No abstract

trans-Platinum(ii) oxadiazoline complexes with 7-nitro-1,3,5-triazaadamantane (NO-TAA) or hexamethylenetetramine (hmta) ligands have been synthesised from trans-[PtCl(PhCN)] via cycloaddition of nitrones to one of the coordinated nitriles, followed by exchange of the other nitrile by NO-TAA or hmta. Stoichiometric control allows for the selective synthesis of mono- and dinuclear complexes where 7-NOTAA and hmta act as mono- and bidentate ligands, respectively. Precursors and the target complexes trans-[PtCl(hmta)(oxadiazoline)], trans-[PtCl(NO-TAA)(oxadiazoline)] and trans-[{PtCl(oxadiazoline)}(hmta)] were characterised by elemental analysis, IR and multinuclear (H, C,Pt) NMR spectroscopy. DFT (B3LYP/6-31G*/LANL08) and AIM calculations suggest a stronger bonding of hmta with the [PtCl(oxadiazoline)] fragment, in agreement with the experimentally observed reactivity in the ligand exchange (hmta > 7-NOTAA). Replacement of the nitrile by hmta is predicted to be more exothermic than that with 7-NO-TAA, although the activation barriers are similar. Protonation of the non-coordinated N atoms is anticipated to weaken the Pt-N bond and lower the activation barrier for ligand exchange. This effect might help activate these compounds in a slightly acidic environment such as some tumour tissues. Ten of the new compounds were tested for their in vitro cytotoxicity in the human cancer cell lines HeLa and A549. Some of the mononuclear complexes are more potent than cisplatin, and their activity is still high in A549 where cisplatin shows little effect. The dinuclear complexes are inactive, presumably due to their lipophilicity and reduced solubility in water.

Significance: A highly stable heptacene derivative (9) has been synthesized. This compound is stabilized by the thioaryl substituents as well as by the o-dimethylphenyl groups. The only previous reports of functionalized heptacenes contained silylethynyl substituents on the central ring.Comment: The authors utilize the remarkable stability conferred by the thioaryl substituents which protect the central ring from photooxidation. Compound 9 has a small HOMO-LUMO gap of 1.37 V, calculated based on the onset of its longest wavelength absorption. S S Br Br Br Br or O O KI, DMF, reflux O O R R O O 4 R = 4-(t-butyl)phenyl, 65% yield 5 R = 4-(t-butyl)phenylthio, 57% yield 1 2 3 O O R R O O O O R R O O 1. NaBH 4 , THF 2. SnCl 2 , 1,4-dioxane 10% HCl R R R R 4 , 5 6 R = 4-(t-butyl)phenyl 7 R = 4-(t-butyl)phenylthio 4 , 5 8 R = 4-(t-butyl)phenyl 9 R = 4-(t-butyl)phenylthio Br Br Br Br SYNFACTS Contributors: