Chemistry

The bicyclic hexaamine "cage" ligand Me 8 tricosaneN 6 (1,5,5,9,13,13,20,20octamethyl-3,7,11,15,18,22-hexaazabicyclo[7.7.7]tricosane) is capable of encapsulating octahedral metal ions, yet its expanded cavity allows the complexed metal to adopt a variety of geometries comprising either hexadentate or pentadentate coordination of the ligand. When complexed to Cu II the lability of the metal results in a dynamic equilibrium in solution between hexadentate-and pentadentate-coordinated complexes of Me 8 tricosa-neN 6 . Both [Cu(Me 8 tricosaneN 6 )](ClO 4 ) 2 (6-coordinate) and [Cu(Me 8 tricosane-N 6 )](S 2 O 6 ) (5-coordinate) have been characterized structurally. In weak acid (pH 1) a singly protonated complex [Cu(HMe 8 tricosaneN 6 )] 3+ has been isolated that finds the ligand binding as a pentadentate with the uncoordinated amine being protonated. visÀNIR and electron paramagnetic resonance (EPR) spectroscopy show that the predominant solution structure of [Cu(Me 8 tricosaneN 6 )] 2+ at neutral pH comprises a five-coordinate, square pyramidal complex. Cyclic voltammetry of the square pyramidal [Cu(Me 8 tricosaneN 6 )] 2+ complex reveals a reversible Cu II/I couple. All of these structural, spectroscopic, and electrochemical features contrast with the smaller cavity and well studied "sarcophagine" (sar, 3,6,10,13,16,19-hexaazabicyclo[6.6.6]eicosane) Cu II complexes which are invariably hexadentate coordinated in neutral solution and cannot stabilize a Cu I form.

The cytotoxicity of the metallointercalators, [Pt(5,6-dimethyl-1,10-phenanthroline)(trans-1R,2Rdiaminocyclohexane)] 2+ ([56MERR]) and [Pt(5,6-dimethyl-1,10-phenanthroline)(trans-1S,2Sdiaminocyclohexane)] 2+ ([56MESS]), towards A549 human lung cancer cells was examined using the 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assay. The IC 50 value obtained following exposure of A549 cells to [56MESS] for 4 h was approximately three times smaller than that obtained when [56MERR] was administered under the same conditions, indicating that the former complex displayed greater cytotoxicity. Both IC 50 values were greater than that obtained after exposure of A549 cells to cisplatin, demonstrating that the latter compound was the most cytotoxic of the three examined. Microprobe synchrotron radiation X-ray fluorescence (SR-XRF) analyses of metallointercalator-treated A549 cells showed that platinum became localised in DNA-rich regions of the nucleus. In contrast, when the same cells were treated with cisplatin the metal became distributed throughout the cell. Determination of the maximum concentration of platinum present inside the cells using graphite furnace atomic absorption spectrophotometry (GFAAS) of platinum-treated cells suggested that there was greater uptake of [56MERR] compared to [56MESS] by the A549 cells, and that platinum uptake did not account for the greater toxicity of [56MESS], as assessed by the MTT assay. Electrospray ionization mass spectrometric (ESI-MS) and circular dichroism (CD) spectroscopic studies of solutions containing either [56MERR] or [56MESS], and a duplex hexadecamer molecule, showed the two metallointercalators displayed very similar affinity towards the nucleic acid. Overall these results indicate that the difference in cytotoxicity of the two platinum metallointercalators is probably the result of variations in their interactions with other cellular components. † Electronic supplementary information (ESI) available. See

As part of a program of preparing metal complexes which exhibit unique affinities towards different DNA
structures, we have synthesised the novel Schiff base complex N,N’-bis-4-(hydroxysalicylidine)mesodiphenylethylenediaminenickel(
II) (4), via the reaction of meso-1,2-diphenylethylenediamine and 2,4-
dihydroxybenzaldehyde. This compound was subsequently reacted with 1-(2-chloroethyl)piperidine or
1-(2-chloropropyl)piperidine, to afford the alkylated complexes N,N’-bis-(4-((1-(2-ethyl)piperidine)oxy)-
salicylidine)meso-1,2-diphenylethylenediaminenickel(II) (5) and N,N’-bis-(4-((1-(3-propyl)piperidine)oxy)-
salicylidine)meso-1,2-diphenylethylenediaminenickel(II) (6), respectively. These complexes were characterised
by microanalysis and X-ray crystallography in the solid state, and in solution by 1H and 13C NMR
spectroscopy. Electrospray ionisation mass spectrometry (ESI-MS) was used to confirm the identity of (5)
and (6). The affinities of (5) and (6) towards a discrete 16 mer duplex DNA molecule, and examples of both
tetramolecular and unimolecular DNA quadruplexes, was explored using a variety of techniques. In
addition, the affinity of two other complexes (2) and (3), towards the same DNA molecules was examined.
Complexes (2) and (3) were prepared by methods analogous to those which afforded (5) and (6), however
1,2-phenylenediamine was used instead of meso-1,2-diphenylethylenediamine in the initial step of the
synthetic procedure. The results of ESI-MS and DNA melting temperature measurements suggest that (5)
and (6) exhibit a lower affinity than (2) and (3) towards the 16 mer duplex DNA molecule, while circular
dichroism (CD) spectroscopy suggested that none of the four complexes had a major effect on the conformation
of the nucleic acid. In contrast, ESI-MS and CD spectroscopy suggested that both (5) and (6)
show significant binding to a tetramolecular DNA quadruplex. The results of ESI-MS and Fluorescence
Resonance Energy Transfer (FRET) assays indicated that (5) and (6) did not bind as tightly to a unimolecular
DNA quadruplex, although both complexes had a major effect on the CD spectrum of the latter. These
results highlight that the presence of the meso-1,2-diphenylethylenediamine moiety in metal complexes
of this type may provide a general method for instilling selectivity for some DNA quadruplexes over
dsDNA.

Two different series of nickel Schiff base complexes were prepared as part of a study aimed at discovering new compounds with high affinity and selectivity for quadruplex DNA (qDNA). The new complexes were prepared by modification of a literature method for synthesising N,N'-bis-(4-((1-(2-ethyl)piperidine)-oxy)salicyli-dene)phenylenediaminenickel(II) (complex (1)). For Series 1 complexes, the phenylenediamine head group of the literature complex was replaced with ethylenediamine, phenanthrenediamine, R,R-and S,S-diamino-cyclohexane. These complexes, as well as an asymmetric molecule featuring a naphthalene moiety on one side and a single ethyl piperidinyl salicylidene group on the other, were prepared in order to examine the effect of varying the number and position of aromatic groups on DNA binding. Series 2 complexes were isomers of those in Series 1, in which pendant ethyl piperidine groups were located at different positions. All new complexes were characterised by 1D and 2D NMR spectroscopic methods alongside microanalysis and ESI-MS. In addition, the solid state structures of eight new complexes were determined using single crystal X-ray diffraction methods. N,N'-Bis-(4-((1-(2-ethyl)piperidine)oxy)-salicylidine)diaminophenanthrenenickel(II) (9), was shown by ESI-MS, CD spectroscopy and UV melting studies to exhibit a greater affinity towards, and ability to stabilise, dsDNA than all other complexes in the first series. ESI-MS revealed (9) to have a strong tendency to form a 1 : 1 complex with the tetramolecular, parallel qDNA molecule Q4, however it exhibited low affinity towards the parallel unimolecular qDNA molecule Q1. The enantiomeric complexes (5) and (7), featuring R,R-and S,S-diaminocyclohexane moieties, respectively, showed similar binding profiles towards all DNA molecules investigated, whereas the asymmetric complex (11), exhibited very low DNA affinity in all cases. Series 2 complexes showed very similar DNA affinity and selectivity to their isomeric counterparts in Series 1. For example, (14) and (15), both of which contain a phenylenediamine head group, showed higher affinity towards D2, Q1 and Q4, than any of the other Series 2 complexes. In addition, complex (21), which contains a meso-1,2-diphenylethylenediamine moiety, interacted strongly with Q4, but not D2 or Q1. This observation was very similar to that made previously for the isomeric complex (3).

Diversity-directed synthesis based on the cascade allylation chemistry of indigo, with its embedded 2,2’-diindolic core, has resulted
in rapid access to new examples of the hydroxy-8a,13-dihydroazepino[1,2-a:3,4-b']diindol-14(8H)-one skeleton in up to 51% yield.
Additionally a derivative of the novel bridged heterocycle 7,8-dihydro-6H-6,8a-epoxyazepino[1,2-a:3,4-b']diindol-14(13H)-one
was produced when the olefin of the allylic substrate was terminally disubstituted. Further optimisation also produced viable onepot
syntheses of derivatives of the spiro(indoline-2,9'-pyrido[1,2-a]indol)-3-one (65%) and pyrido[1,2,3-s,t]indolo[1,2-
a]azepino[3,4-b]indol-17-one (72%) heterocyclic systems. Ring-closing metathesis of the N,O-diallylic spiro structure and subsequent
Claisen rearrangement gave rise to the new (1R,8aS,17aS)-rel-1,2-dihydro-1-vinyl-8H,17H,9H-benz[2',3']pyrrolizino-
[1',7a':2,3]pyrido[1,2-a]indole-8,17-(2H,9H)-dione heterocyclic system.