Biotransformation of α-Pinene to Terpineol by Resting Cell Suspension of Absidia corulea.

Microbial biotransformation of monoterpenes results in the formation of many valuable compounds. Many microorganisms can be used to carry out extremely specific conversions using substrates of low commercial value. Absidia corulea MTCC 1335 was examined for its ability to transform α-Pinene enantiomers. The substrates (-)-α-Pinene and (+)-α-Pinene converted to α-terpineol and isoterpineol, were detected in gas chromatographic analysis. The Biotransformation kinetics of the oxidized products were analysed using GC-MS. With both the substrates the products formed were similar and not much difference in the rate of transformation was observed, suggesting no enantioselectivity of organism towards the substrate.

Differentiation of the diastereomeric synthetic precursors of isofebrifugine and febrifugine by electrospray ionization tandem mass spectrometry.

Febrifugine is an alkaloid with potent antimalarial activity isolated from Dichroa febrifuga and Hydrangea umbellate, and it exists naturally with its diastereomeric component, isofebrifugine. Here we report the differentiation of diastereomeric synthetic precursors of isofebrifugine (1, cis) and febrifugine (2, trans) and a structurally similar model diastereomeric pair without a halogen substituent (3 and 4) by electrospray ionization (ESI) tandem mass spectrometry. Compounds 1-4 contain a tert-butoxycarbonyl (BOC) substituent, and the collision-induced dissociation (CID) spectra of the [M+H](+), [M+Na](+) and [M+Li](+) ions of 1-4 include the expected product ions corresponding to the loss of C(4)H(8) (isobutene) and of C(5)H(8)O(2) (BOC-H). Loss of C(5)H(8)O(2) is dominant in cis isomers (1 and 3) and/or loss of C(4)H(8) ions is dominant in trans isomers (2 and 4). The decomposition of [M+H](+) ions shows stereoselectivity in the formation of the [M+H-(BOC-H)-C(3)H(5)OBr](+) and [M+H-(BOC-H)-C(6)H(5)CH(2)OH](+) ions. The [M+Cat](+) ions (where Cat = Na or Li) additionally show loss of NaBr and HBr from [M+Cat-(BOC-H)](+), and these product ions are constantly more abundant in cis isomers than in trans isomers. The stereoselectivity for the product ion corresponding to the loss of [(BOC-H)+C(3)H(5)OBr] from [M+H](+) ions differs from that from [M+Cat](+) ions.

Development of a validated RP-LC/ESI-MS-MS method for separation, identification and determination of related substances of tamsulosin in bulk drugs and formulations.

A reversed-phase high performance liquid chromatographic (RP-HPLC) method for evaluation of purity of tamsulosin in bulk drugs and pharmaceuticals was developed. The separation was accomplished on an Inertsil C(18) column using 10 mM ammonium acetate: acetonitrile as a mobile phase in a gradient elution mode. A photodiode array detector set at 280 nm was used for detection. The impurities were identified by ESI-MS-MS. The detection limits were 0.06-0.11 microg/ml. The method was validated with respect to accuracy, precision, linearity, ruggedness and limits of detection and quantification. It finds application not only for monitoring the reactions during the process development but also on quality assurance of tamsulosin.

Differentiation of diastereomeric N-aryltetrahydropyrano/tetrahydrofuranochromenylamines under electron ionization and chemical ionization conditions.

A series of diastereomeric 4S,5S,6R/S-tetrahydropyrano- and 3S,4S,5R/S-tetrahydrofuranochromenylamine derivatives (a/b isomers; 1-26) has been studied under electron ionization (EI) and chemical ionization (CI) conditions. The EI mass spectra of all diastereomeric compounds show two characteristic fragment ions, of which one is formed by retro-Diels-Alder (RDA) reaction from the molecular ion, retaining the charge on the diene fragment, and the other [M-(HNAr)]+ ion by a simple radical loss. The RDA process is more favorable in all b isomers, whereas the radical loss is dominant in all a isomers; based on these two ions it is easy to differentiate the two diastereomers. The collision-induced dissociation (CID) spectra of all the molecular ions also show the same trend, which reflects the stereoselectivity in the formation of the two characteristic fragment ions. The results of theoretical calculations performed are in accordance with the experimental observations. The CI experiments (methane and isobutane) on all the diastereomeric compounds also enabled the differentiation of the isomers.

Matrix-assisted laser desorption/ionization studies on transition metal complexes of benzimidazole thiosemicarbazones.

The transition metal (M=Fe, Co, Ni, Cu, Zn, Cd and Hg) complexes of 2- acetylbenzimidazolethiosemicarbazone (L(1)) and 1-methyl 2-acetylbenzimidazole-thiosemicarbazone (L(2)) are analyzed by MALDI using HCCA, THP, MMNPD and DMN as the matrices. All the MALDI spectra are clean without any contribution from the complex ions resulted by multiple proton addition/removal. All the complexes, except Cu, irrespective of the matrix used, show 1:2 complex ions wherein two ligands (neutral or deprotonated) complex with the metal ion depending on the nature and stable oxidation state of the central metal ion viz., [M + 2L - 2H](+) ion for Fe and Co complexes (+3 oxidation state) and [M + 2L - H](+) ion for Ni, Zn, Cd and Hg (+2 oxidation state). The Cu complex show 1:1 complex ion corresponding to [2M + 2L - 2H](+) ions. When HCCA is used as a matrix, the complex ions due to ligand exchange by matrix are also found, and this process is relatively more if a neutral ligand is bound to the metal ion in the original complex ion. The type of complex ions found under MALDI experiments are similar to those found under ESI experiments. However, the complex ions due to reduction of Cu are found only in the MALDI analysis of Cu complexes.

Mass spectral studies of meso-dialkyl, alkyl aryl and cycloalkyl calix(4)pyrroles under positive and negative ion electrospray ionization conditions.

A series of meso-dialkyl, alkyl aryl and cycloalkyl calix(4)pyrroles (1-15) are studied under positive and negative ion electrospray ionization (ESI) conditions. The positive ion spectra show abundant [M + H](+) and [M + Na](+) ions and the negative ion spectra show the [M + Cl](-) (the Cl(-) ions from the solvent) and [M - H](-) ions. The collision induced dissociation (CID) spectra of [M + H](+), [M + Na](+), [M + Cl](-) and [M - H](-) ions are studied to understand their dissociation pathway and compared to that reported for M(+) under electron ionization (EI) conditions. The beta-cleavage process that was diagnostic to M(+) is absent in all the CID spectra of the ions studied under ESI. Dissociation of all the studied ions resulted in the fragment ions formed by sequential elimination of pyrrole (A) and/or dialkyl/alkyl aryl/cycloalkyl (B) groups involving hydrogen migration to pyrrole ring at each cleavage of A--B bond, which clearly reveals the arrangement of A and B groups in the calix(4)pyrroles. The source of hydrogen that migrates to pyrrole ring during A--B bond cleavage is investigated by the experiments on deuterated compounds and [M + D](+) ions; and confirmed that the hydrogen attached to pyrrole nitrogen, hydrogen on alpha-carbon of alkyl group and the H(+)/Na(+) ion that added during ESI process to generate [M + H](+)/[M + Na](+) ions involve in the migration. The yields of [M + Na](+) ions are found to be different for the isomeric meso-cycloalkyl compounds (cycloheptyl, and 2-, 3- and 4-methyl cyclohexyl) and for normal and N-confused calix(4)pyrroles. The isomeric methyl and 3-hydroxy/4-hydroxy phenyl calix(4)pyrroles show specific fragmentation pattern during the dissociation of their [M - H](-) ions.

Differentiation of diastereomeric conduramine derivatives under electron ionization and chemical ionization mass spectral conditions.

Diastereomeric conduramine derivatives, i.e., (1R,2S,3R/S,6S)-6-(N-carbomethoxyamino) 1,2-O-isopropylidenecyclohex-4-ene-1,2,3-triol (1 and 2) and their O-acetyl derivatives (3 and 4), were studied using gas chromatography (GC) with electron ionization (EI) and chemical ionization (CI). The EI mass spectra of diastereomeric pairs show consistent differences in the relative abundances of characteristic ions. The EI fragmentation patterns are based on precursor/product ion spectra, high-resolution mass spectrometry (HRMS) and deuterium labelling. The CI spectra show differences from the EI spectra, and the isobutane/CI spectra are much simpler than the methane/CI spectra. The differences shown in the CI spectra are similar to those shown in the product ion spectra of [M+H](+) ions generated under electrospray ionization (ESI) conditions. Theoretical calculations are performed to understand the observed differences. The differences in the relative stabilities of molecular ions, or protonated molecules at different sites, can explain the observed differences in the spectra.

Differentiation of isomeric substituted diaryl ethers by electron ionization and chemical ionization mass spectrometry.

A series of isomeric substituted diaryl ethers, i.e., 2- or 4-NO2, 5- FC6H3OC6H4 (4-R), where R=H, COCH3, COOCH3, NO2, CHO, OCH3 etc., which comprise ortho and para isomers with respect to the position of the nitro group are studied under GC-EI-MS and CI-MS conditions. The EI mass spectra of ortho and para isomers show distinct fragment ions, where the [MOH]+ and [MOHO]+ ions specifically appeared in all spectra of the ortho isomers (I), whereas the para isomers (II) contain [MO]+ and [MNO]+ ions. The [MOHCO]+ and [MOHNO]+ ions in I, and [MNO2]+ ion in II are the other specific fragment ions observed but feasibility of these fragment ions are found to depend on the nature of the substituent (R). The substitution (R) effect is also clearly reflected in the formation of fragment ions due to sigma-cleavage process with or without hydrogen migration. Similar differences in the formation of specific fragment ions are also observed in ortho and para isomers of substituted aryl naphthyl ethers. The methane/CI of isomeric compounds resulted in the same set of fragment ions, but prominent differences are observed in the relative abundance of [MHNO]+, which is relatively higher in para isomers compared with corresponding ortho isomer.