Design and synthesis of potent non-polyglutamatable quinazoline antifolate thymidylate synthase inhibitors.

The synthesis is described of a series of analogues of the potent thymidylate synthase (TS) inhibitor, N-[4-[N-[(3,4-dihydro-2, 7-dimethyl-4-oxo-6-quinazolinyl)methyl]-N-prop-2-ynylamino]-2-f luorob enzoyl]-L-glutamic acid (4, ZM214888), in which the glutamic acid moiety is replaced by homologous amino acids and alpha-amino acids where the omega-carboxylate is replaced by acylsulfonamides and acidic heterocycles. In general these modifications when compared to 4 gave compounds with increased potency as inhibitors of isolated TS and as cytotoxic agents against murine tumor cell lines. The new compounds require transport by the reduced folate carrier for entry into cells but are not converted intracellularly into polyglutamated species. Agents with this profile are expected to show activity against tumors that are resistant to classical antifolates due to low expression of folylpolyglutamate synthetase. The analogue (S)-2-[4-[N-[(3,4-dihydro-2, 7-dimethyl-4-oxo-6-quinazolinyl)methyl]-N-prop-2-ynylamino]-2-f luorob enzamido]-4-(1H-1,2,3,4-tetrazol-5-yl)butyric acid (35, ZD9331) has been selected as a clinical development candidate and is currently undergoing phase I studies.

Cellular pharmacology and in vivo activity of a new anticancer agent, ZD9331: a water-soluble, nonpolyglutamatable, quinazoline-based inhibitor of thymidylate synthase.

ZD9331 is a drug that was developed from a potent class of water-soluble, C7-methyl-substituted, quinazoline-based inhibitors of thymidylate synthase (TS) that are transported into cells via a saturable, carrier-mediated system (reduced folate carrier, or RFC) but are not substrates for folylpolyglutamate synthetase. ZD9331 is the gamma-tetrazole analogue of 2-desamino-2, 7-dimethyl-N10-propargyl-2'fluoro-5,8-dideaza folate (ZM214888), with a TS Ki of approximately 0.4 nM. ZD9331 exhibits potent growth inhibitory and cytotoxic activity; e.g., IC50 for the inhibition of human W1L2 lymphoblastoid cell line was 7 nM. The addition of thymidine to the culture medium increased the IC50 in W1L2 cells >10, 000-fold, demonstrating the high specificity of the drug for TS. ZD9331 is transported into cells predominantly via the RFC. Accordingly, it competes with methotrexate (MTX) and folinic acid for cellular uptake and has reduced activity against two cell lines with low expression of the RFC (L1210:1565 and CEM/MTX). In addition, a cell line with acquired resistance to ZD9331 displays reduced uptake of both ZD9331 and MTX. A mouse cell line (L1210:RD1694), with acquired resistance to ZD1694 due to reduced folylpolyglutamate synthetase activity, was not significantly cross-resistant to ZD9331. The flux through TS, as measured by 3H release from 5-[3H]deoxyuridine, was rapidly inhibited when cells were incubated with ZD9331. However, because ZD9331 cannot form polyglutamates, TS activity recovered rapidly once cells were placed in drug-free medium. The minimum curative dose of ZD9331 in the i.m. L5178Y TK-/- tumor model was approximately 3 mg/kg when given by 24-h continuous infusion, and it was 25-50 mg/kg when given by a single i.p. or i.v. injection. ZD9331 had antitumor activity against the L5178Y TK+/- tumor when administered by 7-day continuous infusion; growth delays of more than 5 days (and some cures) were seen at doses of 25-50 mg/kg/day. At higher doses, significant weight loss (gastrointestinal toxicity) and myelosuppression (neutropenia and thrombocytopenia) were observed, suggesting that these may be dose-limiting toxicities in the Phase I clinical studies.

Quinazoline antifolates thymidylate synthase inhibitors: lipophilic analogues with modification to the C2-methyl substituent.

Modification of the potent thymidylate synthase (TS) inhibitor 1-[[N-[4-[N-[(3,4-dihydro-2-methyl-4-oxo-6-quinazolinyl)methyl]-N- prop-2-ynylamino]benzoyl]amino]methyl]-3-nitrobenzene (4a) has led to the synthesis of quinazolinone antifolates bearing functionalized alkyl substituents at C2. A general synthetic route was developed which involved coupling the appropriate 1-[[N-[4-(alkylamino)benzoyl)amino]methyl]-3-nitrobenzene 20-22 with a 6-(bromomethyl)-2-(acetoxymethyl)-3,4-dihydro-4-oxoquinazoline 9 or 10. Replacement of the 2-acetoxy group by a chlorine atom followed by the displacement of the halogen of 25a-c by various nucleophiles led to compounds 26-40. Good TS (IC50 < 1 microM) and growth inhibition (IC50 0.1-1 microM) were found with most of these new antifolates. TS inhibitors in this series do not apparently require the reduced folate carrier (RFC) for cell entry (they most likely penetrate the cell membrane by passive diffusion) and are not polyglutamated. N, O, S, Cl, and CN as well as large amino and mercapto substituents were tolerated by the enzyme. The simultaneous incorporation of 7-methyl and 2'-F substituents gave a series of highly potent agents inhibiting cell growth at concentrations < 1 microM (24, 27bc; 30-32b, 35b). The incorporation of suitable C2 substituents has overcome the decrease in aqueous solubility observed with lipophilic quinazoline antifolates. This is best illustrated by compound 31a, where up to a 54-fold increase in solubility has been achieved by the incorporation of an N-methylpiperazine nucleus into the C2-methyl group of 4a.

Quinazoline antifolate thymidylate synthase inhibitors: replacement of glutamic acid in the C2-methyl series.

The synthesis of a series of analogues of the potent thymidylate synthase (TS) inhibitor N-[4-[N-[(3,4-dihydro-2-methyl-4-oxo-6- quinazolinyl)methyl]-N-prop-2-ynylamino]benzoyl]-L-glutamic acid (ICI 198583, 1) is described in which the glutamic acid residue has been replaced by other alpha-amino acids. Most of these analogues were prepared by coupling of tert-butyl-4-(prop-2-ynylamino)benzoate (37) with 6-(bromomethyl)-3,4-dihydro-2-methyl-4-oxoquinazoline (34) followed by deprotection of the tert-butyl ester to the acid and azide-mediated coupling to the appropriate amino acid or amino acid ester. In cases where the amino acid ester was unreactive with the acid azide, a modification was used in which the quinazolinone moiety was protected as its 3-(pivaloyloxy)methyl derivative. This permitted the generation of the more reactive acid chloride of the p-aminobenzoate unit. In general these modifications result in compounds that have equivalent potency to 1 as inhibitors of isolated TS except where the amino acid lacks a lipophilic alpha-substituent. These compounds appear to require the reduced folate carrier (RFC) for transport into cells, but since they are not converted intracellularly into polyglutamated forms, they have a lower level of cytotoxicity compared to 1. The removal of the alpha-carboxylic acid has given a second set of analogues of 1 which contain simple alkyl amide, benzyl, substituted benzyl, and heterocyclic benzyl amide derivatives. These are considerably less potent than 1 as TS inhibitors but display 1-10 microM cytotoxicities due to the fact that they do not require RFC transport and can presumably readily enter cells by passive diffusion through the cell membrane. Molecular modeling and NMR studies indicated that the incorporation of, respectively, 7-methyl and 2'-fluoro substituents would favor the optimum conformation of these molecules for interaction with the TS enzyme. Accordingly, these substituents were incorporated into selected examples to give the series of analogues 47-55. These all show enhanced (approximately 10-fold) inhibition of TS compared to their unsubstituted counterparts. In the substituted benzylamides (51, 52) and heterocyclic benzyl amides (53-55) the ability to enter cells by passive diffusion results in highly potent (< 1 microM) cytotoxic agents.

Quinazoline antifolate thymidylate synthase inhibitors: heterocyclic benzoyl ring modifications.

The synthesis is described of a series of C2-methyl-N10-alkylquinazoline-based antifolates in which the p-aminobenzoate ring is replaced by the heterocycles thiophene, thiazole, thiadiazole, pyridine, and pyrimidine. These were generally elaborated by the reaction of (bromomethyl)quinazoline 18 or its N3-[(pivaloyloxy)methyl]-protected derivative 36 with suitable heterocyclic amines although each heterocyclic system required its own particular synthetic approach. The compounds were tested as inhibitors of partially purified L1210 thymidylate synthase (TS). They were also examined for their inhibition of the growth of L1210 cells in culture. The thiophene system 7 and its related thiazole 8 gave analogues that were considerably more potent than the parent benzene series 2 as inhibitors of L1210 cell growth although in general these heterocycles were somewhat poorer inhibitors of the isolated TS enzyme. The enhanced cytotoxicities of the thiophene and thiazole analogues result, at least in part, from their efficient transport into the cells via the reduced folate carrier mechanism and very good substrate activity for folylpolyglutamate synthetase. The replacement of the C2-methyl group by C2-(fluoromethyl) and C2-(hydroxymethyl) substituents in the thiophene and thiazole series gave derivatives that were only slightly less potent inhibitors of the TS enzyme but which were considerably less cytotoxic.

Synthesis and structure-activity relationships of a novel antifungal agent, ICI 195,739.

Antifungal azole derivatives are known to have potential for inhibition of host P-450 systems, and, in the attempts to increase the antifungal specificity of the inhibitor by identification of extra receptor binding within the enzyme complex, initial synthesis was guided by the structural requirements of the natural lanosterol substrate. With the aid of computer graphics, the 3'-styryl functionality was identified as a key structural element. For metabolically stable systems, in vitro-in vivo correlations exist, but optimizing oral activity resulted in the production of compounds with unacceptably long elimination half-lives. A disconnection of this relationship was achieved in pairs of structural isosteres with metabolic nonequivalence (CN:CONH2/OCH3:OCF3) and led to the identification of ICI 195,739, a novel 3'-tetrafluoropropoxystyryl-substituted bistriazole tertiary alcohol, as the compound of choice.