Noboru Yamamoto

Synthesis of a common key intermediate for (−)-tetrodotoxin and its analogs

Abstract A key intermediate for tetrodotoxin and its analogs such as (−)-5,11-dideoxytetrodotoxin was stereoselectively synthesized from a chiral starting material, levoglucosenone, via Diels–Alder reaction and the Overman rearrangement as key steps. The Overman rearrangement of the precursor bearing hydroxy group of C-8 was also described.

Stereocontrolled Synthesis of (−)‐5,11‐Dideoxytetrodotoxin

New derivatives of an intriguing marine natural product are now accessible. The first asymmetric synthesis of the simple tetrodotoxin analogue, 5,11-dideoxytetrodotoxin (3), was achieved. Hydroxylation at position C8 of the key intermediate 1 relied on the neighboring trichloroacetamide group, and stereoselective elaboration of the vinyl group gave alpha-hydroxylactone 2, which was transformed into the title compound through a new guanidylation method.

Stereocontrolled synthesis of (−)-5,11-dideoxytetrodotoxin

New derivatives of an intriguing marine natural product are now accessible. The first asymmetric synthesis of the simple tetrodotoxin analogue, 5,11-dideoxytetrodotoxin (3), was achieved. Hydroxylation at position C8 of the key intermediate 1 relied on the neighboring trichloroacetamide group, and stereoselective elaboration of the vinyl group gave alpha-hydroxylactone 2, which was transformed into the title compound through a new guanidylation method.

New synthetic route of guanidine from trichloroacetamide for tetrodotoxin and its related compounds

Abstract Trichloroacetamide was transformed into dibenzylguanidinium salt in three steps. Attempted debenzylation was very difficult in the guanidinium form even under high pressure hydrogen and high temperature conditions. On the other hand, the benzyl groups on acetylated guanidine were easily deprotected by hydrogenolysis under 1 atm of hydrogen. These methods were applied to the syntheses of tetrodotoxin-related compounds.

Chemoselective introduction of acetylene into hindered carbonyl group using alkynyltrifluoroborate, a solution as one step to (−)-tetrodotoxin

Abstract Optically active cyclohexane moiety precursor for tetrodotoxin molecule was synthesized by Diels-Alder cycloaddition between a bromo derivative of levoglucosenone and Danishefsky type diene. The unstable product, bromo-ketone, was converted into vinylphosphinate and then the carbonyl compounds, to which the critical carbon nucleophile was predominantly introduced with alkynyltrifluroborate. The Lewis acid played an important role for switching the selectivity toward the carbonyl carbon or phosphorous atom.

Studies on Zeolite Catalysts Part 1

In our previous work, it was found that Ce cation-exchanged and platinum loaded zeolite catalysts had low activities for n-pentane isomerization when the catalysts were dehydrated by high temperature hydrogen treatment, and their activities were considerably improved by charging n-pentane with small amounts of isopropyl alcohol. In the present work, the influence of hydrogen treating temperature and the effect of steam treatment on the catalytic activities were studied in regards to La, Nd, or Ce cation-exchanged catalyst.The higher the hydrogen treating temperature were, the lower the activities were for n-pentane isomerization. The activities of the catalysts were improved by steam treatment and showed almost equal activity level regardless of prior hydrogen treating temperature.These results support our previous suggestion that the active sites of the catalysts are formed by adsorption of water on the catalyst surface. It is further concluded that the water is easily chemisorbed or desorbed without substantial collapse of the crystal structure by an adequate treatment.

Studies on Activities of Industrial Moving Bed Cracking Catalyst

Aging characteristics of synthetic silica-alumina catalyst and kaolin-clay catalysts were studied for fresh and equilibrated catalyst, using light gas oil as a feed stock. Fresh synthetic silica-alumina catalyst is superior in cracking activities than kaolin-clay catalyst, but as an equilibrated catalyst, both have almost the same cracking properties except that the selectivity of synthetic silica-alumina catalyst is slightly higher.Cracking activities of the two catalyst could not be estimated as being related from the measurements of the surface areas and acidities by Holms method, however, it seems that acidities of the catalyst measured by the Benesis method have some correlation with cracking activities. Cracking activities of the above catalysts under different feed stocks were studied for comparison. When light gas oil was used as a feed stock synthetic silica-alumina catalyst showed much better activity than kaolin-clay catalyst. However, as the boiling range of the feed stocks increased the difference in activities became smaller, especially when the feed stock contained much polycyclic aromatics.