Synthetic strategies to a telomere-targeted pentacyclic heteroaromatic salt

Abstract

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 3. Application of a 6-(2-azidophenyl)phenanthridine precursor 11 gave an entry to the indazolo[2,3-f]phenanthridine ring system 12 not the required quino[4,3,2-kl]acridine. A six step synthesis starting from 2,6-dibromo-4-methylbenzonitrile 13via a 1-arylacridin-9(10H)-one intermediate, 19 or 21, gave the required 3 in low overall yield (<10%). The most efficient route entailed the one-pot (five step) conversion of 1,2-dimethyl-6-fluoroquinolinium methosulfate 23 to 3 in 33% yield employing triethylamine as base and nitrobenzene as solvent.