Biomedical subjects
Publications and source records attributed to Hideyo Takahashi.
A poly(N-isopropylacrylamide) (PNIPAAm) gel cross-linked with quaternized aminoalkyls was designed. A novel recyclable system based on the external solvent-responsive oil-absorption/elution transition ability of the PNIPAAm gel matrix was then developed.
An efficient divergent synthesis of L-sugars and L-iminosugars from D-sugars is described. The important intermediate, delta-hydroxyalkoxamate, prepared from D-glucono-/galactono-1,5-lactone, was cyclized under Mitsunobu conditions to give the O-cyclized oxime compound and the N-cyclized lactam compound as mixtures. A more detailed investigation revealed that the appropriate protecting groups and solvents controlled the specificity for the O-/N-cyclization of the delta-hydroxyalkoxamate. Suitable protection at the 6-position of delta-hydroxyalkoxamate, derived from D-glucono-1,5-lactone, afforded the corresponding O-alkylation product alone. Thus we succeeded in applying this to the total synthesis of L-iduronic acid. In contrast, with both TBDMS as the protecting group and RCN as the solvent the efficient conversion of D-glucono/galactono-1,5-lactone into the corresponding L-iminosugars (L-idonolactam and L-altronolactam) was achieved.
9-cis-Retinoic acid (RA) analogues devised to lock the 9-cis double bond by ring formation were synthesized using two stereoselective carbon-carbon bond formation reactions as key steps. The palladium-mediated Suzuki reaction was adopted to construct a 7E-double bond (RA numbering) and the Horner-Emmons olefination was employed for stereoselective 11E-double bond (RA numbering) formation. The synthesized 9-cis-RA analogues that are locked by five-membered ring systems (cyclopentene, dihydrofuran, and dihydrothiophene) were shown to have comparable thrombomodulin induction activities to that of 9-cis RA. Conformational analysis of these compounds showed their similarity to 9-cis RA in the spatial orientation of the side chain and the terminal carboxy group.
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We have found that N-acetylneuraminic acid (NANA) consumes toxic hydrogen peroxide (H(2)O(2)) under physiological conditions. Close investigation of this finding revealed that NANA was oxidized by an equimolar amount of H(2)O(2) to provide its decarboxylated product, 4-(acetylamino)-2,4-dideoxy-D-glycero-D-galacto-octonic acid (ADOA). To date, there have been little data on this reaction, and its physiological significance has not been discussed. Examining the detoxification of H(2)O(2) in cultured cells with NANA, we were able to confirm that the cell death caused by H(2)O(2) was suppressed by NANA in a dose-dependent manner. These results revealed a novel role for NANA as a reactive oxygen scavenger. It is known that terminal NANA residues are removed by neuraminidase and that free NANA molecules are recycled or degraded by enzymes. We propose that released monomeric NANA is the potent defense molecule against oxidative damage.
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An assembled insoluble catalyst, PdAS, prepared from palladium ((NH4)2PdCl4 (1)) and non-cross-linked amphiphilic copolymer poly(N-isopropylacrylamide-co-4-diphenylstyrylphosphine) (2) was developed. It was found that PdAS is an excellent catalyst for the Suzuki-Miyaura reaction on three points: (1) The use of 8 x 10(-7) to 5 x 10(-4) mol equiv of PdAS afforded the coupling products efficiently after easy workup, with the turnover number reaching up to 1,250,000. (2) The catalyst was reusable many times without loss of catalytic activity. (3) PdAS showed good stability in any reaction medium (i.e., water or aqueous or anhydrous organic solvents). Analytical study of PdAS indicates that the phosphines in 2 coordinate to palladium to form PdCl2(PPh2Ar)2 species.
From 2001 to the summer of 2002, more than 800 cases of liver damage were reported in Japan among people taking Chinese diet aids. The Japanese Ministry of Health, Labor and Welfare has recently announced that N-nitrosofenfluramine was the hepatotoxic compound contained in the diet aids based on animal experiments performed by the National Institute of Health Sciences. Although N-nitrosofenfluramine is a derivative of fenfluramine, a previously used antiobesity drug, neither pharmacologic nor toxicologic properties have been reported for N-nitroso fenfluramine. It should be noted that N-nitrosofenfluramine has two optical isomers, although it is not yet known which isomer damages the liver and other organs. The Japanese Ministry of Health, Labor and Welfare has not commented on this point. Pursuing this question, 10 types of Chinese slimming aid samples including those obtained from patients with fulminating hepatitis were analyzed by NMR, GC/MS, and a newly established HPLC method using a chiral separation column. It was found that the N-nitrosofenfluramine in all of the toxic diet aids was the (S)-isomer form. No (R)-isomer was detected. These results strongly suggest that the nitroso-compound in the diets must be prepared from pharmacologically active (S)-fenfluramine (dexfenfluramine). Thus the pharmacologic and toxicologic properties of each isomer should be investigated.
An insoluble and assembled catalyst of palladium and a non-cross-linked amphiphilic polymer were developed. In the presence of 50-500 ppm mol equiv of catalyst, the Suzuki-Miyaura reaction proceeded efficiently under organic solvent-free conditions. The catalyst was reused 10 times without any decrease in activity and was recycled without any special treatment.[structure: see text]
[reaction: see text] D-Mannono-1,4-lactone was efficiently converted into L-ribose in eight steps. A key step of this synthesis is the cyclization of a gamma-hydroxyalkoxamate under Mitsunobu conditions. It is noteworthy that the O-alkylation product was obtained in 94% yield and that none of the N-alkylation product was detected in this cyclization.
The development of two novel ring conversions of sugar derivatives is described. The first is an efficient conversion of 5-enopyranosides and 6-O-acetyl-5-enopyranosides to the corresponding substituted cyclohexanones mediated by a catalytic amount of palladium dichloride. After a survey of various substrates, the reaction was confirmed to be general and useful. Syntheses of bioactive compounds utilizing this method were therefore investigated. Cyclophellitol, which is a potent beta-glucoidase inhibitor, and its diastereoisomer were efficiently synthesized. Furthermore, novel synthesis of all enantiomerically pure diastereoisomers of inositol starting with 6-O-acetyl-5-enopyranosides was investigated. Good accessibility of these enantiomerically pure inositol diastereoisomers results in the efficient syntheses of D-myo-inositol 1,4,5-trisphosphate and D-myo-inositol 1,3,4,5-tetrakisphosphate. The second investigation involved novel and efficient conversion of D-glycono-1,5-lactones into the corresponding L-sugars. The important intermediate, delta-hydroxyalkoxamate, was provided by a practical alkoxyamination of D-glycono-1,5-lactones mediated by Me3Al. In contrast to the preparation of beta-lactam skeletons from beta-hydroxyalkoxamates, the cyclization of delta-hydroxyalkoxamates under Mitsunobu conditions resulted in O-alkylation rather than N-alkylation. It is noteworthy that delta-hydroxyalkoxamates derived from D-mannono-1,5-lactones afforded the O-alkylation product in 91% yield. No N-alkylation product was detected in this case. These O-cyclized oximes, in which the inversion of the configuration at C5 was secured, were efficiently converted into L-sugars.