Previous structural analyses of diphosphoinositol polyphosphates in biological systems have relied largely on NMR analysis. For example, in Dictyostelium discoideum, diphosphoinositol pentakisphosphate was determined by NMR to be 4- and/or 6-PPInsP5, and the bisdiphosphoinositol tetrakisphosphate was found to be 4, 5-bisPPInsP4 and/or 5,6-bisPPInsP4 [Laussmann, Eujen, Weisshuhn, Thiel and Vogel (1996) Biochem. J. 315, 715-720]. We now describe three recent technical developments to aid the analysis of these compounds, not just in Dictyostelium, but also in a wider range of biological systems: (i) improved resolution and sensitivity of detection of PPInsP5 isomers by microbore metal-dye-detection HPLC; (ii) the use of the enantiomerically specific properties of a rat hepatic diphosphatase; (iii) chemical synthesis of enantiomerically pure reference standards of all six possible PPInsP5 isomers. Thus we now demonstrate that the major PPInsP5 isomer in Dictyostelium is 6-PPInsP5. Similar findings obtained using the same synthetic standards have been published [Laussmann, Reddy, Reddy, Falck and Vogel (1997) Biochem. J. 322, 31-33]. In addition, we show that 10-25% of the Dictyostelium PPInsP5 pool is comprised of 5-PPInsP5. The biological significance of this new observation was reinforced by our demonstration that 5-PPInsP5 is the predominant PPInsP5 isomer in four different mammalian cell lines (FTC human thyroid cancer cells, Swiss 3T3 fibroblasts, Jurkat T-cells and Chinese hamster ovary cells). The fact that the cellular spectrum of diphosphoinositol polyphosphates varies across phylogenetic boundaries underscores the value of our technological developments for future determinations of the structures of this class of compounds in other systems.

Silver(1) perchlorate or nitrate react readily with bis(diphenylphosphany1)-o-carborane to give the complexes [AgX((PPh2)2C2BloHlo)1 [X = C104 (l), NO3 (2)]. The perchlorate ligand is weakly bound to the silver atom and thus can be displaced by other ligands affording the three-coordi- (13), NC4H8 (14)]. The crystal structures of 11 and 12 have been established by X-ray crystallography. In both complexes the silver(1) atoms exhibit tetrahedral coordination by two phosphorus and two nitrogen or two sulfur atoms, respectively. In our studies with o-carborane derivatives as ligands we have reported on the synthesis of unusual high-coordinated gold(1) complexes with the bis(diphenylphosphany1)-o-carborane ligand[I0l. We have now extended our studies to silver(1) complexes and prepared a variety of three-and fourcoordinated derivatives where the diphosphine acts as a chelating ligand. The crystal structures of two mixed tetrahedral complexes are described here. Synthesis and Properties of the ComplexesBis(diphenylphosphany1)-o-carborane reacts with one equivalent of AgC104 in diethyl ether or with AgN03 in acetone at room temperature to give the colourless complexes 1 and 2, respectively (see Scheme 1). In these complexes the rigidity of the o-carborane moiety causes the chelating mode of thc diphosphane ligand to be preferred to the bridging mode.The reactivity of complex 1 with monodentate ligands has been studied. The reaction of 1 in dichloromethane with tertiary phosphanes leads to the three-coordinated complexes 3 or 4. These complexes can also be obtained by the reaction of [Ag(OC103)PR3] with the diphosphane ligand. Other monodentate ligands with arsenic, nitrogen, or sulfur donor atoms have been used to synthesize a variety of three-coordinated complexes of silver (1); the ligands used were tripheiiylarsane, triphenylphosphane sulfide, picolinic and quinoleic acid, whereby the latter act as monodentate ligands and cannot be deprotonated by treating the complexes with Na2C03 (Scheme 1).The use of bidentate ligands has allowed us to prepare four-coordinated derivatives, and we have again chosen ligands with various donor centres. The reaction of 1 with the bis(diphenylphosphany1)-o-carborane ligand gives the homoleptic diphosphane complex 9, also obtained by reaction of two equivalents of the ligand with AgC104; whereas with nitrogen or sulfur donor ligands such as bipy, phen, (SPPh2)CH2, or dithiocarbamates the mixed four-coordinated complexes 10-14 are obtained.

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The title compound contains three independent formula units. There is a large spread of values for chemically equivalent dimensions, notably in the cations, which display tetrahedral coordination at silver; Ag–N 2.228(4)–2.315(5) [av.2.266] Å, N–Ag–N 104.6(2)–115.7(2) [av. 109.6]°.

The title compound contains three independent formula units. There is a large spread of values for chemically equivalent dimensions, notably in the cations, which display tetrahedral coordination at silver; Ag-Ν 2.228(4)-2.315(5) [av. 2.266JÄ, N-Ag-N 104.6(2)-115.7(2) [av. 109.6]°.

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