Abstract
Bolinaquinone is a natural product that is a structurally complex, cytotoxic sesquiterpene quinone. A scaffold simplification and focused library approach using a microwave-assisted Suzuki coupling gave 32 bolinaquinone analogues with good-to-excellent cytotoxicity profiles. Mono-arylbenzoquinones, Library A, were preferentially toxic towards BE2-C (neuroblastoma) cells with growth inhibition (GI50) values of 4–12 µM; only the 3,4-dimethoxyphenyl 23 and 3-biphenyl 28 variants were broad-spectrum active—HT29 (colon carcinoma), U87 and SJ-G2 (glioblastoma), MCF-7 (breast carcinoma), A2780 (ovarian carcinoma), H460 (lung carcinoma), A431 (skin carcinoma), Du145 (prostate carcinoma), BE2-C (neuroblastoma), MIA (pancreatic carcinoma) and SMA (spontaneous murine astrocytoma). Library B with a second aryl moiety exhibited broad-spectrum cytotoxicity with MCF-7 cells’ GI50 values of 5.6 ± 0.7 and 5.1 ± 0.5 µM for 2,5-dimethoxy-3-(naphthalene-1-yl)-6-(naphthalene-3-yl) 33 and 2,5-dimethoxy-3-(biaryl-2-yl)-6-(naphthalene-3-yl) 36, respectively. Similar potencies were also noted with 2,5-dimethoxy-3,6-diphenyl 30 against A2780 (GI50 = 5.9 ± 0.0 µM) and with 2,5-dimethoxy-3-(biaryl-3-yl)-6-(naphthalene-3-yl) 37 against HT29 (GI50 = 5.4 ± 0.4 µM), while the 3,4-dimethoxy mono-aryl analogue 23 exhibited good levels of activity against A2780 (GI50 = 3.8 ± 0.75 µM), the neuroblastoma cell line BE2-C (GI50 = 3 ± 0.35 µM) and SMA (GI50 = 3.9 ± 0.54 µM). Introduction of the amino-substituted Library C gave 2-(naphthalen-1-yl)-5-(naphthalen-3-yl)-3,6-bis(propylamino) 43, with excellent activity against HT29 (0.08 ± 0.0 µM), MCF-7 (0.17 ± 0.1 µM), A2780 (0.14 ± 0.1 µM), A431 (0.11 ± 0.0 µM), Du145 (0.16 ± 0.1 µM), BE2-C (0.08 ± 0.0 µM) and MIA (0.1 ± 0.0 µM).
Highlights
Cancer can be defined as a collection of diseases in which cells undergo aberrant division and at times invasive proliferation
With the desired bolinaquinone analogues 12–43 in hand, we examined their cytotoxicity against a panel of 11 tumour cell lines: HT29, U87 and SJ-G2, MCF-7, A2780, H460, A431, Du145, BE2-C, MIA, SMA and a normal breast cell line (MCF10A)
Our investigation of the bolinaquinone SAR commenced with an application of a scaffold simplification and focused library approach that saw the synthesis of mono-arylated dimethoxybenzoquinones (Library A)
Summary
Cancer can be defined as a collection of diseases in which cells undergo aberrant division and at times invasive proliferation. Despite the potential PAIN nature of quinones, it has been proposed that they be retained in phenotypic screening libraries, with a key argument being that the core motif is present in numerous clinically used drugs, e.g. the anthracyclines, mitomycin and mitoxantrone. Despite their mechanism of action remaining unknown, these agents are successfully used in the treatment of multiple cancers, pneumonia and multiple sclerosis. We explore a scaffold simplification approach in our efforts to develop the cytotoxicity structure–activity relationship of bolinaquinone analogues
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