Ian Hutchinson

The regiospecific synthesis of 5- and 7-monosubstituted and 5,6-disubstituted 2-arylbenzothiazoles†

Abstract The regiospecific synthesis of a range of antitumour 2-arylbenzothiazoles substituted in the benzothiazole ring is described. In this procedure a bromine atom situated ortho to the anilido nitrogen is used to direct a regiospecific cyclisation where, in the absence of bromine, a mixture of regioisomers is produced. The chemistry described is applicable to the synthesis of 2-arylbenzothiazoles bearing both electron-withdrawing (-NO 2 ) and electron-donating (-NH 2 ) substituents on the aryl ring.

Antitumor Polycyclic Acridines. 20. Search for DNA Quadruplex Binding Selectivity in a Series of 8,13-Dimethylquino[4,3,2-kl]acridinium Salts: Telomere-Targeted Agents

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.

Synthetic strategies to a telomere-targeted pentacyclic heteroaromatic salt

Three routes have been explored to synthesise the telomere-targeted agent 3,11-difluoro-6,8,13-trimethyl-8H-quino[4,3,2-kl]acridinium methosulfate . Application of a 6-(2-azidophenyl)phenanthridine precursor gave an entry to the indazolo[2,3-f]phenanthridine ring system not the required quino[4,3,2-kl]acridine. A six step synthesis starting from 2,6-dibromo-4-methylbenzonitrile via a 1-arylacridin-9(10H)-one intermediate, or , gave the required in low overall yield (<10%). The most efficient route entailed the one-pot (five step) conversion of 1,2-dimethyl-6-fluoroquinolinium methosulfate to in 33% yield employing triethylamine as base and nitrobenzene as solvent.

Synthesis and properties of bioactive 2- and 3-amino-8-methyl-8H-quino[4,3,2-kl]acridine and 8,13-dimethyl-8H-quino[4,3,2-kl]acridinium salts

Cyclisation of 9-(benzotriazol-1-yl)acridine to the pentacycle 8H-quino[4,3,2-kl]acridine in a range of low-boiling solvents is mechanistically distinct from previously published photochemical (carbene) and thermolytic (radical) cyclisations. Fragmentation of the triazole ring of to a diazonium intermediate, and its subsequent heterolysis (-N(2)) and cyclisation is facilitated by solvation of intermediate zwitterionic species. Derivatives of 2- and 3-aminoquinoacridines methylated in the 8-position can be converted to 8,13-dimethylquino[4,3,2-kl]acridinium iodide salts with methyl iodide and were required for biological examination as potential telomerase inhibitors. The chloro group in 3-chloro-8-methyl-8H-quino[4,3,2-kl]acridine can be replaced efficiently by benzylamino, 4-morpholinyl and cyano substituents in palladium(0) mediated reactions.

Structural studies on bioactive compounds. 1 Heck reactions on 4-methyl-enepyrazolo[5,1-c][1,2,4]triazines

1-(3-Methyl-4-methylenepyrazolo[5,1-c][1,2,4]triazin-6(4H-yl)ethanone 9a and its 7-methyl- 9b and 7-phenyl-derivative 9c undergo Heck coupling to afford (Z)-1-{4-benzylidene-3-methylpyrazolo[5,1-c][1,2,4]triazin-6(4H)-yl}ethanones 10a–c and substituted benzylidene analogues 10d–m as the major geometrical isomers in low yields. The most potent agent in a human tumour screen in vitro was 10b (mean GI50 value 4.9 μM in a panel of 60 human cancer cell lines), with evidence of selective action against colon KM12 (GI50 0.02 μM) and breast MCF-7 tumour cell lines (GI501.35 μM).

Abstract C171: On‐ and off‐target effects of telomere uncapping G‐quadruplex ligands based on pentacyclic acridinium salts

Antitumor properties of the potent G‐quadruplex ligand 3,11‐difluoro‐6,8, 13‐trimethyl‐8H‐quino[4,3,2‐kl]acridinium methosulfate (RHPS4) are driven by telomere uncapping events. RHPS4 has good selectivity for quadruplex DNA over duplex DNA as measured by surface plasmon resonance (Kquad 1.1 × 107 M−1); Kdup 3.4 × 105 M−1). In preclinical models of solid tumor xenografts RHPS4 potentiates the activity of camptothecins but good response is dependent on the timing of the drug sequence employed. These experiments teach how an agent of this novel class might be used clinically in combination with chemotherapeutic agents. Although RHPS4 has several ‘drug‐like’ qualities (synthetic accessibility, water solubility, cellular uptake), a preliminary toxicological study revealed that the compound is a potent hERG inhibitor (IC50 0.2 M) and has additional receptor interactions, notably with muscarinic M1, M2 and M3 receptors. In an anaesthetized guinea pig cardiac model RHPS4 increased QTcB interval at doses of 5 and 10 mg/kg. Modifications to the peripheral substituents around the pentacyclic core have identified agents with differing on‐ and off‐target effects. Removal of the N(13)‐methyl group of RHPS4 to generate an uncharged molecule drastically reduced affinity for the target quadruplex DNA coupled with reduced pharmacological liabilities; increasing the size of the onium group at N(13) from Me to Et reduced affinity for quadruplex DNA (Kquad 0.6 × 106 M−1) and increased hERG inhibition (IC50 0.04 M). After a significant redesign program two isomeric compounds have been identified, 2‐ and 3‐acetylamino‐8,13‐dimethyl‐8H‐quino[4,3,2‐kl]acridinium iodides with ‘win‐win’ profiles ‐ better selectivity for quadruplex DNA and markedly reduced hERG liability (for the 2‐acetylamino compound Kquad 2.4 × 107 M−1; Kdup 3.8 × 105 M−1; hERG IC50 3.7 M): for the 3‐acetylamino isomer Kquad 2.5 × 107 M−1; Kdup 4.4 × 105 M−1; hERG IC50 18 M). Molecular modeling studies on the favored 3‐acetylamino derivative indicate that the pentacyclic core acts as a surrogate K+ stabilizing the G‐quadruplex structure with the acetylamino side‐chain projecting into a quadruplex groove. Citation Information: Mol Cancer Ther 2009;8(12 Suppl):C171.