Hydrolysis of tin(II) neo-pentoxide: syntheses, characterization, and X-ray structures of [Sn(ONep)(2)](infinity), Sn(5)(mu(3)-O)(2)(mu-ONep)(6), and Sn(6)(mu(3)-O)(4)(mu-ONep)(4) where ONep = OCH(2)CMe(3)

The reaction of [Sn(NMe(2))(2)](2) (1) with 4 equiv of HOCH(2)CMe(3) (HONep) leads to the isolation of [Sn(ONep)(2)](infinity) (2). Each Sn atom is four coordinated with mu-ONep ligands bridging the metal centers; however, if the free electrons of the Sn(II) metal center are considered, each Sn center adopts a distorted trigonal bipyramidal (TBP) geometry. Through (119)Sn NMR experiments, the polymeric compound 2 was found to be disrupted into smaller oligomers in solution. Titration of 2 with H(2)O led to the identification of two unique hydrolysis products characterized by single-crystal X-ray diffraction as Sn(5)(mu(3)-O)(2)(mu-ONep)(6) (3) and Sn(6)(mu(3)-O)(4)(mu-ONep)(4) (4). Compound 3 consists of an asymmetrical molecule that has five Sn atoms arranged in a square-based pyramidal geometry linked by four basal mu-ONep ligands, two facial mu(3)-O, and two facial mu-ONep ligands. Compound 4 was solved in a novel octahedral arrangement of six Sn cations with an asymmetric arrangement of mu(3)-O and mu-ONep ligands that yields two square base pyramidal and four pyramidal coordinated Sn cations. These compounds were further identified by multinuclear ((1)H, (13)C, (17)O, and (119)Sn) solid-state MAS and high resolution, solution NMR experiments. Because of the complexity of the compounds and the accessibility of the various nuclei, 2D NMR experiments were also undertaken to elucidate the solution behavior of these compounds. On the basis of these studies, it was determined that while the central core of the solid-state structures of 3 and 4 is retained, dynamic ligand exchange leads to more symmetrical molecules in solution. Novel products 3 and 4 lend structural insight into the stepwise hydrolysis of Sn(II) alkoxides.     

Synthesis of N3- and 2-NH2-substituted 6,7-diphenylpterins and their use as intermediates for the preparation of oligonucleotide conjugates designed to target photooxidative damage on single-stranded DNA representing the bcr-abl chimeric gene

Two 17-mer oligodeoxynucleotide-5'-linked-(6,7-diphenylpterin) conjugates, 2 and 3, were prepared as photosensitisers for targeting photooxidative damage to a 34-mer DNA oligodeoxynucleotide (ODN) fragment 1 representing the chimeric bcr-abl gene that is implicated in the pathogenesis of chronic myeloid leukaemia (CML). The base sequence in the 17-mer was 3'G G T A G T T A T T C C T T C T T5'. In the first of these ODN conjugates (2) the pterin was attached at its N3 atom, via a -(CH2)3OPO(OH)- linker, to the 5'-OH group of the ODN. Conjugate 2 was prepared from 2-amino-3-(3-hydroxypropyl)-6,7-diphenyl-4(3H)-pteridinone 10, using phosphoramidite methodology. Starting material 10 was prepared from 5-amino-7-methylthiofurazano[3,4-d]pyrimidine 4 via an unusual highly resonance stabilised cation 8, incorporating the rare 2H,6H-pyrimido[6,1-b][1,3]oxazine ring system. In the characterisation of 10 two pteridine phosphazenes, 15 and 29, were obtained, as well as new products containing two uncommon tricyclic ring systems, namely pyrimido[2,1-b]pteridine (20 and 24) and pyrimido[1,2-c]pteridine (27). In the second ODN conjugate the linker was -(CH2)5CONH(CH2)6OPO(OH)- and was attached to the 2-amino group of the pterin. In the preparation of 3, the N-hydroxysuccinimide ester 37 of 2-(5-carboxypentylamino)-6,7-diphenyl-4(3H)-pteridinone was condensed with the hexylamino-modified 17-mer. Excitation of 36 with near UV light in the presence of the single-stranded target 34-mer, 5'T G A C C A T C A A T A A G14 G A A G18 A A G21 C C C T T C A G C G G C C3' 1 caused oxidative damage at guanine bases, leading to alkali-labile sites which were monitored by polyacrylamide gel electrophoresis. Cleavage was observed at all guanine sites with a marked preference for cleavage at G14. In contrast, excitation of ODN-pteridine conjugate 2 in the presence of 1 caused oxidation of the latter predominantly at G18, with a smaller extent of cleavage at G15 and G14 (in the double-stranded portion) and G21. These results contrast with our previous observation of specific cleavage at G21 with ruthenium polypyridyl sensitisers, and suggest that a different mechanism, probably one involving Type 1 photochemical electron transfer, is operative. Much lower yields were found with the ODN-pteridine conjugate 3, perhaps as a consequence of the longer linker between the ODN and the pteridine in this case.     

Structure and Biodistribution Relationships of Photodynamic Sensitizers*

Abstract— Photodynamic therapy (PDT) has, during the last quarter century, developed into a fully fledged biomedical field with its own association, the International Photodynamic Association (IPA) and regular conferences devoted solely to this topic. Recent approval of the first PDT sensitizer, Photofrin® (porfimer sodium), by health boards in Canada, Japan, the Netherlands and United States for use against certain types of solid tumors represents, perhaps, the single most significant indicator of the progress of PDT from a laboratory research concept to clinical reality. The approval of Photofrin® will undoubtedly encourage the accelerated development of second-generation photo-sensitizers, which have recently been the subject of intense study. Many of these second-generation drugs show significant differences, when compared to Photofrin®, in terms of treatment times postinjection, light doses and drug doses required for optimal results. These differences can ultimately be attributed to variations in either the quantum efficiency of the photosensitizer in situ, which is in turn affected by aggregation state, localized concentration of endogenous quenchers and primary photophysics of the dye, or the intratumoral and intracellular localization of the photosensitizer at the time of activation with light. The purpose of this review is to bring together data relating to the biodistribution and pharmacokinetics of second-generation sensitizers and attempt to correlate this with structural and electronic features of these molecules. As this requires a clear knowledge of photosensitizer structure, only chemically well-characterized compounds are included, e.g. Photofrin® and crude sulfonated phthal-ocyanines have been excluded as they are known to be complex mixtures. Nonporphyrin-based photosensitizers, e.g. rose bengal and the hypericins, have also been omitted to allow meaningful comparisons to be made between different compounds. As the intracellular distribution of photosensitizers to organelles and other subcellular structures can have a large effect on PDT efficacy, a section will be devoted to this topic.     

BIOLOGICAL ACTIVITIES OF PHTHALOCYANINES. XIII. THE EFFECTS OF HUMAN SERUM COMPONENTS ON THE in vitro UPTAKE AND PHOTODYNAMIC ACTIVITY OF ZINC PHTHALOCYANINE

Abstract— The effect of human serum components on the photodynamic activity of zinc phthalocyanine (ZnPc) toward Chinese hamster fibroblasts (lineV–79) was studied. Photodynamic activities were correlated with cellular uptake of radiolabeled [⁶⁵Zn]ZnPc, which allowed corrections to be made for the amount of sensitizer present in the cells at the time of irradiation and to express photodynamic efficiences on a cellular dye concentration basis. All serum components, with the exception of high-density lipoproteins, inhibit uptake of ZnPc byV–79 cells, when compared to incubation of ZnPc with the same cells in serum-free medium. High-density lipoproteins increased ZnPc uptake by 23%, but the photodynamic efficiency corrected for the cellular ZnPc concentration was unaffected. Very low-density lipoprotein and globulins decreased ZnPc cell uptake but likewise did not affect the cellular photodynamic efficiency of the dye. In contrast low-density lipoprotein and albumin, while inhibiting ZnPc cell uptake, increased the cellular photodynamic efficiency of ZnPc, suggesting that these proteins facilitate localization of the dye at cellular targers sensitive to photodynamic damage and vital to cell survival. We conclude from these results that association of ZnPc with serum components can have important, and widely differing, effects on both degree of uptake and cellular distribution of the photosensitizer.     

Chemistry of a novel family of tridentate alkoxy tin(II) clusters

The chemical interconversions observed for a novel family of trihydroxymethyl ethane (THME-H(3)) ligated Sn(II) compounds have been determined using single-crystal X-ray and (119)Sn NMR experiments. (mu-THME)(2)Sn(3) (1) was isolated from the reaction of 3 equiv of [Sn(NR(2))(2)](2) (R = SiMe(3)) with 4 equiv of THME as a unique trinuclear species capped above and below the plane of Sn atoms by two THME ligands. Upon reaction with "Sn(NR(2))(2)", compound 1 rearranged to yield another novel molecule [(mu-THME)Sn(2)(NR(2))](2) (2). Compound 2 could also be formed directly from the stoichiometric mixture of THME-H(3) and [Sn(NR(2))(2)](2). Further studies revealed that 1 would also rearrange in the presence of Sn(OR)(2) to form [(mu-THME)Sn(2)(mu-OR)](2) [OR = OMe (3), OCH(2)Me (4), OCH(2)CH(Me)CH(2)CH(3) (5), OCH(2)CMe(3) (6, ONep), OC(6)H(5) (7, not structurally characterized), OC(6)H(4)Me-3 (8), OC(6)H(4)Me-2 (9), OC(6)H(3)(Me)(2)-2,6 (10), OC(6)H(3)(CHMe(2))(2)-2,6 (11). Additionally, 3-11 could by synthesized from the reaction of 2 and the appropriate H-OR. (119)Sn solution NMR studies of 2-11, in THF-d(8), indicate that an equilibrium between the parent complex and its disassociation products (1 and the free parent Sn alkoxy or amide precursor) exists at room temperature. This is a likely reason behind the ease of interconversion observed for 1. The generality of this exchange was further verified through the reaction of 1 with [Ti(mu-ONep)(ONep)(3)](2), which led to the isolation of (mu-ONep)(2)Sn(3)(mu-THME)(2)Ti(ONep)(2) (12). For 12, the solid-state structure was maintained in solution with no indication of an equilibrium.     

A comparative semi-empirical study of the effect of ring ortho-substitution on the conformation of diphenylamine

An extensive theoretical study of the structural and energy properties of diphenylamine (DPA) and derivatives was carried out. The effect of ring substitution on geometrical parameters, inversion barriers and ionisation potentials was investigated for rings containing methyl, methoxy and chloro groups. The dihedral angles between phenyl rings and pyramidality of the nitrogen atom were also studied. Results were compared to the optimised geometry of the unsubstituted DPA. Calculations were carried out using the AM1 semi-empirical method.     

Non‐mutagenic organic pigment intermediates. I. 3,3′‐Dipropoxybenzidine

Crystals of the title compound, C₁₈H₂₄N₂O₂, were grown from ethanol by slow evaporation and the structure has been determined. The mol­ecule resides on a crystallographic inversion center and the bi­phenyl moiety is essentially planar. The structure forms an infinite two‐dimensional array of N—H⋯π(arene) interactions parallel to the (101) direction.     

Aminoisoquinolines as colorimetric Hg sensors: the importance of molecular structure and sacrificial base

Here it is shown that 3-phenyl-2-amino isoquinoline acts as a simple mercury sensor. It is simple to synthesize. The molecule requires base/buffer to bind in a 1:1 stoichiometry with mercury ion, however. Otherwise, it acts as a sacrificial base, presumably to pick up a proton liberated during binding. This binding is characterized quantitatively.