Masaatsu Adachi

Combinatorial synthesis of trisaccharides via solution-phase one-pot glycosylation

Abstract A library of 72 trisaccharides constructed from a combination of glucosides, galactosides, and mannosides via solution-phase one-pot glycosylation was synthesized rapidly using a manual synthesizer.

Synthesis of di-branched heptasaccharide by one-pot glycosylation using seven independent building blocks.

[reaction: see text] We describe an efficient synthesis of di-branched heptasaccharide 1 having phytoalexin elicitor activity in soybeans by one-pot glycosylation. The synthesis involves chemo- and regioselective sequential six-step glycosylations using seven independent building blocks and sequential removal of acyl- and benzyl ether-type protecting groups. The coupling of seven building blocks requires only four chemoselective activitable leaving groups of glycosyl donors. Both the glycosylation and deprotection reactions can be achieved utilizing a parallel manual synthesizer.

First Identification of 5,11-Dideoxytetrodotoxin in Marine Animals, and Characterization of Major Fragment Ions of Tetrodotoxin and Its Analogs by High Resolution ESI-MS/MS

Even though tetrodotoxin (TTX) is a widespread toxin in marine and terrestrial organisms, very little is known about the biosynthetic pathway used to produce it. By describing chemical structures of natural analogs of TTX, we can start to identify some of the precursors that might be important for TTX biosynthesis. In the present study, an analog of TTX, 5,11-dideoxyTTX, was identified for the first time in natural sources, the ovary of the pufferfish and the pharynx of a flatworm (planocerid sp. 1), by comparison with totally synthesized (−)-5,11-dideoxyTTX, using high resolution ESI-LC-MS. Based on the presence of 5,11-dideoxyTTX together with a series of known deoxy analogs, 5,6,11-trideoxyTTX, 6,11-dideoxyTTX, 11-deoxyTTX, and 5-deoxyTTX, in these animals, we predicted two routes of stepwise oxidation pathways in the late stages of biosynthesis of TTX. Furthermore, high resolution masses of the major fragment ions of TTX, 6,11-dideoxyTTX, and 5,6,11-trideoxyTTX were also measured, and their molecular formulas and structures were predicted to compare them with each other. Although both TTX and 5,6,11-trideoxyTTX give major fragment ions that are very close, m/z 162.0660 and 162.1020, respectively, they are distinguishable and predicted to be different molecular formulas. These data will be useful for identification of TTXs using high resolution LC-MS/MS.

Streptomyces phospholipase D mutants with altered substrate specificity capable of phosphatidylinositol synthesis.

The substrate specificity of a phospholipase D (PLD) from Streptomyces antibioticus was altered by site‐directed saturation mutagenesis, so that it was able to synthesize phosphatidylinositol (PI). Mutations were introduced in the pld gene at the positions corresponding to three amino acid residues that might be involved in substrate recognition, and the mutated genes were expressed in Escherichia coli BL21 (DE3). High‐throughput screening of approximately 10 000 colonies for PI‐synthesizing activity identified 25 PI‐synthesizing mutant PLDs. One of these mutant enzymes was chosen for further analysis. The structure of the PI synthesized with the mutant enzyme was analyzed by HPLC‐MS and NMR. It was found that the mutant enzyme generated a mixture of structural isomers of PIs with the phosphatidyl groups connected at different positions of the inositol ring. The phosphatidylcholine‐hydrolyzing activity of the mutant PLD was much lower than that of the wild‐type enzyme. The mutant enzyme was able to transphosphatidylate various cyclohexanols with a preference for bulkier compounds. This is the first example of alteration of the substrate specificity of PLD and of PI synthesis by Streptomyces PLD.

An Improved Synthesis of (−)-5,11-Dideoxytetrodotoxin

We describe an improved synthesis of (-)-5,11-dideoxytetrodotoxin from an enone, which was used for synthesis of tetrodotoxin and its analogues in this laboratory. One of the major modifications was to establish a two-step guanidinylation of trichloroacetamide of a highly functionalized intermediate, which allowed us to prepare (15)N(2)-labeled 5,11-dideoxytetrodotoxin for biosynthetic investigations.

Total Synthesis of Chiriquitoxin, an Analogue of Tetrodotoxin Isolated from the Skin of a Dart Frog

The first total synthesis of chiriquitoxin, the most structurally complex analogue of tetrodotoxin isolated from a Costa Rican dart frog, has been accomplished from a newly designed intermediate for a variety of tetrodotoxin derivatives. The synthesis includes the third total synthesis of tetrodotoxin in this laboratory, and its intermediate was transformed into chiriquitoxin by a stereocontrolled aldol reaction with a D-camphor-derived lactone for installation of the unique side chain, and a new deprotection of methylthiomethyl (MTM) ether by using a Pummerer rearrangement.

Synthesis of 5- and 8-deoxytetrodotoxin.

Tetrodotoxin, a toxic principle of puffer fish intoxication, is one of the most famous marine natural products owing to its complex structure and potent biological activity, which leads to fatal poisoning. Continuous synthetic studies on tetrodotoxin and its analogues to elucidate biologically interesting issues associated with tetrodotoxin have led to the development of versatile routes for a variety of tetrodotoxin derivatives. With the aim of investigating the structure-activity relationship of tetrodotoxin with voltage-gated sodium channels, this study describes the first total syntheses of 5-deoxytetrodotoxin, a natural analogue of tetrodotoxin, and 8-deoxytetrodotoxin, an unnatural analogue, from a newly designed, versatile intermediate in an efficient manner. An estimation of the biological activities of these compounds reveals the importance of the hydroxy groups at the C-5 and C-8 positions on the inhibition of voltage-gated sodium channels.

Stereocontrolled synthesis of an indole moiety of sespendole and stereochemical assignment of the side chain.

Two possible diastereomers of the indole moiety of sespendole were synthesized from 3-hydroxy-4-nitrobenzaldehyde in a highly stereoselective manner. Comparison of (1)H and (13)C NMR spectra of the two synthetic materials with those sespendole leads us to propose that the relative stereochemistry of the epoxyalcohol is syn.

A New Ring Expansion for a Chiral Hexahydroazulene Skeleton Possessing an Angular Methyl Group

A new synthetic route for a pseudoguaiane ring system is described. The synthesis features an Ireland-Claisen rearrangement for constructing the trans-fused ring system, followed by a new ring expansion to yield a bicyclo[5.3.0]decane ring system possessing an angular methyl group.

Differential binding of tetrodotoxin and its derivatives to voltage‐sensitive sodium channel subtypes (Nav1.1 to Nav1.7)

The development of subtype‐selective ligands to inhibit voltage‐sensitive sodium channels (VSSCs) has been attempted with the aim of developing therapeutic compounds. Tetrodotoxin (TTX) is a toxin from pufferfish that strongly inhibits VSSCs. Many TTX analogues have been identified from marine and terrestrial sources, although their specificity for particular VSSC subtypes has not been investigated. Herein, we describe the binding of 11 TTX analogues to human VSSC subtypes Nav1.1–Nav1.7.