The first systematic electrochemical study by cyclic voltammetry (CV) and rotating-disk electrode (RDE) of the changes in redox properties of covalent fullerene derivatives (2-11) as a function of increasing number of addends is reported. Dialkynylmethanofullerenes 2 4 undergo multiple, fullerene-centered reduction steps at slightly more negative potentials than C60 (1; see Table and Fig.1). The two C-spheres in the dumbbell-shaped dimeric fullerene derivative 4 show independent, identical redox characteristics. This highlights the insulating character of the sp.'-C-atoms in methanofullerenes which prevent through-bond communication of substituent effects from the methano bridge to the fullerene sphere. In the series of mono-through hexakis-adducts 511, formed by tether-directed remote functionalization, reductions become increasingly difficult and more irreversible with increasing number of addends (see Table and Fig.2). Whereas, in 0 . 1~ Bu,NPF,/CH2Cl2, the first reduction of mono-adduct 5 occurs reversibly at -1.06 V vs. the ferroceneiferricinium couple (Fc/Fc+), hexakis-adduct 11 is reduced irreversibly only at -1.87 V. Hence, with incremental functionalization of the fullerene, the LUMO of the remaining conjugated framework is raised in energy. Reduction potentials are also dependent on the relative spatial disposition of the addends on the surface of the fullerene sphere. Observed UVjVIS spectral changes and changes in the chemical reactivity along the series 5511 are in accord with the results of electrochemical measurements. Further, with increasing number of addends, the oxidation of derivatives 5-11 becomes more reversible. Whereas oxidations are increasingly facilitated upon going from mono-adduct 5 (f1.22 V) to tris-adduct 7 (+0.90 V), they occur at nearly the same potential (+0.95 to +0.99 V) in the higher adducts 8-11. This indicates that the oxidations occur in these compounds at a common sub-structural element, for which a 'cubic' cyclophane is proposed (see Fig. 3 ) . This sub-structure is fully developed in hexakis-adduct 11.

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6H-Isoindolo[2,1-a]indoles (5, 7, 10, 13), 5,6-dihydroindolo[2, 1-a]isoquinolines (20, 21), and 6,7-dihydro-5H-benzo[c]azepino[2, 1-a]indoles (23, 25, 27, 30) have been prepared as melatonin analogues to investigate the nature of the binding site of the melatonin receptor. The affinity of analogues was determined in a radioligand binding assay using cloned human mt(1) and MT(2) receptor subtypes expressed in NIH 3T3 cells. Agonist and antagonist potency was measured using the pigment aggregation response of a clonal line of Xenopus laevis melanophores. The 2-methoxyisoindolo[2, 1-a]indoles (7a-d) showed much higher binding affinities than the parent isoindoles (5a-e), and whereas 7a-c were agonists in the functional assay, 7d and 5a-e were antagonists. The 2-ethoxyisoindolo[2,1-a]indoles (10a-d) showed reduced binding affinities compared to their methoxy analogues, while the 5-chloro derivative 13 showed a considerable reduction in binding affinity and potency compared to 7a. The 10-methoxy-5,6-dihydroindolo[2, 1-a]isoquinolines (21a-c) had higher binding affinities than the corresponding parent indoloisoquinolines (20a-c) in the human receptor subtypes, and the parent compounds were antagonists whereas the 10-methoxy derivatives were agonists in the functional assay. The N-cyclobutanecarbonyl derivatives of both the parent (20d) and 10-methoxyl (21d) series had similar binding affinities and were both antagonists with similar potencies. The 11-methoxy-6, 7-5H-benzo[c]azepino[2,1-a]indoles (25a-d) had higher binding affinities than the corresponding parent compounds (23a-d) at the MT(2) receptor but similar affinities at the mt(1) site; all of the compounds were antagonists in the functional assay. Changing 11-methoxy for 11-ethoxy decreased the binding affinity slightly, and this was more evident at the MT(2) receptor. All of the derivatives investigated had either the same or a greater affinity for the human MT(2) receptor compared to the mt(1) receptor (range 1:1-1:132). This suggests that the mt(1) and MT(2) receptor pockets differ in their ability to accommodate alkyl groups in the indole nitrogen region of the melatonin molecule. Two compounds (7c and 25c) were tested in functional assays on recombinant mt(1) and MT(2) melatonin receptors. Compound 7c is a potent agonist with some selectivity (44-fold) for the MT(2) receptor, while 25c is an MT(2)-preferring antagonist. Increasing the carbon chain length between N-1 of indole and the 2-phenyl group from n = 1 through n = 3 leads to a fairly regular decrease in the binding affinity, but, remarkably, when n = 3, it converts the methoxy compounds from melatonin agonists to antagonists. The Xenopus melatonin receptor thus cannot accommodate an N-n-alkyl chain attached to a 2-phenyl substituent with n > 2 in the required orientation to induce or stabilize the active receptor conformation.

It is amazing what three carbons can do! Nature, industry, and chemists working in academia continue to explore the cyclopropane moiety from various perspectives, among them biological activity, reactivity, and synthetic methodology. Breathtaking multiple cyclopropane ring structures such as 1 and 2 have recently been prepared and represent milestones in the field of small‐ring chemistry.

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A range of lipo- and hydrophilic derivatives of the new class of octaalkynyl tetra-[6,7]-quinoxalinoporphyrazines (TQuiPors), analogues of the naphthalocyanines, were prepared in two steps starting from functionalised hexa-1,5-diyne-3,4-diones. Divalent zinc and magnesium ions were introduced into the macrocyclic core. Whereas the triisopropylsilyl-, 3,5-di-tert-butylphenyl- and 4-triisopropylsilyloxyphenyl-terminated acetylenic TQuiPors are lipophilic and hence soluble in standard organic solvents, a polyethylene glycol-substituted derivative was found to dissolve in DMSO as well as in ethanol/water mixtures. The new chromophores are characterised by intense UV/Vis/NIR absorptions, most notably by bands at 770 nm with extinction coefficients exceeding 500 000 M(-1) cm(-1). With a view to possible photodynamic therapy applications, the potency of the chromophores to sensitise the formation of singlet oxygen was examined, both qualitatively using a 1,3-diphenylisobenzofuran assay, and quantitatively by the determination of the singlet oxygen quantum yields. It was found that all TQuiPors produce singlet oxygen when irradiated in the presence of air. In particular, the octaalkynyl Zn-TQuiPor generates singlet oxygen with a quantum yield of 56 %, thereby rivalling, and, in conjunction with its absorption profile, even exceeding the standards set by established PDT agents. The photostabilities of the TQuiPors were assessed and generally found to be satisfactory, but dependent on the solvent and the wavelength of the incident light.

Abstract:The syntheses of the first organometallic mono-and dinuclear platinum complexes bearing the tetraethynylethene unit as an q'-ligand are reported. Structural characterization of two of the trans o-bis(acety1ide) derivatives by X-ray crystallography reveals coplanarity of the acetylenic n-ligands and indicates possible electronic delocalization across the metal center. This notion is further supported by comparing the electronic absorption spectra of the platinum-containing compounds with those of related tetraethynylethene derivatives without metals. The solidstate structure of a dinuclear complex with two iodoplatinum fragments at-