A series of N-14 sidechain substituted analogues of styelsamine (pyrido[4,3,2-mn]acridine) and cystodytin (pyrido[4,3,2-mn]acridin-4-one) alkaloids have been prepared and evaluated for their DNA binding affinity and antiproliferative activity towards a panel of human tumor cell lines. Overall it was found that styelsamine analogues were stronger DNA binders, with the natural products styelsamines B and D having particularly high affinity (Kapp 5.33 × 106 and 3.64 × 106 M−1, respectively). In comparison, the cystodytin iminoquinone alkaloids showed lower affinity for DNA, but were typically just as active as styelsamine analogues at inhibiting proliferation of tumor cells in vitro. Sub-panel selectivity towards non-small cell lung, melanoma and renal cancer cell lines were observed for a number of the analogues. Correlation was observed between whole cell activity and clogP, with the most potent antiproliferative activity being observed for 3-phenylpropanamide analogues 37 and 41 (NCI panel average GI50 0.4 μM and 0.32 μM, respectively) with clogP ~4.0–4.5.
Synthesis of the antimicrobial marine natural product halocyamine A has been achieved utilizing a combination of Sonogashira coupling, ruthenium complex/ytterbium triflate catalyzed hydroamidation and solid-phase peptide synthesis (SPPS) chemistry. The synthetic natural product exhibited only modest levels of antibacterial activities but significant antioxidant activity.
In an effort to explore the antibacterial potential of the marine natural product halocyamine A, a series of analogues including desbromo and alanine-substituted variants were synthesised and evaluated for biological activity against a panel of Gram-positive and-negative bacteria. The analogues were synthesised by a combination of solid-phase peptide synthesis and ruthenium complex/ytterbium triflate catalysed hydroamidation chemistry. Single alanine substitutions ([Ala 1 ]-halocyamine A and [Ala 2 ]-halocyamine A) gave only modest increases in activity towards Gram-positive bacteria, while di-alaninyl variants exhibited more potent activity with MIC values of 12.5-50 M towards the Gram-positive bacteria S. aureus and E. faecalis. A lipophilic trityl-protected intermediate of [Ala 2 ]halocyamine was the most active against the Gram negative bacterium Escherichia coli.
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