Tadamitsu Sakurai

Complexation and proton dissociation behavior of 7-hydroxy-4-methylcoumarin and related compounds in the presence of β-cyclodextrin

Abstract The pH effects on the 1:1 complexation behavior of β-cyclodextrin (β-CDx) with the title compounds have been investigated by measuring ultraviolet (UV) absorption, circular dichroism (CD), fluorescence and 1 H nuclear magnetic resonance (NMR) spectra and fluorescence lifetimes of the β-CDx inclusion complexes formed. Steric effects of substituent attached at the four position of a guest molecule on the stability of the inclusion complex as well as on the induced CD spectral intensity demonstrated that the guest is included into the β-CDx cavity so as to locate this substituent around the rim of the cavity at low and even at high pH (where a tautomer anion is exclusively produced). The 1 H NMR data were consistent with the intracavity immersion of a given guest molecule from the secondary hydroxy group side and, additionally, substantiated the structure of the β-CDx inclusion complex generated at low pH. Through an analysis of the pH-dependent UV absorption and fluorescence spectra of 7-hydroxycoumarine derivatives, it was found that the proton dissociation abilities of these guests undergo negligible effects of the β-CDx inclusion in both the ground-state and the excited singlet-state. This finding strongly suggested that both the quinoid-type carbonyl and oxido groups in the tautomer anion guest are exposed to the bulk aqueous phase to interact with the surrounding water molecules.

Electron transfer-initiated photocyclization of substituted N-acetyl-α-dehydro(1-naphthyl)alanines to 1,2-dihydrobenzo[f]quinolinone derivatives: Scope and limitations

Abstract The irradiation of substituted N-acetyl-α-dehydro(1-naphthyl)alanines (1) in MeOH containing triethylamine with Pyrex-filtered light gave 1,2-dihydrobenzo[f]quinolinones (2) in preference to benzo[f]isoquinolines (3) and 1-azetines (4). Analysis of substituent effects on the product compositions revealed that the selectivity of 2 has a strong tendency to decrease with increasing steric bulkiness of the alkyl substituent introduced into the starting (Z)-1. From control and fluorescence quenching experiments it was shown that the photocyclization reaction of 1 affording 2 proceeds by an electron-transfer mechanism. The mechanism of this novel cyclization was discussed mainly based on substituent and solvent effects on both the reactivities of the excited singlet-state 1 and the selectivities of the products 2–4.

An efficient transformation of substituted N-acyl-α-dehydro(1-naphthyl)alanines into 1,2-dihydrobenzo[f]quinolinone derivatives via photoinduced intramolecular electron transfer

The irradiation of substituted (Z)-N-acyl-a-dehydro( 1-naphthyl)alanines (1) having the dialkylamino donor on the carboxamide side chain in methanol was found to give 1,2-dihydrobenzo[f]quinolinone derivatives (2) in goodyields, which were formed via the electron-transfer reaction in the excited-state (E)-isomers, while intramolecular photocyclization reactions in the (Z)- and (E)-isomers afforded minor amounts of benzo[f]isoquinolines (3) and 1-azetines (4), respectively. The replacement of the N-acetyl group by the benzoyl (having stronger electron-withdrawing ability and larger steric bulkiness than the former) increased the selectivity for 2 and 4, and this increased selectivity was mainly reflected in a great lowering of that for 3.

Formation of Isoquinoline and 1-Azetine Derivatives via Novel Photocyclization of Substituted α-Dehydrophenylalanines

Abstract The irradiation of substituted N -acetyl α-dehydrophenylalanines in MeOH with Pyrex-filtered light was found to give isoquinoline and 1-azetine derivatives in relatively good yields, which may be formed via intramolecular cyclization reactions from the ( Z )- and ( E )-isomers, respectively. Solvent viscosity effects on the product distribution and composition strongly suggested the minor role of a radical pair mechanism. In the presence of benzophenone as a triplet sensitizer, the starting ( Z )-isomer underwent an exclusive isomerization into the corresponding ( E )-isomer without yielding any cyclization products, being consistent with the occurrence of the novel photocyclization reactions from the excited singlet-state isomers. On the other hand, the irradiation of N -substituted benzoyl α-dehydrophenylalanines in MeOH afforded selectively 1-azetine derivatives without forming any isoquinolines. It was suggested that the stereoelectronic effects of bulky aromatic acyl groups are responsible for the complete suppression of the cyclization reactions, which eventually afford isoquinoline derivatives via the excited singlet-state ( Z )-isomers.

Complexation and fluorescence behavior of diazacrown ether carrying two anthryl pendants.

Photoinduced electron transfer (PET) fluoroionophores (1b, 2b) that consist of diazacrown and two 9-anthryl pendants show fluorescent enhancement with various guest salts. The diaza-12-crown-4 derivative (2b) exhibited Zn(2+) selectivity and in the presence of this cation the host fluorescence intensity was increased by a factor of 182. The guest cation-induced fluorescence enhancement of 2b was larger than the diaza-18-crown-6 derivative (1b).

Complexation and fluorescence behavior of 9,10-bis[bis(β-hydroxyethyl)aminomethyl]anthracene

9,10-Bis[bis(beta-hydroxyethyl)aminomethyl]anthracene (1) showed weak emission, suggesting that photoinduced electron transfer (PET) from amine group to excited anthracene occur. The PET fluoroionophore (1) was found to display unique photophysical properties in the presence of the guest metal cations in H(2)OCH(3)OH (1:1, v/v). Complexation of 1 with guest metal cations increased the fluorescence intensity.

A new route to papaverine analogs via photocyclization of substituted N-acyl-α-dehydrophenylalaninamides

(Z)-N-Phenylacetyl-a-dehydro(3,4-dimethoxyphenyl)alaninamide derivatives [(Z)-1] were prepared in satisfactory yields, starting from 3,4-dimethoxybenzaldehyde. On irradiation in methanol, regioselective photocyclization of these derivatives proceeded to give papaverine analogs in good yields. Substituents introduced into (Z)-1 were found to exert only a minor effect on the conversion of the starting isomers (1) as well as on the selectivity of the analogs which were formed along with 1-azetines.

Simultaneous formation of isoquinoline and 1-azetine derivatives via photoacetyl migration of substituted α-dehydrophenylalanine

Abstract Irradiation of substituted α-dehydrophenylalanine in methanol or acetonitrile with Pyrex-filtered light was found to give isoquinoline and 1-azetine derivatives in relatively good yields, which may be formed via 1,5-acetyl shift from the (Z)-isomer and 1,3-acetyl migration from the (E)-isomer, respectively. The photoreaction in methanol afforded the azetine in preference to the isoquinoline, while the reverse result was obtained in acetonitrile.

Photoinduced electron transfer-initiated enantioselective cyclization of N-benzoyl-α-dehydroarylalanine tert-butyl esters in the presence of chiral amine

The asymmetric photocyclization of the title compounds in 1,2-dichloroethane was found to proceed cleanly in the presence of primary. secondary, or tertiary chiral amine to give the corresponding cis- and trans-3,4-dihydrooxazole derivatives in enantiomeric excess (ee) of 11-38% and 6-33%, respectively, depending on the steric factor of the aryl substituent as well as on the hydrogen-bonding ability of the chiral amine.

Novel photocyclization of substituted α-dehydronaphthylalanines via electron transfer

Irradiation of substituted N-acyl α-dehydro(1-naphthyl)alanines (1) having the dialkylamino donor at the end of a side chain in methanol was found to give 1,2-dihydrobenzo[ƒ]quinolinones (2) in good yields, which were formed via the electron-transfer reaction in the excited-state (E)-isomers, while intramolecular photoaddition reactions in the (Z)- and (E)-isomers afforded minor amounts of benzo[ƒ]isoquinoline (3) and 1-azetine (4) derivatives, respectively. Analysis of substituent effects on the product distribution showed that the bulky diisopropylamino donor as well as the N-benzoy group exerts their effects so as to enhance the relative yield of 3 to 2.