Characterization of iridoids by fast atom bombardment mass spectrometry followed by collision-induced dissociation of

Fast atom bombardment mass spectra of a series of naturally occurring and synthetically modified iridoid glycosides were studied using lithium cationization and collision-induced dissociation of the resulting [M+Li]+ ions. Lithium cationization leads to the unambiguous determination of the molecular masses of these compounds. Collision-induced dissociation of the lithiated molecular ions give valuable structural information regarding the nature of the substituent on both the aglycone and the sugar moieties. The characteristic fragmentation pathways identified are (1) elimination of neutral molecules comprising the substituents on either the aglycone or sugar moieties, (2) formation of lithiated aglycone and their fragment ions, (3) formation of lithiated sugar and their fragment ions, (4) fragmentation corresponding to the cleavage of the aglycone or sugar ring and (5) fragmentation characteristic of the substituents present in either the aglycone or sugar parts of the molecule. Elimination of two acyloxy radicals from the lithiated molecular ion is a characteristic fragmentation in the case of acyloxy derivatives.     

Metallo-guanines and metallo-guanosines

Metallo-guanines of the type [M(G)₂·2H₂O] [M = Ni^II, Fe^II, Cu^II and UO₂ ^II; G = anionic guanine], [M(G)₂(GH)· H₂O] (M = Co^II and Mn^II; GH = neutral guanine), [Pd(G)₂]·2H₂O and [Zn(G)Cl]₂ have been isolated and characterised. Anionic guanine functions as a bidentate ligand and links through N(3) and N(9). E.p.r. data indicate that the Cu^II complex has a highly distorted octahedral structure. The magnetic susceptibility data suggest that the Co^II and Ni^II complexes possess pseudooctahedral geometry. Neutral guanines are probably unidentate and coordinate either through N(3) or N(9). The isolated guanosine complexes are of the types: [M(Gs)₂·H₂O] [M = Ni^II and Cu^II, Gs = anionic guanosine] [Pd(Gs)₂]·2H₂O and [UO₂(Gs)₂]. I.r. data indicate that guanosine also functions as a bidentate ligand, but coordinates through N(1) and C₂ — NH₂. The electronic absorption spectra of the complexes indicate that guanine is a stronger ligand than guanosine.     

Syntheses of 11-hydroxy and 11-hydroxy-11-methyl-14-methoxy-14-azadispiro[5.1.5.2]pentadec-9-ene-7,15-diones

A facile synthesis, which permits regioselective incorporation of hydroxy and/or methyl substituents at position 11 of 14-methoxy-14-azadispiro[5.1.5.2]pentadec-9-ene-7,15-dione, has been described.     

Role of titanium oxidation states in polymerization activity of Ziegler-Natta catalyst: A density functional study

The role of titanium oxidation states in olefin polymerization activity for Ziegler-Natta (ZN) catalyst has been investigated using density functional calculations at B3LYP/LANL2DZ as well as extended LANL2DZ basis that includes diffuse and polarization functions for C, H and Cl. Using the simple [TiCl₂CH₃]ⁿ (n = +1, 0, −1) model catalyst systems, we could rationalize some of the well-known experimental facts with varying Ti oxidation states (+4, +3, +2) in the real ZN systems. Firstly, irrespective of Ti oxidation states, the activation barriers (E_act) for ethylene and syn propylene insertion in Ti-CH₃ bond are comparable in accordance with experimental and modeling studies. Secondly, it was observed that Ti(IV) catalyst has the lowest E_act which progressively increase in the order Ti(IV) < Ti(III) < Ti(II) high spin < Ti(II) low spin catalysts in line with experimental and several modeling results. The effect of solvation on olefin insertion barriers are seen more prominent in case of Ti(IV) systems compared to other oxidation states.     

Chemistry of 5(2H)-isoxazolones: Novel conversion of positional isomers

Reactions of 4-arylidene-3-methyl-5(4H)-isoxazolones with nucleophiles lead to 4-substituted-benzyl-3-methyl-5(2H)-isoxazolones. Formation of 5(4H)- and 5(2H)-isoxazolone derivatives have been observed when 4-substituted-arylidene-3-rriethyl-5(4H)-isoxazolones are reacted with methyl magnesium iodide. Oxidation of 4-substituted-benzyl-3-methyl-5(2H)-isoxazolones with manganic acetate and pyridinium chlorochromate, gives 4,4′-bis[4-substituted-benzyl-3-methyl-5(4H)-isoxazolone]. Oxidation of 4-substituted-benzyl-3-methyl-5(2H)-isoxazolones with metachloroperbenzoic acid gives 4-hydroxy-4-substituted-benzyl-3-methyl-5(4H)-isoxazolones and reactions of the same substrates with N-bromosuccinimide furnish 4-bromo-4-substitutedbenzyl-3-methyl-5(4H)isoxazolones.