Miyoko Kamigauchi

Guest-dependent conformation of 18-crown-6 tetracarboxylic acid: Relation to chiral separation of racemic amino acids

(+)-18-crown-6 tetracarboxylic acid (18C6H(4)) has been used as a chiral selector for various amines and amino acids. To further clarify the structural scaffold of 18C6H(4) for chiral separation, single crystal X-ray analysis of its glycine(+) (1), H3O+ (2), H5O2+ (3), NH4+ (4), and 2CH3NH3+ (5) complexes was performed and the guest-dependent conformation of 18C6H(4) was investigated. The crown ether ring of 18C6H4 in 3, 4, and 5 took a symmetrical C2 or C2-like conformation, whereas that in 1 and 2 took an asymmetric C1 conformation, which is commonly observed in complexes with various optically active amino acids. The overall survey of the present and related complexes suggests that the molecular conformation of 18C6H4 is freely changeable within an allowable range, depending on the molecular shape and interaction mode with the cationic guest. On the basis of the present results, we propose the allowable conformational variation of 18C6H4 and a possible transition pathway from its primary conformation to the conformation suitable for chiral separation of racemic amines and amino acids.

Structural scaffold of 18-crown-6 tetracarboxylic acid for optical resolution of chiral amino acid: X-ray crystal analyses and energy calculations of complexes of D- and L-isomers of tyrosine, isoleucine, methionine and phenylglycine

To clarify the structural scaffold of (+)-18-crown-6 tetracarboxylic acid ((+)-18C6H4) for the optical resolution of a chiral amino acid, the crystal structures of its equimolar complexes with L- and D-isomers of tyrosine (Tyr), isoleucine (Ile), methionine (Met) and phenylglycine (PheG) were analysed by X-ray diffraction methods. (+)-18C6H4 took very similar conformations for all complexes. Although the chemical structure of (+)-18C6H4 is C2-symmetric, it took a similar asymmetric ring conformation of radius ca. 6.0 A. In all complexes, the amino group of chiral amino acids was located near the center of the ring and formed three hydrogen bonds and five electrostatic interactions with eight oxygen atoms of the ether ring and carboxyl groups. Also, the Calpha atom of chiral amino acids participated in Calpha-H...O interaction with the oxygen atom of (+)-18C6H4. In contrast, the carboxyl group of chiral amino acids did not directly interact with (+)-18C6H4. These results indicate that the structural scaffold of (+)-18C6H4 for the optical resolution of chiral amino acids is mainly based on the mode of interaction of (+)-18C6H4 with the amino and Calpha-H groups of chiral amino acids. The differences in interaction pattern and binding energy between the L- and D-isomers of each amino acid are discussed in relation to the chiral recognition of (+)-18C6H4.

Biotransformation of phenolic tetrahydroprotoberberines in plant cell cultures followed by LC-NMR, LC-MS, and LC-CD.

A metabolic pathway of 2,3,10,11-oxygenated tetrahydroprotoberberines having the OH group on ring D was demonstrated. Metabolism of (13)C- or D(2)-labeled precursors was studied in cell cultures of Macleaya, Corydalis, and Nandina species. The structures of alkaloid metabolites obtained from feeding experiments were determined by application of combined LC-NMR, LC-MS/MS, and LC-CD techniques. (S)-Tetrahydropseudoprotoberberine (5) was stereospecifically O-methylated to the S-isomer (12) in cell cultures of three plant species. This S-isomer was further N-methylated to the (S)-alpha-N-methyl salt (15), which was oxidized to produce the pseudoprotopine-type alkaloid (10) in cell cultures of Macleaya and Corydalis species. These transformations were the same as those of 2,3,9,10-oxygenated protoberberines. The tetrahydropseudoprotoberberines (5, 6, and 12) were dehydrogenated to pseudoprotoberberines (13, 16, and 14), respectively. Both the R- and S-enantiomers of 5 were dehydrogenated in Macleaya cordata different from the case of 2,3,9,10-oxygenated protoberberines. Precursor 7, with OH groups at C-10 and C-11, was O-methylated at C-10 in M. cordata and C. ochotensis var. raddeana, which was distinct from O-methylation in N. domestica, in which 7 was O-methylated at both C-11 and C-10. Stereoselective O-demethylation [(S)-5 to (S)-18] occurred in N. domestica.

13-Hydroxylation of tetrahydroberberine in cell suspension cultures of some Corydalis species

Liquid chromatography/atmospheric pressure chemical ionization-mass spectrometry was applied to biotransformation experiments in cultured cells of Corydalis ophiocarpa as well as C. ochotensis var. raddeana. Hydroxylation at C-13 of tetrahydroberberine was shown to take place in cell cultures as well as in C. ophiocarpa plants. N-Methylation of tetrahydroberberine occurred to form the α-N-metho salt incorporating the B/C-cis-quinolizidine system. Introduction of the C-13 methyl with berberine as substrate was confirmed to provide 13-methylberberine. In addition, the reversible oxidation-reduction of the C ring of protoberberines was demonstrated.

Formation of benzo[c]phenanthridines by oxidative CN bond fission of protoberberines followed by intramolecular recyclization in cell cultures of corydalis incisa

Abstract Only 9 of the 6-hydroxy-13-methylprotoberberine N-metho salts 9 and 10 was transformed by cell cultures of C. incisa into the benzo[ c ]phenanthridines, corynoline ( 1 ) and corynoloxine ( 2 ). Corycavine ( 7 ) was incorporated more effectively into 1 and 2 than 9 .

O-Methylating Enzymes of Dopamine and Dopamine Derived Tetrahydroisoquinoline, Salsolinol

Abstract By using an LC/API-MS system, it was demonstrated that dopamine condenses with acetaldehyde to give salsolinol which is further metabolized to produce

Metabolism of salsolinol by tissue cultures of some Papaveraceae

Abstract (±)-Salsolinol, a substance possibly inducing Parkinsonism and alcoholism, was transformed into the 6-and 7- O -monomethylated salsolinols by various plant tissue cultures of the Papaveraceae. Only 6- O -methylsalsolinol was further N -methylated to provide N -methylisosalsoline.

Conformational analysis of the cyclised pyridoxal Schiff base of L-tryptophan. X-Ray crystal structure, nuclear magnetic resonance and molecular orbital studies of 3-carboxy-1-{3-hydroxy-2-methyl-5-[(phosphonooxy)methyl]-4-pyridyl}-1,2,3,4-tetrahydro-β-carboline

In order to deduce the structural features of cyclised Schiff bases in their in vivo regulation of pyridoxal-requiring enzymes, the molecular conformation of 3-carboxy-1-{3-hydroxy-2-methyl-5-[(phosphonooxy)methyl]-4-pyridyl}-1,2,3,4-tetrahydro-β-carboline, a cyclised Schiff base between pyridoxal 5-phosphate and L-tryptophan, has been investigated by X-ray crystal analysis, 1H NMR measurements and molecular orbital calculations. In the crystalline state the molecule, which is in a double zwitterionic state with the hydroxy and phosphate oxygen atoms deprotonated and the pyridine and β-carboline nitrogen atoms protonated, takes a rigid conformation stabilized by two intramolecular hydrogen bonds between the carboline NH and pyridoxal O– and between the indole NH and phosphate O– atoms. This solid conformation also appears to be the preferred conformation in DMSO solution, as judged from appreciable ROEs between protons and J values. Conformational analysis by CNDO/2 calculations showed the conformation observed in the crystal also to be energetically the most favourable. The importance of this molecular conformation for the biological function of the cyclised Schiff base is discussed.

Effects of Pyrogallol on O-Methylation of Dopamine and Salsolinol

In the cultured cells of Corydalis pallida var. tenuis, the formation of 6-O-methylated metabolites (6-D4 and 6-D7) from salsolinol-D4 (2-D4) was reduced by pyrogallol. The production of 3-O-methylated derivatives (10 and 10-D3) from dopamine was almost not affected by pyrogallol. Similar results were obtained in intact plants, though the effect of pyrogallol on methylation of C-6-OH of salsolinol in plants is smaller than that in the cultured cells. These results show that the effects of pyrogallol on the methylation of C-6-OH of salsolinol and that on the methylation of C-3-OH of dopamine are different, suggesting that the O-methylating enzymes of salsolinol and dopamine are different in C. pallida var. tenuis. The production of 3-O-methyldopamine in the presence of pyrogallol was reduced in intact plants of Cynanchum vincetoxicum, but not in the cultured cells. The effect of pyrogallol on the methylation of salsolinol was uncertain in Cyn. vincetoxicum. Both 6- and 7-O-methylations of salsolinol occur in Cyn. vincetoxicum, while only 6-O-methylation occurs in C. pallida var. tenuis. This could reveal that the O-methylating enzymes at C-6 and C-7 are different.

1 H NMR and X-ray conformational analyses of (+)-corydalic acid methyl ester, a 6,7-secoberbine alkaloid

Conformational analysis of (+)-corydalic acid methyl ester (1) by 1H NMR data indicated that 1 in chloroform solution at room temperature exists in a conformational equilibrium. The NOEs in the NOESY spectra of 1 and the temperature dependence of the NMR spectral pattern suggested that rotation of the ring A moiety around the C(14)–C(15) bond is obstructed by two neighbouring methyl groups on the N(7) and C(13) positions. The structure of 1 was determined to be methyl (6R-trans)-6-(6,7,8,9-tetrahydro-6,8-dimethyl-1,3-dioxolo[4,5-h]isoquinolin-7-yl)-1,3-benzodioxole-5-acetate by X-ray crystal structure analysis. The crystal conformer of 1 agrees well with one of the two stable conformers derived from NMR analysis and empirical energy calculations. The function of 6,7-secoberbine type alkaloids for the biosynthetic pathway from protoberberine type into the hexahydrobenzo[c]phenanthridine type is discussed in relation to their conformational features.