TY - JOUR
T1 - Synthesis by radical cyclization and cytotoxicity of highly potent bioreductive alicyclic ring fused [1,2-a]benzimidazolequinones
AU - Lynch, Mary
AU - Hehir, Sarah
AU - Kavanagh, Paul
AU - Leech, Dónal
AU - O'Shaughnessy, John
AU - Carty, Michael P.
AU - Aldabbagh, Fawaz
PY - 2007
Y1 - 2007
N2 - The key step in the synthesis of new five, six and seven-membered alicyclic ring [1,2-a]-fused bioreductive benzimidazolequinones was radical cyclisation. Six and seven-membered tributyltin hydride-mediated homolytic aromatic substitutions of nucleophilic N-alkyl radicals onto the benzimidazole-2-position occurred in high yields (63-70%) when quaternising the pyridine-like 3-N of imidazole with camphorsulfonic acid and using large excesses of the azo-initiator, 1,1′-azobis-(cyclohexanecarbonitrile), to supplement the non-chain reaction. Elaboration of benzimidazoles to the benzimidazolequinones occurred in excellent yields. The IC50 values for the cytotoxicity of benzimidazolequinones towards the human skin fibroblast cell line GM00637 were in the nanomolar range, as determined by using the MTT assay. The benzimidazolequinones were much more cytotoxic than indolequinone analogues. 1,2,3,4-Tetrahydropyrido[1,2-a]benzimidazole-6,9-dione was the most potent compound prepared being more than 300 times more cytotoxic than the clinically used bioreductive drug, mitomycin C. The latter benzimidazolequinone was more potent under hypoxic conditions (associated with solid tumors), being 4.4 times more cytotoxic than under aerobic conditions, while mitomycin C was 1.8 times more selective towards hypoxia. The cyclopropane fused pyrido[1,2-a] benzimidazolequinone, 1a,2,3,9b-tetrahydro-1H-cyclopropa[3,4]pyrido[1,2-a] benzimidazole-5,8-dione was less cytotoxic and selective than the five-membered ring analogue, 1,1a,8,8a-tetrahydrocyclopropa-[3,4]pyrrolo[1,2-a]benzimidazole- 3,6-dione. Modifying the structure of the most potent pyrido[1,2-a] benzimidazolequinone by attaching methyl substituents onto the quinone moiety increased reductive potentials and decreased cytotoxicity and selectivity towards hypoxia.
AB - The key step in the synthesis of new five, six and seven-membered alicyclic ring [1,2-a]-fused bioreductive benzimidazolequinones was radical cyclisation. Six and seven-membered tributyltin hydride-mediated homolytic aromatic substitutions of nucleophilic N-alkyl radicals onto the benzimidazole-2-position occurred in high yields (63-70%) when quaternising the pyridine-like 3-N of imidazole with camphorsulfonic acid and using large excesses of the azo-initiator, 1,1′-azobis-(cyclohexanecarbonitrile), to supplement the non-chain reaction. Elaboration of benzimidazoles to the benzimidazolequinones occurred in excellent yields. The IC50 values for the cytotoxicity of benzimidazolequinones towards the human skin fibroblast cell line GM00637 were in the nanomolar range, as determined by using the MTT assay. The benzimidazolequinones were much more cytotoxic than indolequinone analogues. 1,2,3,4-Tetrahydropyrido[1,2-a]benzimidazole-6,9-dione was the most potent compound prepared being more than 300 times more cytotoxic than the clinically used bioreductive drug, mitomycin C. The latter benzimidazolequinone was more potent under hypoxic conditions (associated with solid tumors), being 4.4 times more cytotoxic than under aerobic conditions, while mitomycin C was 1.8 times more selective towards hypoxia. The cyclopropane fused pyrido[1,2-a] benzimidazolequinone, 1a,2,3,9b-tetrahydro-1H-cyclopropa[3,4]pyrido[1,2-a] benzimidazole-5,8-dione was less cytotoxic and selective than the five-membered ring analogue, 1,1a,8,8a-tetrahydrocyclopropa-[3,4]pyrrolo[1,2-a]benzimidazole- 3,6-dione. Modifying the structure of the most potent pyrido[1,2-a] benzimidazolequinone by attaching methyl substituents onto the quinone moiety increased reductive potentials and decreased cytotoxicity and selectivity towards hypoxia.
KW - Antitumor agents
KW - Benzimidazolequinones
KW - Radicals
KW - Synthetic methods
UR - http://www.scopus.com/inward/record.url?scp=34250632264&partnerID=8YFLogxK
U2 - 10.1002/chem.200601450
DO - 10.1002/chem.200601450
M3 - Article
C2 - 17200920
AN - SCOPUS:34250632264
SN - 0947-6539
VL - 13
SP - 3218
EP - 3226
JO - Chemistry - A European Journal
JF - Chemistry - A European Journal
IS - 11
ER -