the parent acids, but the IC50 against cultured cells varied over a much broader range, suggesting that uptake and/or metabolism rather than DHFR binding are principal determinants of in vitro growth inhibitory activity for these compounds. gamma-N-Aryl and gamma-N-aralkyl derivatives appeared to be more potent than gamma-N-tert-alkyl derivatives. Where comparison could be made, AMT gamma-monoamides were more potent than MTX gamma-monoamides. Several of the gamma-monoamides showed potency comparable to that of the parent acid against wild-type L1210 and CEM cells; all of them were more potent than MTX against the L1210/R81 subline; and some of the AMT gamma-monoamides were also more potent than the parent acid against resistant CEM/MTX cells. As a group, however, the gamma-monoamides were considerably more active against the murine cells than against the human cells, suggesting that the former may take up the amides better or may be able to metabolize them more efficiently than the parent acids. All the gamma-monoamides were tested in vivo against L1210 leukemia in mice.(ABSTRACT TRUNCATED AT 400 WORDS)

Synthesis and biological activity of resolved C-10 diastereomers of 10-methyl- and 10-ethyl-10-deazaminopterin

Synthesis and evaluation of the antitumor drugs 10-methyl- and 10-ethyl-10-deazaminopterin (15a,b) were previously reported for the diastereomeric mixtures, lacking resolution at the C-10 position. In order to assess biological properties of the individual diastereomers, the C-10 isomers of 4-amino-4-deoxy-10-methyl- and 10-ethyl-10-deazapteroic acids (13a,b) were prepared by total synthesis. Coupling with L-glutamate afforded the appropriate diastereomers of the title compounds. Biochemical, transport, and cell growth inhibitory properties in L1210 cells and folate-dependent bacteria were measured. Differences were generally less than 2-fold between diastereomeric pairs, but a factor of 3 was noted for d,L-15b vs. l,L-15b in inhibition of DHFR from L1210 cells and in cytotoxicity toward L1210 cells. An in vivo comparison of the isomers of 15b with racemic compound against L1210 in mice did not show a significant efficacy difference (ILS) among the compounds. However, d,L-15b showed an acute toxicity about 2.5 times that of l,L-15b.

Synthesis of the antileukemic agents 5,10-dideazaaminopterin and 5,10-dideaza-5,6,7,8-tetrahydroaminopterin

Total syntheses from pyridine precursors of 5,10-dideazaaminopterin (1) and 5,10-dideaza-5,6,7,8-tetrahydroaminopterin (2) are described. These compounds exhibit significant in vivo activity against L1210 leukemia that is comparable to that observed with methotrexate.

Methotrexate analogues. 25. Chemical and biological studies on the gamma-tert-butyl esters of methotrexate and aminopterin

gamma-tert-Butylaminopterin (gamma-tBAMT), the first example of an aminopterin (AMT) gamma-monoester, was synthesized, and new routes to the known N10-methyl analogue gamma-tert-butyl methotrexate (gamma-tBMTX) were developed. The inhibitory effects of gamma-tBAMT on the activity of purified dihydrofolate reductase (DHFR) from L1210 murine leukemia cells, the growth of L1210 cells and CEM human leukemic lymphoblasts in suspension culture, and the growth of several lines of human squamous cell carcinoma of the head and neck in monolayer culture were compared with the effects of gamma-tBMTX and the parent acids AMT and methotrexate (MTX). Patterns of cross-resistance to gamma-tBAMT, gamma-tBMTX, and AMT among several MTX-resistant cell lines were examined. In vivo antitumor activities of gamma-tBAMT and gamma-tBMTX were compared in mice with L1210 leukemia. While the activity of gamma-tBAMT was very close to that of gamma-tBMTX in the DHFR inhibition assay, the AMT ester was more potent than the MTX ester against cells in culture and against L1210 leukemia in vivo. Only partial cross-resistance was shown against gamma-tBMTX and gamma-tBAMT in cultured cells that were resistant to MTX by virtue of a transport defect or a combination of defective transport and elevated DHFR activity.

Synthesis and antifolate properties of 10-alkyl-8,10-dideazaminopterins

The synthesis of 10-alkyl analogues of the potent antitumor agent 8,10-dideazaminopterin is described. Alkylation of appropriate alpha-alkyl homoterephthalate esters with 2,4-diamino-6-(bromomethyl)-8-deazapteridine afforded 10-alkyl-10-carboxy-4-amino-4-deoxy-8,10-dideazapteroic acid diesters. Ester cleavage and decarboxylation at C-10 were accomplished by heating with sodium cyanide in Me2SO at 170-180 degrees C to afford the 2,4-diamino-10-alkyl-8,10-dideazapteroic acids. The acids were coupled with diethyl glutamate, followed by saponification, to give the 10-alkyl-8,10-dideazaminopterins. The compounds were potent inhibitors of growth in folate-dependent bacteria, Streptococcus faecium and Lactobacillus casei. The 10-methyl and 10-ethyl analogues gave the highest percent increases in life span for mice infected with L1210 leukemia with ILS values of +203 and +235%, respectively.

Synthesis and antitumor activity of 10-alkyl-10-deazaminopterins. A convenient synthesis of 10-deazaminopterin

Requirements for large-scale synthesis of the potent antitumor drug 10-deazaminopterin have led to development of a facile synthesis of this compound and its 10-alkyl analogues. The lithium diisopropyl amide generated dianions of appropriate p-alkylbenzoic acids were alkylated with 3-methoxyallyl chloride. The resulting 4-(p-carboxyphenyl)-1-methoxy-1-butenes were brominated at pH 7-8 to afford the 2-bromo-4-(p-carboxyphenyl)butyraldehydes. Condensation with 2,4,5,6-tetraminopyrimidine and subsequent in situ oxidation of the resulting dihydropteridines yielded crystalline 10-alkyl-10-deaza-4-amino-4-deoxypteroic acids. The pteroic acids were coupled with diethyl glutamate via the mixed anhydride method, followed by saponification at room temperature, to give the target 10-deazaminopterins. The 10-alkyl compounds were approximately equipotent to 10-deazaminopterin as growth inhibitors of folate-dependent bacteria. Their abilities to inhibit Lactobacillus casei and L1210 derived dihydrofolate reductases were also similar. Transport properties in vitro were suggestive of an improved therapeutic index for the 10-alkyl analogues. Against L1210 in mice, the percent increase in life span at the LD10 dosage was +151% (methotrexate), +178% (10-deazaminopterin), +235% (10-methyl analogue), and +211% (10-ethyl analogue). 10,10-Dimethyl-10-deazaminopterin was less effective at an equimolar dosage, but the ILS at the maximum dose tested (72 mg/kg) was +135%. It was far less toxic than the other analogues possibly because of enhanced clearance.

10-Propargylaminopterin and alkyl homologues of methotrexate as inhibitors of folate metabolism

Reported antifolate activity against leukemia L1210 by N-[14-[[(2-amino-4-hydroxy-6-quinazolinyl)methyl]-propargylamino]benzoyl]]-L-glu tamic acid through potent inhibition of thymidylate synthase (EC 2.1.1.45) prompted us to include the propargyl group in a study of the effect on folate metabolism and membrane transport of replacing the 10-methyl group of methotrexate with other groups. Along with the propyl (8a) and octyl (8b) homologues of methotrexate, the propargyl compound 8c was prepared for evaluation. Syntheses of 8a,b were achieved by a standard multistep sequence involving preparation of the side-chain precursors via tosylated intermediates and then their alkylation with 6-(bromomethyl)-2,4-pteridinediamine hydrobromide. The side-chain precursor to 8c was prepared by direct alkylation of diethyl N-(4-aminobenzoyl)-L-glutamate with propargyl bromide and was separated from unchanged amine and dipropargyl coproduct by a combination of methods, including dry-column chromatography and recrystallization. Subsequent steps leading to 8c were like those used to prepare 8a,b. Biological evaluations of the three compounds consisted of studies of their effects on enzyme inhibition [(dihydrofolate reductase (EC 1.5.1.3) and thymidylate synthase)], L1210 cell growth inhibition, cellular membrane transport with various murine cell types (L210, S180, Ehrlich, and epithelial), in vivo (mice) activity vs. L1210 leukemia and S180 ascites, and plasma clearance in mice. The in vivo results vs. S180 ascites offered evidence that 8c might have a better therapeutic index against this tumor than methotrexate, but no other result from either of these compounds suggested significant superiority over methotrexate.

Folate analogues altered in the C9-N10 bridge region. 18. Synthesis and antitumor evaluation of 11-oxahomoaminopterin and related compounds

The chemical synthesis of 11-oxahomoaminopterin (1) has been carried out using procedures which were also found to be applicable to the synthesis of 11-oxahomofolic acid (2). Reaction of 1-bromo-4-[p-(caarbomethoxy)phenoxy]-2-butanone (10) with sodium azide gave 1-azido-4-[p-(carbomethoxy)phenoxy]-2-butanone (11). Protection of the carbonyl group of 11 as the ethylene ketal and subsequent base hydrolysis of the product gave 1-azido-4-(p-carboxyphenoxy)-2-butanone ketal (13). The glutamate conjugate 14 was prepared from 13 by the isobutyl chloroformate method and was hydrogenated to diethyl N-[(alpha-amino-2-oxo-4-butanoyl)-p-anisoyl]-L-glutamate ketal (15). Reaction of 15 with 6-chloro-2,4-diamino-5-nitropyrimidine (16) and 2-amino-6-chloro-4-hydroxy-5-nitropyrimidine (17) and deprotection of the corresponding products gave the intermediates 18 and 19, which were elaborated to 1 and 2 using a series of steps involving deprotection, dithionite reduction, cyclization, oxidation, and hydrolysis. Although 11-oxahomoaminopterin showed antifolate activity against two folate-requiring microorganisms and inhibited Lactobacillus casei DHFR, it was inactive against L-1210 leukemia in mice at a maximum dose of 48 mg/kg. Compound Lactobacillus casei DHFR, it was inactive against L-1210 leukemia in mice at a maximum dose of 48 mg/kg. Compound 1 was also tested for its ability to be transported via the methotrexate transport system using the L-1210 and Ehrlich tumor cell lines, and these results are compared with those of related analogues. The growth inhibitory activity of 1 in the L-1210 cell lines in culture was found to be 15 times weaker than that of methotrexate.

Convenient synthesis of 10-deazaaminopterin via a pteridine ylide

10-Deazaaminopterin, a potential antitumor agent now undergoing clinical trials, has been synthesized by a new approach involving the Wittig reaction. The ylide obtained by reaction of 6-(bromomethyl)-2,4-pteridinediamine with triphenylphosphine in Me2NAc, followed by treatment with NaOMe, underwent smooth reaction with diethyl N-(4-formylbenzoyl)-L-glutamate to give the vinyl precursor of the subject compound. Catalytic hydrogenation (Pt in glacial AcOH) of this product at ambient conditions led to uptake of 3 molar equiv of H2. Exposure to air during saponification of the ester groupings apparently gave the 7,8-dihydro compound according to UV spectral data, and further oxidation with H2O2 led to 10-deazaaminopterin.

Folate analogues altered in the C9-N10 bridge region. 10-Oxafolic acid and 10-oxaaminopterin

The unambiguous synthesis of two folate analogues, in which the 10-amino group of folic acid was replaced with oxygen, is described. The synthetic sequence employed commercially available methyl p-hydroxybenzoate and n-(2,3-epoxypropyl)phthalimide as starting materials. The use of cesium bicarbonate as a coreactant in the nucleophilic displacement reaction between bromo ketone 3 and the nucleophile 4 was found to be unique in character. The aminoacetonyl oxime 7 obtained by the hydrazinolysis of 6 was used as a common intermediate for the synthesis of both compounds. The generality of the use of the TFA-HCL mixture to deprotect the carbonyl group of both 10 and 12 reductions involving sodium hydrosulfite in aqueous dmf were further substantiated by conversions of 11 and 13 to 14 and 15 quickly and efficiently without employing catalytic hydrogenations. Subsequent cyclizations, oxidations, and hydrolysis of these reduction products to the pteroate analogues 17 and 19 were carried out efficiently as described for the synthesis of the sulfur analogues. Activation of the carboxyl group of 19 by way of the mixed anhydride 22 and subsequent coupling to glutamic acid was carried out using the solid-phase coupling procedure. However, compound 17 required trifluoroacetylation to 20 prior to the coupling reaction due to solubility problems. Both 10-oxafolic acid (1) and 10-oxaaminopterin (2) showed potent antifolate activity when tested against two folate-requiring organisms. Compound 2 was a very powerful inhibitor of DCM-resistant lactobacillus casei dihydrofolate reductase. The activity was comparable to that of methotrexate while the 4-hydroxy analogue did not show inhibition. 7,8-Dihydro-10-oxafolic acid failed to show any substrate activity to this enzyme and did not inhibit the enzymatic reaction when used with an equimolar concentration of the natural substrate.