Copper and iron interactions with angiotensin-converting enzyme inhibitors. A study by fast-atom bombardment tandem mass spectrometry

Fast atom bombardment, combined with high-energy collision-induced tandem mass spectrometry, has been used to investigate gas-phase metal-ion interactions with captopril, enalaprilat and lisinopril, all angiotensin-converting enzyme inhibitors.Suggestions for the location of metal-binding sites are presented. For captopril, metal binding occurs most likely at both the sulphur and the nitrogen atom. For enalaprilat and lisinopril, binding preferably occurs at the amine nitrogen. Copyright 1999 John Wiley & Sons, Ltd.     

Aromatic Polyhedral Hydroxyborates: Bridging Boron Oxides and Boron Hydrides

No explosion , but per-B-hydroxylation occurs if the icosahedral boron hydrides [closo-B₁₂H₁₂]²⁻ (see picture), [closo-CB₁₁H₁₂]⁻, or closo-1,12-(CH₂OH)₂-1,12-C₂B₁₀H₁₀ are refluxed in 30 % hydrogen peroxide. Thus, the three isoelectronic species [closo-B₁₂(OH)₁₂]²⁻, [closo-1-H-1-CB₁₁(OH)₁₁]⁻, and closo-1,12-H₂-1,12-C₂B₁₀(OH)₁₀ were obtained. ○=BH, ○=BOH.     

Synthesis and structural characterization of symmetrical closo-4,7-I2-1,2-C2B10H10 and [(CH3)3NH][nido-2,4-I2-7,8-C2B9H10

The boron-atom insertion reaction of nido-9,11-I(2)-7,8-C(2)B(9)H(9)(2-), with the HBCl(2):SMe(2) complex yields closo-4,7-I(2)-1,2-C(2)B(10)H(10), 1, in excellent yield. Although the two boron atoms (B3 and B6) nearest to the carbon atoms in 1 are equally available for attack by nucleophiles, the boron-degradation reaction of 1 with alkoxide ion occurs only at the B6 vertex, yielding regioselectively [(CH(3))(3)NH][nido-2,4-I(2)-7,8-C(2)B(9)H(10)], 2. The molecular structures of 1 and 2 have been determined by X-ray diffraction studies. Crystallographic data are as follows. For 1, monoclinic, space group P2(1)/n, a = 6.9199(19) Angstroms, b = 23.9560(7) Angstroms, c = 7.2870(2) Angstroms, beta = 94.081(4) degrees, V = 1204.9(6) Angstroms(3), Z = 4, rho(calcd) = 2.18 g cm(-3), R = 0.020, R(w) = 0.0610; for 2, orthorhombic, space group Pca2(1), a = 14.1141(7) Angstroms, b = 7.0276(4) Angstroms, c = 16.4602(9) Angstroms, V = 1632.7(15) Angstroms(3), Z = 4, rho(calcd) = 1.81 gcm(-3), R = 0.022, R(w) = 0.0623.     

Synthesis, structure, and reactivity of closo-2,3,4,5,6,7,8,9,10,11-decahydroxy-1,12-bis(sulfonic acid)-1,12-dicarbadodecaborane(12).

The reaction of closo-1,12-bis(lithio)-1,12-dicarbadodecaborane(12) (1,12-bis(lithio)-p-carborane) with SO(2) formed closo-1,12-bis(lithiosulfinato)-p-carborane (10) in nearly quantitative yield. The latter was converted to closo-1,12-bis(sulfinic acid)-p-carborane (13) via H(+)-exchange. The corresponding 1,12-bis(sulfonic acid) derivative of p-carborane (12) was obtained in high yield by treating 10 with SO(2)Cl(2) and subsequent AlCl(3) mediated hydrolysis of the closo-1,12-bis(chlorosulfonyl)-p-carborane intermediate. The exhaustive oxidation of 12 in hot aqueous H(2)O(2) (30%) afforded B-decahydroxy-1,12-bis(sulfonic acid)-p-carborane (15) in 40% yield. As a byproduct, closo-B-decahydroxy-1-sulfonic acid-p-carborane (14) was formed. Both 14 and 15 were also obtained from the hydroxylation of 10 and 13. Compound 14 was obtained directly in 88% yield by heating 1-sulfinic acid-p-carborane (17) in H(2)O(2) (30%). Compound 17 was synthesized from diphenylmethylsilyl-protected p-carborane by using the method employed in the synthesis of 13. The X-ray structures of 15, its disodium salt, and its dipotassium salt are presented and discussed. Exhaustive methylation of 15 with methyl triflate furnishes closo-B-decamethoxy-1,12-bis(methyl sulfonate)-p-carborane (20). The characterization of closomer 20 also includes its crystal structure determination.