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Carbenes derived from diazoimidazolecarboxylates 4 under thermal or photochemical conditions undergo O-H and N-H insertion reactions with alcohols and amines, respectively, in moderate yield, in competition with reduction in good H-donor solvents. Dichloromethane reacts to give the corresponding 4-chloroimidazole. Aromatic hydrocarbons are excellent traps for the imidazolylidene carbene and lead to a range of arylimidazole derivatives 7. Reaction with pyridine leads to the first example of a pyridinium ylide 8 formed from an imidazolylidene carbene, whereas irradiation in hexafluorobenzene gives the imidazoazocine 11, presumably by way of an initial norcaradiene intermediate.

New fluorinated 2-aryl-benzothiazoles, -benzoxazoles, and -chromen-4-ones have been synthesized and their activity against MCF-7 and MDA 468 breast cancer cell lines compared with the potent antitumor benzothiazole 5. Analogues such as 9a, b and 12a, d yielded submicromolar GI50 values in both cell lines; however, none of the new compounds approached 5 in terms of antitumor potency. For 5, binding to the aryl hydrocarbon receptor appeared to be necessary but not sufficient for growth inhibition.

The growth-inhibitory activities of an extensive series of quaternized quino[4,3,2- kl]acridinium salts against tumor cell lines in vitro have been measured and their biological properties interpreted in the light of differential binding to different DNA isoforms. Selectivity for quadruplex DNA binding and stabilization by compounds were explored through an array of methods: UV absorption and fluorescence emission spectroscopy, surface plasmon resonance, and competition dialysis. Quadruplex DNA interaction was further characterized through FRET and DNA polymerase arrest assays. Telomerase inhibition, inferred from the TRAP assay, is attributed to quadruplex stabilization, supported by the strong correlation (R(2) = 0.81) across the series between quadruplex DNA binding affinity and TRAP inhibition potency. Growth inhibition potency in the NCI60 human tumor cell line panel is more marked in compounds with greater DNA duplex binding affinity (R(2) = 0.82). Quantification of relative quadruplex and duplex binding affinity constants puts some of these ligands among the most selective quadruplex DNA interactive agents reported to date.

Interaction of 2-iodoaniline or 5-fluoro-2-iodoaniline with a range of arylsulfonyl chlorides affords sulfonamides that undergo Sonogashira couplings under thermal or microwave conditions with the alkyne 4-ethynyl-4-hydroxycyclohexa-2,5-dien-1-one followed by cyclization to 4-[1-(arylsulfonyl-1H-indol-2-yl)]-4-hydroxycyclo-hexa-2,5-dien-1-ones. This method allows for incorporation of a range of substituents into the arylsulfonyl moiety, and compounds showed selective in vitro inhibition of cancer cell lines of colon and renal origin, a feature of compounds bearing the quinol pharmacophore.

A new series of fluoro-, methoxyl-, and amino-substituted isoflavones have been synthesized as potential antitumor agents based on structural similarities to known flavones and isoflavones (quercetin and genistein respectively) and antitumor 2-phenylbenzothiazoles. Target compounds were synthesized using palladium-catalyzed coupling methodologies to construct the central aryl carbon-carbon single bond. The new isoflavone derivatives were tested for in vitro activity in human breast (MDA-MB-468 and MCF-7) and colon (HT29 and HCT-116) cancer cell lines. Low micromolar GI50 values were obtained in a number of cases, with the MDA-MB-468 cell line being the most sensitive overall. Notably, significant potentiation of growth inhibitory activity (GI50<1 microM for 12d, 12f, 12h, 12k, 12l, 12o but not the methylene-bridged derivative 12i) was observed when MDA-MB-468 cells were co-incubated with TBDD, a powerful inducer of cytochrome P450 (CYP)-1A1 activity, suggesting that isoflavone derivatives can act as substrates for CYP1A1 bioactivation.

A series of new 2-phenylbenzothiazoles has been synthesized on the basis of the discovery of the potent and selective in vitro antitumor properties of 2-(3,4-dimethoxyphenyl)-5-fluorobenzothiazole (8n; GW 610, NSC 721648). Synthesis of analogues substituted in the benzothiazole ring was achieved via the reaction of o-aminothiophenol disulfides with substituted benzaldehydes under reducing conditions. Compounds were evaluated in vitro in four human cancer cell lines, and compound 8n was found to possess exquisitely potent antiproliferative activity (GI(50) < 0.1 nM for MCF-7 and MDA 468). Potent and selective activity was also observed in the NCI 60 human cancer cell line panel. Structure-activity relationships established that the compound 8n stands on a pinnacle of potent activity, with most structural variations having a deactivating in vitro effect. Mechanistically, this new series of agents contrasts with the previously reported 2-(4-aminophenyl)benzothiazoles; compound 8n is not reliant on induction of CYP1A1 expression for antitumor activity.

Palladium(0)-mediated Suzuki-Miyaura and Heck transformations have been exploited to provide examples of 8-methylquino[4,3,2-kl]acridines and 8,13-dimethylquino[4,3,2-kl]acridinium iodides bearing bulky saturated (3-acetoxy)propyl or (E)-3-(morpholin-4-yl)-3-oxopropenyl substituents variously in the 3-, 6-, or 10-positions of the pentacyclic nucleus. The pharmacological/pharmaceutical properties of four compounds (4, RHPS4), (5, IH383), (6, RHPS16), and (17, RHPS19) were measured to assess their clinical potential as DNA G-quadruplex-stabilizing/telomerase inhibitory agents. The following properties were measured: stability in tissue culture media in the presence of A549 lung and MCF-7 breast tumor cells, metabolic stability when incubated with rat liver microsomes, and rate of uptake and subcellular location in A549 and MCF-7 cells. Compound 17 was unstable in tissue culture media, failed to achieve nuclear access, and was excluded from further consideration. Of the other agents, 4 exhibited the most favorable pharmaceutical profile: the agent has appropriate stability in the presence of tumor cells and rat liver microsomes and achieves rapid ingress into cell nuclei where the putative molecular target is located.

The parallel solution-phase synthesis of a series of 30 monohydroxylated (E)-stilbene analogues is described. In vitro screening revealed low micromolar activity (GI(50)) against the MDA MB 468 breast cancer cell line. Activity in MDA MB 468 cells correlated with the ability to induce apoptosis following drug treatment by the most potent agents in the series, e.g., 5dy and 5jy, an observation further reinforced by AnnexinV-FITC analysis and fluorescence microscopy.

A series of substituted 4-(1-arylsulfonylindol-2-yl)-4-hydroxycyclohexa-2,5-dien-1-ones (indolylquinols) has been synthesized on the basis of the discovery of lead compound 1a and screened for antitumor activity. Synthesis of this novel series was accomplished via the "one-pot" addition of lithiated (arylsulfonyl)indoles to 4,4-dimethoxycyclohexa-2,5-dienone followed by deprotection under acidic conditions. Similar methodology gave rise to the related naphtho-, 1H-indole-, and benzimidazole-substituted quinols. A number of compounds in this new series were found to possess in vitro human tumor cell line activity substantially more potent than the recently reported antitumor 4-substituted 4-hydroxycyclohexa-2,5-dien-1-ones(1) with similar patterns of selectivity against colon, renal, and breast cell lines. The most potent compound in the series in vitro, 4-(1-benzenesulfonyl-6-fluoro-1H-indol-2-yl)-4-hydroxycyclohexa-2,5-dienone (1h), exhibits a mean GI(50) value of 16 nM and a mean LC(50) value of 2.24 muM in the NCI 60-cell-line screen, with LC(50) activity in the HCT 116 human colon cancer cell line below 10 nM. The crystal structure of the unsubstituted indolylquinol 1a exhibits two independent molecules, both participating in intermolecular hydrogen bonds from quinol OH to carbonyl O, but one OH group also interacts intramolecularly with a sulfonyl O atom. This interaction, which strengthens upon ab initio optimization, may influence the chemical environment of the bioactive quinol moiety. In vivo, significant antitumor activity was recorded (day 28) in mice bearing subcutaneously implanted MDA-MB-435 xenografts, following intraperitoneal treatment of mice with compound 1a at 50 mg/kg.

Benzimidazole-N-oxide modifications of potent lipophilic dihydrofolate reductase (DHFR) inhibitors (e.g., methylbenzoprim 1 and dichlorobenzoprim 2) have been prepared by base-promoted cyclization of the nitrophenylbenzylamino groups to explore the possibility that abrogation of DHFR-inhibitory activity might reveal clues to an alternative anti-ras mechanism. Examples of the new series had only low growth inhibitory activities (GI(50) generally >50 microM) against colon HCT116 and lung HT29 cell lines but, unlike methylbenzoprim, this activity was unaffected by hypoxanthine/thymidine rescue.

The synthesis and antitumor evaluation of a series of new heteroaromatic- and aromatic-substituted hydroxycyclohexadienones ("quinols"), and their imine counterparts, are described. The quinols were synthesized via the addition of a lithiated aromatic moiety to a quinone ketal followed by deprotection. When the aromatic portion of the molecule is a fused heterobicyclic structure (e.g., benzothiazole derivative 7a), potent in vitro antitumor activity was observed in HCT 116 (GI50 = 40 nM) and HT 29 (GI50 = 380 nM) human colon as well in as MCF-7 and MDA 468 human breast cancer cell lines. When examined on the NCI Developmental Therapeutics Screening Program in vitro screen (60 human cancer cell lines), active compounds in this series consistently displayed a highly unusual pattern of selectivity; cytotoxicity (LC50) was concentrated in certain colon and renal cell lines only. Analogue 7a also showed in vivo antitumor activity against human RXF 944XL renal xenografts in nude NMRI mice and is the focus of further study.

Carboxylic acids derived from the amido groups of the antitumor agents mitozolomide and temozolomide have been conjugated to simple amino acids and peptides by carbodiimide coupling. Solid-state peptide synthesis has been applied to link the acids to DNA major groove-binding peptidic motifs known to adopt alpha-helical conformations. Attachment of the acids to pyrrole and imidazole polyamidic lexitropsins gave a series of potential DNA minor groove-binding ligands. In vitro biological evaluation of a limited number of these novel conjugates failed to demonstrate any enhanced growth-inhibitory activity compared to the unconjugated drugs; sites of alkylation at tracts of multiple guanines were also unaffected. Attachment of additional residues at C-8 of the imidazotetrazines did not perturb the chemistry of activation of the bicyclic nucleus, and biological sequelae can be rationalized by invoking the liberation of a common, diffusible, reactive chemical intermediate, the methanediazonium ion.

8-Carbamoyl-3-methylimidazo[5,1-d]-1,2,3,5-tetrazin-4(3H)-one (temozolomide, 1) is an anticancer prodrug. As part of investigations to probe its postulated mode of action using PET we have developed two rapid radiosynthetic routes for the preparation of temozolomide labeled with the short-lived positron emitter, carbon-11 (t(1/2) = 20.4 min). Reaction of 5-diazoimidazole-4-carboxamide (7) with the novel labeling agent [(11)C-methyl]methyl isocyanate (8) gave [3-N-(11)C-methyl]temozolomide (9) in 14-20% radiochemical yield from [(11)C-methyl]methyl isocyanate (8) (decay corrected). The position of radiolabeling in the 3-N-methyl group was confirmed by [(11/13)C]colabeling and subsequent carbon-13 NMR spectroscopy. Similarly, the reaction of 5-diazoimidazole-4-carboxamide (7) with [(11)C-carbonyl]methyl isocyanate (10) gave [4-(11)C-carbonyl]temozolomide (11) in 10-15% radiochemical yield from [(11)C-carbonyl]methyl isocyanate (10) (decay corrected). Apyrogenic samples of [3-N-(11)C-methyl]temozolomide (9) and [4-(11)C-carbonyl]temozolomide (11), with good chemical and radiochemical purities, have been prepared and used in human PET studies.

A series of water-soluble L-lysyl- and L-alanyl-amide prodrugs of the lipophilic antitumor 2-(4-aminophenyl)benzothiazoles has been synthesized to address formulation and bioavailability issues related to the desired parenteral administration of the chosen clinical candidate. The prodrugs exhibit the required pharmaceutical properties of good water solubility (in weak acid) and stability at ambient temperature and degradation to free base in vivo. The lysyl-amide of 2-(4-amino-3-methylphenyl)-5-fluorobenzothiazole (NSC 710305, 6d) has been selected for phase 1 clinical evaluation.

Two short routes to novel methylated pentacyclic quinoacridinium salts have been devised. New compounds display telomerase-inhibitory potency (<1 microM) in the TRAP assay. 3,11-Difluoro-6,8,13-trimethyl-8H-quino[4,3,2-kl]acridinium methosulfate (12d, RHPS4, NSC 714187) has a higher selectivity for triplex and quadruplex DNA structures than the 3,6,8,11,13-pentamethyl analogue (12c, RHPS3, NSC 714186) and a low overall growth-inhibitory activity in the NCI 60 cell panel (mean GI(50) 13.18 microM); in addition, the activity profile of 12d does not COMPARE with agents of the topoisomerase II class. Compound 12d is soluble in water, stable in the pH range of 5-9, efficiently transported into tumor cells, and is currently the lead structure for further elaboration in this new class of telomerase inhibitor.

The triazenyl-pyrimethamine derivative 3a (TAB), a potent and selective inhibitor of Pneumocystis carinii DHFR, was selected as the starting point for a lead optimization study. Molecular modeling studies, corroborated by a recent crystal structure determination of the ternary complex of P. carinii DHFR--NADPH bound to TAB, predicted that modifications to the acetoxy residue of the lead inhibitor could exploit binding opportunities in the vicinity of an active site pocket bounded by residues Ile33, Lys37, and Leu72. Substitutions in the benzyl moiety with electron-donating and electron-withdrawing groups were predicted to probe face-edge interactions with amino acid Phe69 unique to the P. carinii enzyme. New triazenes 10a--v and 12a--f were prepared by coupling the diazonium tetrafluoroborate salt 6b of aminopyrimethamine with substituted benzylamines or phenethylamines. The most potent of the new inhibitors against P. carinii DHFR was the naphthylmethyl-substituted triazene 10t (IC(50): 0.053 microM), but a more substantial increase in potency against the rat liver DHFR led to a reduction in selectivity (ratio rat liver DHFR IC(50)/P. carinii DHFR IC(50): 5.36) compared to the original lead structure 3a (ratio rat liver DHFR IC(50)/P. carinii DHFR IC(50): 114).

Synthetic routes to a series of mono- and difluorinated 2-(4-amino-3-substituted-phenyl)benzothiazoles have been devised. Whereas mixtures of regioisomeric 5- and 7-fluoro-benzothiazoles were formed from the established Jacobsen cyclization of precursor 3-fluoro-thiobenzanilides, two modifications to this general process have allowed the synthesis of pure samples of these target compounds. Fluorinated 2-(4-aminophenyl)benzothiazoles were potently cytotoxic (GI(50) < 1 nM) in vitro in sensitive human breast MCF-7 (ER+) and MDA 468 (ER-) cell lines but inactive (GI(50) > 10 microM) against PC 3 prostate, nonmalignant HBL 100 breast, and HCT 116 colon cells. The biphasic dose-response relationship characteristically shown by the benzothiazole series against sensitive cell lines was exhibited by the 4- and 6-fluoro-benzothiazoles (10b,d) but not by the 5- and 7-fluoro-benzothiazoles (10h,i). The most potent broad spectrum agent in the NCI cell panel was 2-(4-amino-3-methylphenyl)-5-fluorobenzothiazole (10h) which, unlike the 6-fluoro isomer (10d), produces no exportable metabolites in the presence of sensitive MCF-7 cells. Induction of cytochrome P450 CYP1A1, a crucial event in determining the antitumor specificity of this series of benzothiazoles, was not compromised. 10h is currently the focus of pharmaceutical and preclinical development.

Hydroxylated styrenes (tyrphostins) undergo oxidation by hypervalent iodine oxidants such as [(diacetoxy)iodo]benzene (DAIB) to give a range of products depending on the structure of the phenolic substrate, the solvent, the oxidant stoichiometry, and the purification strategy. Conditions have been developed to modify the phenolic component of the tyrphostin without affecting the appended substituted-vinyl moiety. Novel products include: unstable 2-acyloxy-2-methoxy-4-(substituted-vinyl)cyclohexadienones and their rearrangement products 2-acyloxy-4-hydroxy-3-methoxy-1-(substituted-vinyl)benzenes; phenyliodoniophenolates and their rearrangement products iodophenoxytyrphostins; and 3,3'-dialkoxy-2,2'-dihydroxy-5, 5'-di(substituted-vinyl)biphenyls. None of these oxidation products displayed enhanced activity in vitro in the NCI 60-cell line panel or in a panel of human breast cancer cell lines, compared to their tyrphostin precursors. The inhibitory activity of three representative tyrphostins (3e,n, 28) was not modulated by aerobic/anaerobic conditions in MCF-7 and MDA 468 cells and was independent of EGFR status in clones of ZR75B cells transfected with this receptor. Basal growth of MCF-7 cells was unaffected by co-administration of the growth factors EGF, TGF-alpha, IGF-I, and IGF-II, and the new agents did not inhibit EGFR and c-erbB2 autophosphorylation in cell lysates from MDA 468 or SkBr3 cells, respectively, suggesting that receptor tyrosine kinases are not targets for these compounds. Growth stimulation by the tyrphostin 3n in the ER(+) breast cell lines MCF-7, T47D, and ZR75-1 was abolished by 1 microM tamoxifen, suggesting that this compound has estrogen agonist activity.

New synthetic routes to a series of tetra- and pentacyclic acridines related in structure to marine natural products are reported. The novel water-soluble agent dihydroindolizino[7,6,5-kl]acridinium chloride 14 has inhibitory activity in a panel of non-small-cell lung and breast tumor cell lines exceeding that of m-AMSA. The salt inhibited the release of minicircle products of kDNA confirming that disorganization of topoisomerase II partly underlies the activity of the compound. COMPARE analysis of the NCI mean graph profile of compound 14 at the GI(50) level corroborates this conclusion with Pearson correlation coefficients (>0.6) to clinical agents of the topoisomerase II class: however, this correlation was not seen at the LC(50) level. The inhibitory action of 14 on Saccharomyces cerevisiae transfected with human topoisomerase II isoforms showed a 3-fold selectivity against the IIalpha isoform over the IIbeta isoform. Unlike m-AMSA, 14 is not susceptible to P-glycoprotein-mediated drug efflux and retains activity in lung cells with derived resistance to the topoisomerase II inhibitor etoposide.

The crystal structure of the ternary complex of NADPH, the potent antifolate [2, 4-diamino-5-¿3-[3-(2-acetyloxyethyl)-3-benzyltriazen-1-yl]-4 -chloroph enyl¿-6-ethylpyrimidine] (TAB, 1) and Pneumocystis carinii dihydrofolate reductase (pcDHFR), refined to 2.1 A resolution, reveals that TAB binds similar to the antifolates trimethoprim and methotrexate. These data also reveal multiple conformations for the binding geometry of TAB with two preferred orientations of the acetyloxy and benzyl groups that results from a 180 degrees rotation about the N2-N3 triazenyl bond. The methyl of the acetyloxy and benzyl ring of TAB probes large hydrophobic regions of the p-aminobenzoyl folate binding pocket of the active site, in particular the region near Phe69, which is unique to the pcDHFR sequence. These results confirm prior molecular modeling investigations of the binding of TAB to pcDHFR that identified four low-energy binding geometries, two involving rotations about the terminal N(2)-N(3) triazenyl linkage and two involving atropisomerism about the pivotal pyrimethamine-phenyl bond. The primary differences in the molecular dynamics (MD) models and those observed in this crystal complex result from small conformational changes in active-site residues on energy minimization. However, two MD models place the acetyloxy and benzyl ring groups in a region of the active site between the cofactor-binding region and the p-aminobenzoyl folate pocket; an orientation never observed in any DHFR crystal structure to date. These conformers interact with solvent near the enzyme surface and are probably not observed due to the loss of specific hydrogen bonds with the enzyme. The high species pcDHFR selectivity of TAB could be the result of ligand flexibility that enables multiple binding orientations at the enzyme active site. Further modification of the acetyloxy region of TAB could increase its potency and selectivity for pcDHFR.

2-(4-Aminophenyl)benzothiazoles 1 and their N-acetylated forms have been converted to C- and N-hydroxylated derivatives to investigate the role of metabolic oxidation in the mode of action of this series of compounds. 2-(4-Amino-3-methylphenyl)benzothiazole (1a, DF 203, NSC 674495) is a novel and potent antitumor agent with selective growth inhibitory properties against human cancer cell lines. Very low IC(50) values (<0.1 microM) were encountered in the most sensitive breast cancer cell lines, MCF-7 and T-47D, whereas renal cell line TK-10 was weakly inhibited by 1a. Cell lines from the same tissue origin, MDA-MB-435 (breast), CAKI-1 (renal), and A498 (renal), were insensitive to 1a. Accumulation and metabolism of 1a were observed in sensitive cell lines only, with the highest rate of metabolism occurring in the most sensitive MCF-7 and T-47D cells. Thus, differential uptake and metabolism of 1a by cancer cell lines may underlie its selective profile of anticancer activity. A major metabolite in these sensitive cell lines has been identified as 2-(4-amino-3-methylphenyl)-6-hydroxybenzothiazole (6c). Hydroxylation of 1a was not detected in the homogenate of previously untreated MCF-7, T-47D, and TK-10 cells but was readily observed in homogenates of sensitive cells that were pretreated with 1a. Accumulation and covalent binding of [(14)C]1a derived radioactivity was observed in the sensitive MCF-7 cell line but not in the insensitive MDA-MB-435 cell line. The mechanism of growth inhibition by 1a, which is unknown, may be dependent on the differential metabolism of the drug to an activated form by sensitive cell lines only and its covalent binding to an intracellular protein. However, the 6-hydroxy derivative 6c is not the 'active' metabolite since, like all other C- and N-hydroxylated benzothiazoles examined in this study, it is devoid of antitumor properties in vitro.

A pentacyclic acridine, 1H-2,3-dihydroindolizino[7,6,5-kl]acridinium chloride (1), related in structure to tetra- and pentacyclic marine natural products, has previously been shown to induce apoptosis in breast and non-small-cell lung tumor cell lines and shows significant differences in biological potency and antitumor profile from other intercalating agents based on the acridine framework. We report on the molecular recognition of the acridinium salt with DNA, quantified by optical spectroscopic methods, and have compared these results with the clinical agent amsacrine (m-AMSA). The results point to an intercalative association between 1 and G-C-rich sequences of DNA. We have synthesized a hexamer duplex d(ACGCGT)2, presenting two potential 5'-CpG recipient sites, and have investigated in detail by NMR and molecular modeling methods the orientational preferences of 1, particularly with regard to the pyrrolidine ring system. On the basis of the intermolecular nuclear Overhauser effect (NOE) data, four possible intercalation models were considered; no single model produced a significantly better fit than any of the others. The best fit to the experimental data was obtained by considering a dynamic equilibrium between the different intercalated orientations with the drug maximizing pi-overlap with the G-C base pairs at the intercalation site. We found little evidence for any degree of groove specificity imparted by the pyrrolidine ring. If these simulations have biological relevance they suggest that, at most, the agent induces only a transitory hot spot in the DNA which, evidently, is sufficient to be sensed by damage-recognition mechanisms of the cell.

2-(4-Aminophenyl)benzothiazoles display potent and selective antitumor activity against inter alia breast, ovarian, colon, and renal cell lines, but their mechanism of action, though yet to be defined, may be novel. Metabolism is suspected to play a central role in the mode of action of these benzothiazoles since drug uptake and biotransformation were observed in sensitive cell lines (e.g., breast MCF-7 and MDA 468 cells) in vitro, whereas insensitive cell lines (e.g., prostate PC 3 cells) showed negligible uptake and biotransformation. N-Acyl derivatives of the arylamines have been synthesized, and in vitro studies confirm N-acetylation and oxidation as the main metabolic transformations of 2-(4-aminophenyl)benzothiazoles, with the predominant process being dictated by the nature of the 3'-substituent. The prototype amine 3 underwent mainly N-acetylation in vitro, while 3'-substituted analogues 4 and 5 were primarily oxidized. N-Acetylation of 4 to 11 exerts a drastic dyschemotherapeutic effect in vitro, but acetylation of the halogeno congeners 5-7 gave acetylamines 12-14 which substantially retain selective antitumor activity. In vivo pharmacokinetic studies in rats confirmed rapid and exclusive N-acetylation of the 3'-methyl analogue 4, but less acetylation with the 3'-chloro analogue 5. Distinct expression patterns of N-acetyltransferase NAT1 and NAT2 have been demonstrated in our panel of cell lines.

Three new pathways to the antitumor drug temozolomide (4) have been explored via intermediates 3, 6, and 7. The key intermediate 5-amino-1-(N-methylcarbamoyl)imidazole-4-carboxamide (6) has been successfully converted to 4 in 45% yield by employing sodium nitrite in aqueous tartaric acid at 0-5 degrees C. Compound 6 is prepared from nitrophenyl carbamate 14a and methylamine or directly from 5-aminoimidazole-4-carboxamide (13) and either methyl isocyanate or N-methylcarbamoyl chloride. Temozolomide (4) is also prepared from 8-cyano-3-methylimidazo[5,1-d]-1,2,3,5-tetrazin-4(3H)-one (7) by hydrolysis to the hydrochloride salt of 4 in 10 M hydrochloric acid. Compound 7is prepared from either 5-diazoimidazole-4-carbonitrile (28) and methyl isocyanate or by diazotization of 5-amino-1-(N-methylcarbamoyl)imidazole-4-carbonitrile (25). Attempts to cyclize 5-(3-methyltriazen-1-yl)imidazole-4-carboxamide (3) with phosgene or phosgene equivalents were unsuccessful: only 2-azahypoxanthine (11) was isolated.

Triazenyl-substituted pyrimethamine derivatives 10a-s have been prepared by coupling diazotized 2,4-diamino-5-(3-amino-4-chlorophenyl)-6-ethyl pyrimidine (1c) with a series of secondary amines in aqueous sodium carbonate solution. The triazenes which are stable and poorly soluble as free bases form more soluble, but unstable, salts with alkanesulfonic acids. The lead dimethyltriazene 2,4-diamino-5[4-chloro-3-(3,3-dimethyltriazen-1-yl)phenyl]-6-et hylpyrimidine (4a) forms a crystalline ethanesulfonic acid salt (solvated with 2-propanol), which is protonated at the pyrimidine N-1 position, as determined by X-ray crystallography. The ability of these new triazenes to inhibit Pneumocystis carinii dihydrofolate reductase in vitro has been compared to that of triazene 4a. The most potent and selective compound, 2,4-diamino-5-[3-[3-[2-(acetyloxy)ethyl]-3-benzyltriazen-1-y l]-4- chlorophenyl]-6-ethylpyrimidine (14a), has an IC50 value of 0.17 microM against the microbial enzyme and potentially useful selectivity (rat liver IC50/P. carinii IC50 = 114).

A new series of 2-(4-aminophenyl)benzothiazoles substituted in the phenyl ring and benzothiazole moiety has been synthesized by simple, high-yielding routes. The parent molecule 5a shows potent inhibitory activity in vitro in the nanomolar range against a panel of human breast cancer cell lines, but is inactive (IC50 > 30 microM) against other cell types: activity against the sensitive breast lines MCF-7 and MDA 468 is characterized by a biphasic dose-response relationship. Structure-activity relationships derived using these cell types has revealed that activity follows the heterocyclic sequence benzothiazole > benzoxazole >> benzimidazole and that 2-(4-aminophenyl)benzothiazoles bearing a 3'-methyl- 9a, 3'-bromo- 9c, 3'-iodo- 9f, and 3'-chloro-substituent 9i are especially potent and their activity extends to ovarian, lung, and renal cell lines. Four compounds have been evaluated in vivo against human mammary carcinoma models in nude mice. Compound 9a showed the most potent growth inhibition against the ER+ (MCF-7 and BO) and ER- (MT-1 and MT-3) tumors. Our efforts to identify a pharmacological mechanism of action for these intriguing compounds have not, as yet, been successful.

A series of new imidazo[5,1-d]-1,2,3,5-tetrazinones with additional hydrogen-bonding or ionic substituents at the 8-carboxamide position of the antitumor drugs temozolomide (1) and mitozolomide (2) has been prepared. None of these compounds were significantly more cytotoxic in vitro against the mouse TLX5 lymphoma than the lead structures. Molecular modeling techniques have been used to design benzo- and pyrazolo[4,3-d]-1,2,3-triazinones bearing carboxamide groups in appropriate positions which are isosteric with temozolomide and mitozolamide but which cannot ring open to alkylating species. As predicted, these compounds have no inhibitory properties against human GM892A or Raji cell lines in vitro. Temozolomide and the spermidine-temozolomide conjugate 28 preferentially methylate guanines within guanine-rich sequences in DNA, but no experimental evidence has been found to support the hypothesis that such regions are involved in catalyzing the ring opening of the imidazotetrazinone prodrugs to their active forms.

The hypothesis that the antitumor prodrug temozolomide is ring-opened to MTIC which then further breaks down to a reactive diazonium ion at guanine-rich sequences in DNA has been probed by NMR spectroscopy and computational techniques. Temozolomide is stable at acid pH but decomposes to MTIC at pH > 7; in contrast, MTIC is stable at alkaline pH values but rapidly fragments in a methylating mode at pH < 7. The proximate methylating agent is the reactive methyldiazonium species. Runs of guanine residues represent an accessible nucleophilic microenvironment in DNA site-specific conversion of the prodrug temozolomide to MTIC possibly via an activated water molecule in the major groove. Molecular modeling of the structure of temozolomide indicates that the prodrug can make a favorable noncovalent encounter with DNA. The known structure-activity relationships as well as the biological and clinical properties of temozolomide can be interpreted in terms of this model.

A series of polyhydroxylated 2-phenylbenzothiazoles 3 has been prepared by demethylation of the precursor methoxylated 2-phenylbenzothiazoles 9. The key step in the construction of the benzothiazole nucleus involves a Jacobson cyclization of methoxylated thiobenzanilides 8. The target compounds inhibit WiDr human colon tumor cells and MCF-7 human mammary tumor cells in vitro with IC50 values in the low micromolar range, but the activity against MCF-7 cells is not related to estrogen receptor-binding affinity. None of the compounds showed selective cytotoxicity against Abelson virus-transformed ANN-1 cells encoded with the pp120gag-abl tyrosine kinase compared with the parental 3T3 line. Compounds were only marginally inhibitory to the EGF receptor-associated protein tyrosine kinase from a membrane preparation of A431 cells. The most active compound was 4,6-dihydroxy-2-(4-hydroxyphenyl)benzothiazole (3b) which has the same overall hydroxyl substitution pattern as genistein (1a). The compounds were weakly cytotoxic for an EGF receptor, overexpressing cell line HN5, but when tested for differential toxicity against the EGF receptor tyrosine kinase or the PDGF receptor tyrosine kinase in a standard mitogenesis assay utilizing human fibroblasts, no discrimination was observed. In this assay, the compounds inhibited DNA synthesis when added to cells during S phase. This suggests that inhibition could not be interpreted in terms of tyrosine kinase inactivation but more likely as a relatively broad specificity for the ATP-binding domain of other kinases such as thymidine kinase.

The antitumor imidazotetrazinone, temozolomide (5), C6H6N6O2, forms crystals with unit cell dimensions a = 17.332 (3), b = 7.351 (2), c = 13.247 (1), beta = 109.56 (1) degree and space group P21/c. A doubly hydrogen-bonded dimer constitutes the asymmetric unit. One carboxamide group forms an additional intermolecular NH...O hydrogen bond; in both molecules the carboxamide group is coplanar with the heterocycle and its NH2 group interacts with the imidazole nitrogen atom N(7). Molecular orbital calculations show the carbonyl carbon C(4) to be the most electron deficient atom, with relatively weak N(3)-C(4) and C(4)-N(5) bonds confirming that temozolomide should ring-open at this position in solution. The energy barrier to carboxamide group rotation of approximately 20 kJ mol-1 should permit interconversion between rotamers. In temozolomide and the related drug mitozolomide (4), N(7) is more negatively charged than N(1), which favors the formation of hydrogen bonds to the former atom in spite of their poor geometry. The relevance of these structural features to the action of temozolomide as a major-groove-directed prodrug of the alkylating agent MTIC (3) is discussed.

Methylbenzoprim (MBP) is a potent inhibitor of dihydrofolate reductase, which is more selective for mammalian than bacterial enzymes. Crystal-structure studies on the free base of MBP, with two independent molecules, and the ethanesulfonate salt, have demonstrated three significantly different conformations for MBP. With the MOPAC optimized MBP cation as starting point, the COSMIC energy was monitored as torsion angles were changed in 5 degrees increments. The barrier to rotation about C(5)-C(11) can create two slowly interconverting rotamers, in agreement with NMR studies. Two conformations of the cation that fit the human DHFR structure from the Brookhaven Protein Data Bank have been found. They differ chiefly by a half-turn about C(5)-C(11), positioning the nitro group on opposite sides but allowing the central and benzylic rings to find hydrophobic surroundings. The central ring is close enough to the predicted position of the cofactor NADPH to make competition likely. Kinetic studies with rat liver DHFR show that MBP is an inhibitor that competes with NADPH as well as dihydrofolate.

1H and 19F NMR signals from bound ligands have been assigned in one- and two-dimensional NMR spectra of complexes of Lactobacillus casei dihydrofolate reductase with various pyrimethamine analogues (including pyrimethamine [1, 2,4-diamino-5-(4'-chlorophenyl)-6-ethylpyrimidine], fluoropyrimethamine [2, 2,4-diamino-5-(4'-fluorophenyl)-6-ethylpyrimidine], fluoronitropyrimethamine [3, 2,4-diamino-5-(4'-fluoro-3'-nitrophenyl) -6-ethylpyrimidine], and methylbenzoprim [4, 2,4-diamino-5-[4'- (methylbenzylamino)-3'-nitrophenyl]-6-ethylpyrimidine]). The signals were identified mainly by correlating signals from bound and free ligands by using 2D exchange experiments. Analogues (such as 1 and 2) with symmetrically substituted phenyl rings give rise to 1H signals from four nonequivalent aromatic protons, clearly indicating the presence of hindered rotation about the pyrimidine-phenyl bond. Analogues containing asymmetrically substituted aromatic rings (such as 3 and 4) exist as mixtures of two rotational isomers (an enantiomeric pair) because of this hindered rotation and the NMR spectra revealed that both isomers (forms A and B) bind to the enzyme with comparable, though unequal, binding energies. In this case two complete sets of bound proton signals were observed. The phenyl ring protons in each of the two forms experience essentially the same protein environment (same shielding) as that experienced by the corresponding protons in bound pyrimethamine: this confirms that forms A and B correspond to two rotational isomers resulting from approximately 180 degrees rotation about the pyrimidine-phenyl bond, with the 2,4-diaminopyrimidine ring being bound similarly in both forms. The relative orientations of the two forms have been determined from NOE through-space connections between protons on the ligand and protein.(ABSTRACT TRUNCATED AT 250 WORDS)

The preparation of 3-(2-chlorethyl)-4-oxo-3H-imidazo[5,1-d]-1,2,3,5- tetrazine-8-carboxylic acid, a key derivative of mitozolomide in our exploration of the structure-activity relationships of this class of antitumor agents, is described. The facile conversion to the 8-carbonyl chloride gave a derivative that reacted preferentially with nucleophiles at the 8-position rather than at the reactive 4-oxo group, allowing the preparation of a wide range of ester, thioester, amide (including an amide derived from an amino acid), hydroxamic acid, hydrazide and sulfoximide, azide and diazoacetyl derivatives. The in vivo activity is presented of a range of these compounds against TLX5 lymphoma and L1210 leukemia cell lines.

Interaction of 5-diazoimidazole-4-carboxamide and alkyl and aryl isocyanates in the dark affords 8-carbamoyl-3-substituted-imidazo[5,1-d]-1,2,3,5-tetrazin-4(3H)-on es. In cold methanol or ethanol, the 3-(2-chloroethyl) derivative 7a decomposes to afford 2-azahypoxanthine (14) and methyl and ethyl N-(2-chloroethyl)carbamates, respectively. Compound 7a has curative activity against L-1210 and P388 leukemia and may act as a prodrug modification of the acyclic triazene 5-[3-(2-chloroethyl)triazen-1-yl]imidazole-4-carboxamide (MCTIC), since it ring opens to form the triazene in aqueous sodium carbonate.

1-Aryl-3-(hydroxymethyl)-3-alkyltriazenes [ArN = NN(CH3)CH2OH] have been synthesized by diazonium coupling to the carbinolamine (RNHCH2OH), generated in situ from the alkylamine and formaldehyde mixtures. The (hydroxymethyl)triazene structure has been confirmed by IR, NMR, and mass spectral analysis and also by the preparation of a crystalline benzoate derivative. The mass spectra of the (hydroxymethyl)triazenes suggest that they fragment by loss of formaldehyde to give the methyltriazene, which is also the product of hydrolysis in solution. The degradation of the (hydroxymethyl)triazenes in solution has been followed by UV spectroscopy and by HPLC analysis, and the half-lives were determined under a variety of conditions. The half-lives of the corresponding methyl- and (hydroxymethyl)triazenes are very similar. Both methyl- and (hydroxymethyl)triazenes decompose on silica plates during TLC analysis to give products consistent with known diazo-migration reactions. The (hydroxymethyl)triazenes have pronounced antitumor activity against the TLX5 tumor in vivo; in vivo-in vitro bioassay experiments suggest that the (hydroxymethyl)triazenes exert their in vivo antitumor activity via the degradation product, the alkyltriazene.

The systematic variation of the potent antitumor agent mitozolomide (1) is extended to cover alteration of substituents at positions 6 and 8 and to change the imidazo[5,1-d]-1,2,3,5-tetrazinone (1) skeleton to the isomeric pyrazolo-[5,1-d]-1,2,3,5-tetrazinone (17) skeleton. The series of eight 6-alkyl and 6-aralkyl derivatives of 1 showed optimal antitumor activity when the group was small or linear, but activity diminished as size and branching of this substituent increased. This may reflect altered transport characteristics, or failure of the enlarged derivatives to fit a binding site, or possibly a reduced tendency for the derivatives having bulky groups at position 6 to hydrolytically generate the putatively active triazenes (21). Testing of 14 derivatives of 1 differently substituted at position 8 revealed a complex structure-activity relationship, with good antitumor activity obtained for carbamoyl and sulfamoyl groups bearing small substituents. The 8-methylsulfonyl compound had noteworthy activity, but the 8-cyano, 8-nitro, and 8-phenyl derivatives were devoid of useful antitumor activity in these tests. From the limited number of pyrazolotetrazinones (17) reported here, it is suggested that the same conclusions as regards activity also hold true for this ring system.

A series of 2,4-diamino-5-aryl-6-ethylpyrimidines embracing basic substituents in the 5-aryl ring was synthesized and evaluated for inhibitory activity against rat liver dihydrofolate reductase (DHFR). Maximal enzyme inhibition was observed for compounds bearing a benzylamino (19) or N-alkylbenzylamino substituent (29 and 30) in the 4-position of the phenyl ring and a nitro group in the 3-position, the corresponding 3-amino, 3-azido, or unsubstituted analogues proving only weakly active or inactive as DHFR inhibitors. Selected compounds were also screened in vivo against a methotrexate-resistant tumor, the M5076 murine reticulosarcoma, and antitumor activity in general paralleled activity against DHFR, the (3,4-dichlorobenzyl)amino analogue 26 proving the least toxic compound to exhibit significant antitumor activity. The X-ray crystal structure of the ethanesulfonic acid salt of the N-methylbenzylamino compound 29 has been determined to facilitate future molecular modeling studies in this new series of DHFR inhibitors.

A series of derivatives of N-methylformamide (NMF), an experimental antitumor agent, has been prepared, having the general formula R3C(X)NR1R2 where R1 = H, CH3, CD3, CH2CF3, CH2CH2Cl, cyclopropyl, C2H5, CH2OH, CH2OR, CH2N(CH3)2; R2 = H, CH3; R3 = H, CF3, CCl3, CH3, Ph, NHCH3, N(CH3)2; and X = O, S, NH. A further short series of "push-pull" olefins of the general formula R1R2C = CHNR3R4 has been synthesized where R1 = H, CH3 and R2 = H, NO2, CN, CHO, CH3 and R3 = H and R4 = H, CH3, morpholino. These compounds have been tested for activity against the M5076 ovarian sarcoma and the TLX5 lymphoma in mice. NMF was by far the most potent agent of both series with activity against both tumors. Some other compounds showed weak activity, but there is a rigorous structural requirement for activity and most analogues were inactive. Certain members of the series exist as equilibrium mixtures of rotamers about the amide or pro-amide bonds as shown by NMR.