Hiroko Kasai

Separation of stereoisomers of several furan derivatives by capillary gas chromatography-mass spectrometry, supercritical fluid chromatography, and liquid chromatography using chiral stationary phases.

The direct separation of several stereoisomers (enantiomers and geometrical isomers) of furan derivatives, important intermediates for the synthesis of physiologically active natural products, was achieved using capillary gas chromatography/mass spectrometry with a per-O-methyl-beta-cyclodextrin, supercritical fluid chromatography and high-performance liquid chromatography with a tris(3,5-dimethylphenylcarbamate) of cellulose or amylose for the chiral stational phases, respectively. The temperature dependence of the peak resolution (Rs) and the retention factor (k) over the range of 110-130 degrees was studied using crotyl furfuryl ether in gas chromatography. Successive increases in the Rs value and of the difference between the k value of the E-isomer and the k value of the Z-isomer were observed when the gradient temperature was decreased. The per-O-methyl-beta-cyclodextrin column was suitable for use with volatile furan ethers whose molecular masses are between 150 and 180. In conclusion, the separation of thermally unstable furan derivatives was accomplished using supercritical fluid chromatography and high-performance liquid chromatography.

HIGH-PERFORMANCE LIQUID CHROMATOGRAPHY-TANDEM MASS SPECTROMETRY OF CARDIAC STEROIDS

High performance liquid chromatography-tandem mass spectrometry (LS/MSn) utilizing an ion trap mass spectrometer has been used for the analyses of representative cardiac steroids. In the case of bufotoxin having a polar residue (suberoylarginine), the positive-electrospray ionization (ESI) was 50 times more sensitive than the atmospheric pressure chemical ionization (APCI) and provided information concerning the molecular weight as well as the structures of both aglycone and suberoylarginine. The corresponding bufogenin showed 2 times better sensitivity in the positive-APCI than ESI. The mass spectrum of digoxin with the positive-APCI showed fragment ions not only derived from aglycone but also formed by losses of sugars. The cleavage of the dioxane ring has been observed on the cardiac glycoside having an unusual sugar linkage. Fast atom bombardment mass spectra of these compounds were examined and compared with the data obtained from LC/MSn.

Structural features of polyacylated anthocyanins using matrix‐assisted laser desorption/ionization and electrospray ionization time‐of‐flight mass spectrometry

In our continuing studies to isolate water-soluble vacuolar pigments, we expect to elucidate more structural details using mass spectrometry (MS). Because of its sensitivity, only a small amount of pigment extracted from natural plants is required for MS measurement. Nuclear magnetic resonance is also a useful spectroscopic method for structural determination. In this study, two soft ionization techniques, electrospray ionization (ESI) and matrix-assisted laser desorption/ionization (MALDI), on time-of-flight (TOF) mass spectrometers, were used to analyze five polyacylated anthocyanins with more than two aromatic acid molecules in the side chains. ESI is advantageous for the detection of individual molecular ions, while MALDI is essential for the detection of characteristic fragment ions originating from the anthocyanidin. Although 2,5-dihydroxybenzoic acid (DHBA) is an effective matrix in MALDI-TOFMS to obtain informative fragment ions of polyacylated anthocyanins, α-cyano-4-hydroxycinnamic acid (CHCA) is the preferred matrix for the identification of aglycones. In particular, in measurements of polyacylated anthocyanins with two acylated glycoside chains, fragment ions originating from anthocyanidin can only be observed in MALDI-TOFMS using CHCA as the matrix.

Investigation of 5-(3-Trifluoromethylbenzylidene)thiazolidine-2,4-dione as a Matrix for Analyses of Biogenic Monoamine Transmitters Using MALDI-MS.

In order to discover new matrices suitable for the analyses of low molecular-weight compounds using positive-ion mode matrix-assisted laser desorption/ionization (MALDI) time-of-flight mass spectrometry (MS), 5-(3-trifluoromethylbenzylidene)thiazolidine-2,4-dione (3-CF3-BTD) was synthesized, and its effectiveness was compared with that when commercially available α-cyano-4-hydroxycinnamic acid was used. 3-CF3-BTD was sufficiently sensitive to analyze neurotransmitters, i.e., dopamine, serotonin, histamine, and epinephrine, in amounts of several picomoles. Similar to vacuum MALDI experiments, atmospheric-pressure MALDI-MS measurements using 3-CF3-BTD as a matrix also detected dopamine.

Synthetic approach to natural products by Claisen rearrangement of glyceraldehyde derivatives

For the purpose of organic syntheses of some corynanthe-type indole alkaloids, sesquiterpenes, and steroids, optically active intermediates cyclopentanone 3-allylalcohol, α-methylene-γ-butylo lactones andtrans-hydrindanone-propionic acid, were synthesized from (R)- and (S)-isopropylideneglyceraldehyde derived fromD-mannitol andLascorbic acid, respectively, utilizing Claisen rearrangement as a key reaction. Actually total syntheses of natural alkaloids, (-)-antirhine, (+)-dihydroantirhine and (-) dihydrocorynantheol were accomplished.