Orthophosphoric acid has been found to accomplish the previously unsuccessful oyclization of azomethines of 3-formylcarbazoles and aminoacetal to substituted pyrido[4,3-b]carbazoles according to a scheme proposed by Cranwell and Sexton. By this method, there have been prepared 6,ll-dimethyl-(ellipticine), 5,6,11trimethyl-, 5,9,11-trimethyl-, 9-methoxy-5,ll-dimethyl-(9-methoxyellipticine), 9-methoxy-5,6,11-trimethyl-, 9-bromo-6,ll-dimethyl-, and 9-nitro-5,ll-dimethyl-6H-pyrido[4,3-blcarbazole.
The fine structures of 4-amino-6-hydroxy-,
4-amino-6-mercapto-, 4-amino-2-mercapto-, 2-amino-4-hydroxy-, and
2-amino-4-mercapto-pyrimidine are revealed by comparing their ultraviolet
spectra and ionization constants with those of their S- and 0-, or N- and
S-methyl derivatives. On the evidence here presented they appear to exist
largely in aqueous solution as the tautomers containing an amino group, namely:
4-amino-1,6-dihydro-6-oxopyrimidine, 4-amino-1,6-dihydro-6-thiopyrimidine,
4-amino-1,2(and 2,3)-dihydro-2-thiopyrimidine, 2-amino-1,4(and
3,4)-dihydro-4-oxopyrimidine, and 2-amino-1,6-dihydro-6-thiopyrimidine,
respectively. Syntheses of hitherto unknown methyl derivatives are recorded.
Cyclodehydration in
orthophosphoric acid of the azomethines of 3- formyl-carbazoles and
aminoacetals has yielded 5-methyl- (IId), 3,5,11-
trimethyl-(11b), 3,5,9,11-tetramethyl-(IIc), and
5,7,10,11-tetramethyl- 6H-pyrido[4,3-b]carbazoles (IIa).
In the same way γ-carboline and 6,9- dimethyl-γ-carboline were
obtained from the azomethines of 3-formyl- and 3-formyl-4,7-dimethyl-indole. A Doebner reaction with 3-amino-2- methylcarbazole, acetaldehyde,
and pyruvic acid yielded 1-carboxy-3,5- dimethyl-7H-pyrido[2,3-c]carbazole (VIIIb) from which was derived the methyl ester (VIIIc) and 3,5-dimethyl-7H-pyrido [2,3-c]carbazole (VIIIa).
Stability constants for the
Mg2+, Ca2+, Cu2+ and Zn2+ complexes
of two isomers (2) and (3) of the defleecing agent mimosine (1) have been
sought from potentiometric titrations in aqueous
solution, 0.15 M KNO3, at 37°. For the interpretation of the
results, complex formation of the simpler ligands 3-hydroxypyridin-4(1H)-one
(4), its 2-oxo isomer (5) and
DL-α-amino-β-(6-oxo-1,6-dihydropyridin-2-yl)propanoic acid (6) was
studied. The results with ligand (2) are very similar to those with mimosine,
for which a computer blood-plasma model indicates metal chelation under
physiological conditions. Ligand (3) is a much weaker complexing agent.
Complex formation of the
biologically active amino acid L-mimosine [α-amino-β-(3-hydroxy-4-oxo-1,4-dihydropyridin-1-yl)propanoic
acid (1)], mimosinic acid (2), mimosine methyl ether (9) and
3-hydroxy-1-methylpyridin-4(1H)-one
(4) with Cu2+, Zn2+, Cd2+ and Pb2+
was studied. Stability constants were determined by potentiometric titration in
0.15M KNOB3 as inert electrolyte at 37�. In the monomeric
complexes formed by the mimosine derivatives, metal binding by the hydroxypyridone
moiety was favoured relative to the amino acid group. With mimosine, dimeric
complexes were major species. Under physiological conditions, mimosine binds
copper and zinc ions more strongly than do simpler amino acids.
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