C-scorpionates

Scheme 2.3 Examples of transition metal catalyst precursors for the peroxidative oxidation of alkanes, bearing (a) a C-scorpionate [16-20], (b) an azoderivative of a 8-diketone [21], (c) an aminopolyalcohol derivative (tea = deprotonated form of triethanolamine, Hjtea) [33, 34], and (d) a benzene dicarboxylate [33, 34] hgand.

The BV oxidation by aqueous H2O2 in 1,2-dichloroethane of cyclic and linear ketones to the corresponding lactones and esters (Scheme 22.5) is catalyzed by Re(ni or IV) complexes bearing C-scorpionate or pyrazole ligands, which conceivably allow the involvement of coordinative unsaturation at the metal in view of their lability [Hpz, t] - or j) -HC(pz)3 toward lower denticity] and/or proton-transfer steps on account of their basic character—features that are favorable to the occurrence of oxidation catalysis with H2O2 [9]. 

Saladino R, Crestini C, Costanzo G, DiMauro E (2005) On the Prebiotic Synthesis of Nucle-obases, Nucleotides, Oligonucleotides, Pre-RNA and Pre-DNA Molecules. 259 29-68 Santos I, Paulo A, Correia JDG (2005) Rhenium and Technetium Complexes Anchored by Phosphines and Scorpionates for Radiopharmaceutical Applications. 252 45-84 Santos M, see Szathmdry E (2005) 259 167-211... 

A major advance in the intermolecular C-H insertion chemistry of ethyl diazoacetate was the discovery that copper and silver scorpionate catalysts gave very clean transformations.50-61 The regioselectivity of the C-H insertion was... 

Uchimura M, Sandeauz R, Larroque C (1999) The enzymatic detoxifying system of a native Mediterranean scorpion fish is affected by Caulerpa taxifolia in its environment. Environ Sci Technol 33 1671-1674... 

Milnes, J.T., Dempsey, C.E., Ridley, J.M., Crociani, O., Arcangeli, A., Hancox, J.C. and Witchel, H.J. (2003) Preferenhal closed channel blockade of hERG potassium currents by chemically synthesised BeKm-1 scorpion toxin. FEBS Letters, 547, 20-26. 

The three-dimensional structural architecture of plant defensins is exemplified by the structure of Rs-AFP, ° which comprises an N-terminal /3-strand followed by an ct-helix and two /3-strands (/3a/3/3 configuration). The /3-strands form a triple-stranded antiparallel /3-sheet. The three-dimensional structure is stabilized by three disulfide bonds. In general, in plant defensins two disulfide bonds form between the ct-helix and the central /3-strand. A third disulfide bond stabilizes the structure by linking the /3-strand after the helix to the coiled part after the ct-helix. This motif is called the cysteine-stabilized a/3-motif (CSa/3)" and also occurs in toxins isolated from insects, spiders, and scorpions.The fourth disulfide bond links the C-terminal end of the peptide with the N-terminal /3-strand. Two plant defensins, PhDl and PhD2, feature a fifth disulfide bond and have been proposed to be the prototypes of a new subclass within plant defensins." As a result of these structural features the global structure of plant defensins is notably different from o //3-thionins, which is one of the reasons for the different nomenclature. The structures of plant defensins Rs-AFP ° and NaDf are shown in Figure 6, where they are compared to the thionin /3-purothionin and the structurally more related drosomycin and charybdotoxin. ... 

Figures Comparison of the plant defensin structures Rs-AFP((a), gray, 1ayj)and NaDI ((b), green, 1mr4) with/3-purothionin ((c), magenta, 1 bhp) reveals the structural differences between plant defensins and a//3-thionins. The architecture resembles that of insect defensins, for example, drosomycin ((d), pink, 1 myn) or the scorpion toxin charybdotoxin ((e), yellow, 2crd). The structural similarities become clear in the overlay of Rs-AFP, NaDI, and drosomycin ((f), colors as before).

L. D. Possani R. C. Rodriguez de la Vega, Scorpion Venom Peptides. In Handbook of Biologically Active Peptides] J. Kastin, Ed. Elsevier Burlington, MA, 2006 p 339. 

Hybrid scorpionate/cyclopentadienyl-Mg (63) and -Zn (64,65) complexes were structurally characterized and reported to catalyze the formation of PLAs with medium molecular weights and narrow polydispersities [85]. Among them, the magnesium complex 63 is much more active than the others, giving a polymerization of L-lactide in toluene at 90 °C with 97% conversion in 2.5 h. However, it takes 30 h for zinc complexes 64 and 65 to reach similar results under the same conditions. Some representative structures of magnesium and zinc complexes are summarized in Table 2 as they display closely related ROP activity of lactide, and often stmcrnrally similar ligand systems are employed to construct these initiators. 

Culver, David C. (1982). Cave Life Evolution and Ecology. Cambridge Harvard University Press, 59. Jackman, Jack. (1997). A Field Guide to Spiders and Scorpions of Texas. Houston Gulf Publishing Company, 92. 

Crossley A. C. and Waterhouse D. F. (1969) The ultrastructure of a pheromone-secreting gland in the male scorpion-fly Harpobittacus australis (Bittacidae Mecoptera). Tissuse Cell 2, 273-294. 

Lu, D., Pava-Ripoll, M., Li, Z., and Wang, C. (2008). Insecticidal evaluation of Beauveria bassiana engineered to express a scorpion neurotoxin and a cuticle degrading protease. Applied Microbiology and Biotechnology, 81, 515-522. 

The intermolecular C-H insertion of alkanes is very chemoselective, as is illustrated by the reaction with 2-methylbutane [4]. The only C-H transformation observed occurs at the methine site to form 21 in 68 % ee. This result is very different from the rhodium carboxylate-catalyzed reactions of ethyl diazoacetate with 2-methylbutane, which gives rise to all four C-H insertion products [16], Improved regioselectivity has recently been achieved in the intermolecular C-H insertion chemistry of ethyl diazoacetate by using either copper [17] or silver [18] scorpionate catalysts, but enantioselective versions of these reactions are not known. 

Figure 17. Schematic diagrams of some representative topologically chiral proteins.79 (a) Condensed schematic drawing of the L subunit of the quinoprotein TV-MADH. The looped line represents the polypeptide backbone with N and C terminals. Cysteine (or half-cystine) residues are numbered, and their a-carbons are indicated by filled circles. Intrachain disulfide bonds are shown as dashed lines joining a pair of filled circles. The heavy line symbolizes an intrachain cofactor link, (b) Chromatium high potential iron protein (HiPIP), one of several Fe4S4 cluster-containing proteins, (c) Toxin II from the scorpion Androctonus australis Hector. Reprinted with permission from C. Liang and K. Mislow, J. Math. Chem. 1994,15,245. Copyright 1994, Baltzer Science Publishers.

Toolson, E.C. and Hadley, N.F. (1979). Seasonal effects on cuticular permeability and epicuticular lipid composition in Centruroides sculpturatus Ewing 1928 (Scorpiones Buthidae)../. Comp. Physiol. B, 129, 319-325. 

Toolson, E.C., White, T. R. and Glaunsinger, W. S. (1979). Electron paramagnetic resonance spectroscopy of spin-labelled cuticle of Centruroides sculpturatus (Scorpiones Buthidae) correlation with thermal effects on cuticular permeability. 

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