Namiko Toh

Circular dichroism of hydrolysable tannins-I ellagitannins and gallotannins

Abstract The Cotton effects around 235, 265 and 285 nm in the CD spectra of twenty hydrolysable tannins and related compounds were empirically correlated with the stereostructures of ellagitannins and gallotannins.

Guest-induced conformational change of β-cyclodextrin capped with an environmentally sensitive chromophore

Abstract A capped cyclodextrin, 6-deoxy-6-( p -hydroxy- m -nitrophenacylthio)-β-cyclodextrin, was prepared in order to detect any conformational change of the host upon the guest binding. The association constant between the cyclodextrin and 1-adamantanecarboxylate, cyclohexanecarboxylate, p -methylbenzoate, 3,3-dimethylbutyrate, or 2,2-dimethylpropionate was enhanced 20, 5.3, 3.7, 2.3, or 2.0 times, respectively, by chromophore capping. The changes in the electronic, NMR, and circular dichroism spectra as well as p K a of this cyclodextrin upon binding of the guest strongly indicate a conformational change around the chromophoric moiety of the cyclodextrin.

New diterpene esters from Aleurites fordii fruits

Abstract A toxic diterpenoid diester and a monoester were isolated from the fruits of Aleurites fordii . The structure of the monoester was found to be 13- O -acetyl-16-hydroxyphorbol by transforming it into bisdehydrophorbol-(12,20)-diacetate. The structure of the toxic constituent was established as 12- O -palmityl-13- O -acetyl-16-hydroxyphorbol by partial synthesis from the monoester.

Circular dichroism of hydrolysable tannins-II dehydroellagitannins

Abstract The CD spectra of dehydroellagitannins and related compounds have empirically shown that the absolute configuration at C-1′ of the dehydrohexahydroxydiphenoyl group can be determined by the Cotton effect around 200 nm.

Selective recognition of alkanoates by a β-cyclodextrin flexibly capped with a chromophore

Abstract The association between 6-deoxy-6-( p -hydroxy- m -nitrophenacylthio)-β-cyclodextrin 1 and sodium n -alkanoate, sodium 2,2-dimethylpropionate, or sodium 3,3-dimethylbutyrate was investigated. Host-guest association was measured by means of electronic spectroscopy and circular dichroism spectroscopy and ascertained to be 1:1. The inclusion of 2,2-dimethylpropionate or butanoate marginally affected the circular dichroism spectrum of 1. The inclusion of 3,3-dimethylbutyrate, hexanoate, octanoate, decanoate, or dodecanoate, however, dramatically affected the spectrum of 1. The plots of molecular ellipticities of the inclusion complexes against the carbon number of the n -alkanoates were sigmoid. From these observations, the effective size of the guest molecule to push the chromophore in the cavity to the capping position was estimated. From the similarity of the spectrum of the octanoate- 1 complex to that of 1-adamantanecarboxylate- 1 complex, the carbon chain of octanoate appears to be folded in the cavity of the cyclodextrin.

A Mild And Efficient Synthesis of Diamino-Steroids

Abstract α γ-Dibromo-α β-enones readily react with various secondary cyclic amines at ambient temperature to afford the corresponding α γ-diamino-enones in high yields.

Reaction of α-Halo-Enones with Heterocyclic Bases. A Mild and Efficient Synthesis of Amino-Steroids

Abstract A number of steroids containing cyclic amino functions have been prepared and studied for biological activities, and some of them have proved to be clinically useful as a neuromuscular blocking agent, an antitumour agent, and so on.1 As the conventional methods, the reactions of cyclic amines with halides2 or epoxides,3 the reductive amination of ketones,4 and the reduction of enamines5 have been widely used for introducing these amino functions into steroid nucleus.