3.4- Dihydroxyphenylethylamine dopamine

Alkaloids possessing the 1-benzylisoquinoline skeleton are biosynthesized from two molecules of tyrosine, which are differentiated at the beginning of the biosynthetic pathway. Namely, the isoquinoline moiety, except for one carbon, originates from 3, 4 -dihydroxyphenylethylamine (dopamine), which is formed from tyramine following the decarboxylation of tyrosine. The other part of the alkaloid is derived from 4 -hydroxyphenylac-etaldehyde, which is formed from tyrosine via 4 -hydroxyphenyl pyruvic acid. These two compounds are coupled stereoselectively to give (S)-norcoclaurine. (S)-Norcoclaurine is transformed into (S)-coclaurine by 6-O-methylation, and further N-methylation, hydroxylation at the... 

Isoquinoline alkaloids are derived from tyrosine through the intermediacy of 3,4-dihydroxyphenylethylamine (dopamine) and a carbonyl unit of various origins. The genesis of tyramine, and dopamine from tyrosine has been described previously (see Chapter 28). In contrast to benzylisoquinoline alkaloids (see below), the formation of isoquinoline alkaloids usually involves the amine and an a-ketoacid instead of an amine and aldehyde. However, several compounds can... 

The order of methoxylation and oxidation steps varies. In some instances, the 3,4-dihydroxyphenylethylamine (dopamine) precursor may be modified before condensation occurs. Despite their structural similarity, pellotine (2) and anhalamine (1) are probably synthesized along distinct pathways from mescaline (4). All three alkaloids co-occur in Lophophora williamsii. 

The similar treatment in the presence of chlorogenic acid produced the modified chitosan soluble imder both acidic and basic conditions (311). On the other hand, the tyrosinase-catalyzed reaction of 3,4-dihydroxyphenylethylamine (dopamine) provided water-resistant adhesive properties to chitosan (312). A chitosan derivative modified with hydroxy or dihydroxybenzaldehyde was cross-linked by tyrosinase to give stable and self-sustaining gels (313). Phenolic moiety of a synthetic polymer, poly(p-hydroxystyrene), was also subjected to tyrosinase-catalyzed oxidation (314). 

A, adrenaline COMT, catechol-O-methyl transferase CSF, cerebrospinal fluid DA, 3,4-dihydroxyphenylethylamine (dopamine) Dopa, 3,4-dihydroxyphenylalanine 5HIAA, 5-hydroxyindoleacetic acid 5HT, 5-hydroxytryptamine (serotonin) 5HTP, 5-hydroxytryptophan HVA, 3-methoxy-4-hydroxyphenylacetic acid (homovanillic acid) MAO, monoamine oxidase MAOI, monoamine oxidase inhibitor MHPG,... 

Dopamine (3 4 dihydroxyphenylethylamine), like noradrenaline and adrenaline, is a eateeholamine and in addition to its independent neurotransmitter role in the CNS it is a preeursor to noradrenaline (NA) in all central and peripheral noradrenegic neurons. 

Histamine, serotonin and the catecholamines (dopamine, epinephrine and norepinephrine) are synthesized from the aromatic amino acids histidine, tryptophan and phenylalanine, respectively. The biosynthesis of catecholamines in adrenal medulla cells and catecholamine-secreting neurons can be simply summarized as follows [the enzyme catalysing the reaction and the key additional reagents are in square brackets] phenylalanine — tyrosine [via liver phenylalanine hydroxylase + tetrahydrobiopterin] —> i.-dopa (l.-dihydroxyphenylalanine) [via tyrosine hydroxylase + tetrahydrobiopterin] —> dopamine (dihydroxyphenylethylamine) [via dopa decarboxylase + pyridoxal phosphate] — norepinephrine (2-hydroxydopamine) [via dopamine [J-hydroxylasc + ascorbate] —> epinephrine (jV-methyl norepinephrine) [via phenylethanolamine jV-methyltransferase + S-adenosylmethionine]. 

A third major group, including emetine and a series of structurally related alkaloids, involves condensation of the same amine precursor (3,4-dihydroxyphenylethylamine or dopamine) with a carbonyl group from secologanin—an iri-doid monoterpene precursor. Most of these compounds have been isolated from two families, the Rubiaceae and the Alan-giaceae. 

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