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2,3‐ and 4,5‐Secodopa, the Biosynthetic Intermediates Generated from L ‐Dopa by an Enzyme System Extracted from the Fly Agaric, Amanita muscaria L., and Their Spontaneous Conversion to Muscaflavin and Betalamic Acid, Respectively, and Betalains
Author(s) -
Terradas Fernand,
Wyler Hugo
Publication year - 1991
Publication title -
helvetica chimica acta
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.74
H-Index - 82
eISSN - 1522-2675
pISSN - 0018-019X
DOI - 10.1002/hlca.19910740115
Subject(s) - chemistry , enzyme , stereochemistry , betalain , proline , amino acid , salt (chemistry) , high performance liquid chromatography , organic chemistry , biochemistry , pigment
An enzyme is extracted from the red peel of Amanita muscaria which cleaves the C(2)–C(3) and the C(4)–C(5) bond of the aromatic ring of L ‐dopa ( 1 ) to form a mixture of 4,5‐secodopa (= salt of 6‐amino‐2‐hydroxy‐4‐(2′‐oxoethylidene)hept‐2‐enedioic acid; 2 ) and 2,3‐secodopa ( = salt of 7‐amino‐5‐formyl‐2‐hydroxyocta‐2,4‐dienedioic acid; 3 ), two hitherto hypothetical biosynthetic intermediates (see Scheme ). Though isolation of these products has not been possible, structural evidence is inferred from reaction products, kinetics, and spectroscopical characteristics in comparison with known compounds. Secodopas 2 and 3 are characterized in dilute solution by HPLC and UV/VIS spectroscopy (anions; λ max 424 and 414 nm, resp., ϵ 420 = 25500; on acidification, shift to 380 and 372 nm, resp.). They cyclize without enzyme catalysis, optimally at pH 4.5–5; 3 produces muscaflavin ( 5 ) and 2 betalamic acid ( 4 ). The products arc identified by direct comparison with authentic samples in HPLC, by 1 H‐NMR of 5 , and by condensation of 4 with L ‐proline to form the well known betalain indicaxanthin ( 7 ). The enzymatic conversion of L ‐dopa ( 1 ) via 2 to betalamic acid ( 4 ; ( S )) and its condensation with L ‐proline leads to pure natural indicaxanthin ( 7 ; (2 S ,11 5 )); correspondingly, the enzymatic conversion of D ‐dopa to ( R )‐betalamic acid and its condensation with L ‐proline produces isoindicaxanthin ((2 S ,11 R )) which is unknown in nature. Particularly relevant is the fact that the same enzyme cleaves pyrocatechol to produce a solution of the enolate form of the known 2‐hydroxy‐6‐oxohexa‐2,4‐dienoate (secopyrocatechol; 9 ; see Fig. 5 ). Dissociation constants of the corresponding enolic functions in the cleavage products are determined by spectrometric titration and compared to those of known systems.