ABSTRACT

References..............................................................................................................290

Betalains are N-heterocyclic water-soluble pigments deposited in vacuoles. Their common precursor is betalamic acid consisting of a 1,7-diazaheptamethin system, an extended π-electron system exhibiting a canary yellow color. Betalamic acid may condense with cyclo-dopa to yield betanidin, the common precursor aglycon of the red betacyanins. Betanidin in turn may be glycosylated and/or acylated, yielding 29

genuine structures known to date. Due to stereoisomerism at C15 their number is doubled, except for neobetanin (14,15-dehydrobetanin) which is devoid of the chiral center at C-15.1

The yellow analogues, the betaxanthins, are composed of betalamic acid with amino acids or amines, respectively, amounting to 26 structures known to occur naturally.2-4 Structures unambiguously assigned by NMR spectroscopy usually carry trivial names derived from the plant material from which they have been first isolated. The substitution patterns of betalyanins and betaxanthins hitherto reported together with their particular plant sources are listed in Table 4.4.1 and 4.4.2, respectively.