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Mechanisms of fragmentation of giycosyl bond linkages in various saccharides were investigated by using computational calculations to find general rules of fragmentation of sodiated oligosaccharides in mass spectrometry. The calculations revealed that [alpha]-Glc, [alpha]-Gal, [beta]-Man, [alpha]-Fuc, [beta]-GlcNAc, and [beta]-GalNAc linkages were cleaved more easily than [beta]-Glc, [beta]-Gal, and roman linkages because the transition states of the former were stabilized by the anomeric effect. The 1-6 linkage was more stable than the others, since saccharides with flexible 1-6 linkages were more stabilized in energy than the other linkages by the sodium cation. The sialyl linkage was the most labile of all the linkages investigated. Comparison of activation energies and binding affinities to the sodium cation revealed an increase in activation energy in proportion to the increment in binding affinity. The calculated stabilities of glycosyl bonds were: [alpha]-Man (Man[alpha] 1-3 Man, Man[alpha] 1-4Man, Man[alpha]l-6Man) > [beta]-Gal (Gal[beta]1-4Gal) > [alpha]-GalNAc (GalNAc[alpha]1-4GalNAc) > t-Man (Man[beta]ll-4GlcNAc) > [alpha]-Gal (Galc[alpha]1-3Gal, Gal[alpha]1-4Gal, Galc[alpha]l-6Gal) > [beta]-Man(Man[beta]l-4Man) > [beta]-GalNAc (GalNAc[beta]l-4GalNAc) > [alpha]-Fuc (Fuc[alpha]l-6GlcNAc) > [alpha]-Fuc (Fuc[alpha]1-4GlcNAc) > [beta]-GlcNAc (GlcNAc[beta]l-4GlcNAc) > [alpha]-Fuc (Fuc[alpha]1-3GlcNAc) > [alpha]-NeuNAc (NeuNAc[alpha]2-3Gal, NeuNAc[alpha]2-6Gal); this result was close to the experimentally deduced trend. These theoretically and experimentally derived general rules for fragmentation should be useful for analyzing the experimentally obtained mass spectra of oligosaccharides.

The configuration isomers [alpha], [alpha]-, [alpha], [beta]-, and [beta], [beta]-trehalose are distinguishable by a relative ion abundance analysis using collision-induced dissociation MS/MS measurements in electrospray ionization quadrupole-time-of-flight mass spectrometry. The relative abundance of the Y-type fragment ion of [alpha], [alpha]-trehalose is the highest and that of [beta], [beta]-trehalose is the lowest, indicating that [alpha]-glycosyl bonds cleave more easily than [beta]-glycosyl bonds. The relative ion abundance depends on both the [alpha]- and [beta]-glycosyl linkage type and the number of [alpha]-glycosyl bonds. The reaction path of glycosyl bond cleavage is calculated computationally using the molecular orbital method in the form of Hartree-Fock theory in conjunction with the 6-31G(d) basis set. The results are consistent with the experimental data. Isotope effects on the fragmentation of the glycosyl bonds are detected in the experiments of the [H.sub.2]O/[D.sub.2]O solvent systems. Furthermore, the isotope effect regarding [beta], [beta]-trehalose is larger than those of [beta], [beta]- and [alpha], [beta]-trehalose, indicating that the isotope effect on the [beta]-glycosyl bond cleavage is larger than that on the [alpha]-glycosyl bond cleavage. The thermal energy increase in trehalose-[d.sub.8] molecules over the corresponding trehalose molecules is calculated from the vibrational modes.

When the mass spectra of biological samples (proteins, peptides, and so on) are obtained routinely by matrix-assisted laser desorption/ionization mass spectrometry (MALDI-MS), a serious problem is the reduction of the ionization efficiency by impurities, such as buffer salts and detergents. We focused our attention on devising a method to maintain the ionization efficiency of protein samples, even in the presence of sodium dodecyl sulfate (SDS), without any extra purification step. Although no protein ion peaks are observed in the presence of 2.5% SDS with the usual methods, the addition of a granular anion exchange silica gel to the matrix solution allowed the protein ion peaks to be obtained with an excellent signal-to-noise ratio. Together with other supporting experiments, we suggest that the positively charged surface (the basic environment derived from the anion exchange groups) and the roughness of the particles were important for good ionization in the presence of a high SDS concentration. For a very uneven surface, the SDS might be absorbed into the particle interiors during the process of cocrystallization with the matrix and analytes, which is known as the molecular sieve effect, and the SDS concentration in the surface crystalline film might be reduced. As a result, we developed an on-probe sample preparation method without washes for MALDI, using a strong anion exchange silica gel. This method is applicable even in the presence of 2.5% SDS, and is not only very simple but also inexpensive, because it can be used with the standard MALDI target plates.

Cross-ring cleavage ions produced by in-source decay (ISD), as well as deprotonated molecular ions [M - H]-, are invariably observed in negative-ion linear-mode matrix-assisted laser desorption/ionization time-of-flight mass spectrometry spectra of neutral oligosaccharides with 9H-pyrido [3,4-blindole (norharman) as a matrix. The patterns of ISD ions depend on the oligosaccharide linkage type; thus, these ions are potentially useful in linkage analysis. In postsource decay (PSD) spectra from chlorinated molecular ions [[M + CI].sub.-], all PSD ions are observed in the deprotonated form, although no deprotonated molecular ions are detected. In oligosaccharides having an alditol at the reducing end, deprotonated molecular ions [[M - H].sup.-] are clearly seen in linear-mode mass spectra and survive in the PSD measurements. These results indicate that the deprotonation process drives ISD and PSD of oligosaccharides and that keto-enol tautomerization at the reducing terminal promotes ISD and PSD processes.

The description of the first total synthesis of (-)-gambierol, a marine polycyclic ether toxin, is presented. A convergent union of the ABC and EFGH ring fragments is one of the key features of this synthesis.

Research has been conducted on the ciguatoxin's (E)FGN ring system. The convergent synthetic route to this system has been developed and the results indicate that the synthesis involves convergent coupling used in producing dioxane acetal and the ring-closing metathesis used in producing hexahydrooxonine ring F.

A convergent synthesis of the decacyclic ciguatoxin model has been carried out. Results indicate that it has been achieved through the pentacyclic oxonane assembly.

Research has been conducted on the ciguatoxin JKLM ring fragment. A stereocontrolled synthesis of this ring fragment is discussed.

A study was conducted to investigate the stereochemistry of lipogrammistin-A, a lipophilic ichthyotoxin of the marine fish, soapfish, by chemical degradation and by the total synthesis of possible diastereomers. The C4 position stereochemistry was determined to be S by a total snthesis of the diastereomers. Results showed that tertiary amides support conformational alteration in solution resulting from the restricted rotation of their amide bonds.

Collision-induced dissociation tandem mass spectrometry was successfully applied to the elucidation of the 18O-incorporation pattern of okadaic acid. The complete assignment of the labeled positions with accurate isotope ratios was afforded by the extensive determination of 18O/16O ratios for each product ion bearing differing numbers of incorporated 18O atoms. This underscores the utility of mass spectrometry methods for the comprehensive analysis of isotope-labeled positions in natural products.

The stereoselective synthesis of ciguatoxin's KLM ring fragment involves 7-endo selective epoxy alcohol cyclization. The cyclization efficiently yields a fully substituted oxepane ring. NOE spectra and model studies enable the assignment of stereochemistry at specific fragment positions.

The isolation and characterization of primary sequence of two okadaic acid binding proteins (OABP1 and OABP2) from marine sponge Halichondria okadai is presented. The results from electrospray ionization mass spectroscopy revealed that OABP2.1 and OABP2.2 form a complex with okadaic acid.