189
12
However, latex-containing laticifers are also found in the stem. A derivative of thebaine is
oripavine, which is also an opiate.
In Ranunculaceae, as analysed in Thalictrum flavum (meadow-rue), the benzylisoquinoline alkaloid metabolism takes place in endodermis, pericycle, protoderm, cortex or
pith tissues and does not involve vascular cell types as in Papaveraceae (Bird et al. 2003;
Samanani et al. 2005; Samanani et al. 2006).
Apparently, morphine can also be synthesized in mammalian tissues. The presence
of common intermediates of morphine biogenesis between plants and mammals suggests analogous pathways. Several enzymes for morphine synthesis have been identified
in mammals, for instance, an enzyme catalyzing the conversion of thebaine into morphine. Dopamine seems to be the precursor for morphine in mammals. This suggests that
trace amounts of morphine and related alkaloids can be produced in animals and are not
always taken up with dietary plants (Laux-Biehlmann et al. 2013; Kramlinger et al. 2015).
Bicuculline, another isoquinoline alkaloid the biosynthesis pathway of which is not yet
understood, has been isolated from Fumariaceae such as Corydalis. It acts as an antagonist
of GABA A receptors, thereby mimicking epilepsy (Johnston 2013).
12.4 Phenethylamine Alkaloids (Derived from Tyrosine,
e.g. Mescaline)
Tyramine (derived from tyrosine) is also the starting point for phenethylamine alkaloids
or monoamine alkaloids. Tyramine itself is unable to cross the blood-brain barrier, and
therefore does not have any psychoactive effects after ingestion. Hordenine is synthesized
by the stepwise N-methylation of tyramine, which is first converted to N-methyltyramine,
and which, in turn is methylated to hordenine. This compound was first isolated from the
cactus Ariocarpus fissuratus, but later also from barley (Hordeum vulgare) seedlings. It can
act as an allelochemical repressing growth and germination of plants in the surrounding.
Hordenine is sold as a nutritional supplement with claims that it would stimulate the central nervous system and promote weight loss by enhancing metabolism. However, there is
no scientific evidence for such effects.
When tyramine is hydroxylated it yields 2-DOPA (L-dihydroxyphenylalanine) and
carboxylation then creates dopamine. Dopamine can be further methylated and hydroxylated (. Fig. 12.4). This results in the production of mescaline, a psychedelic alkaloid,
which can be isolated from several cacti, such as the South American peyote cactus
(Lophophora williamsii). In humans dopamine gives rise to the catecholamines, noradrenaline and adrenaline (epinephrine). These animal hormones and neurotransmitters are
also produced in some plants, for instance, dopamine is found in in the pulp of banana
(Musa acuminata), plantain (green or cooking bananas, Plantago major) and the fruit of
avocado (Persea americana) (Kulma and Szopa 2007; Soares et al. 2014).
12.5 Phenylethylamine (Derived from Phenylalanine,
e.g. Ephedrine)
When only the carbon skeleton of phenylalanine is utilized and transformed into
1- phenyl-1,2-propanedione and then transaminated, cathinone is formed. This component can be found in Khat (Catha edulis, Celastraceae) and acts as an amphetamine-like
12.5 · Phenylethylamine (Derived from Phenylalanine, e.g. Ephedrine)
12
However, latex-containing laticifers are also found in the stem. A derivative of thebaine is
oripavine, which is also an opiate.
In Ranunculaceae, as analysed in Thalictrum flavum (meadow-rue), the benzylisoquinoline alkaloid metabolism takes place in endodermis, pericycle, protoderm, cortex or
pith tissues and does not involve vascular cell types as in Papaveraceae (Bird et al. 2003;
Samanani et al. 2005; Samanani et al. 2006).
Apparently, morphine can also be synthesized in mammalian tissues. The presence
of common intermediates of morphine biogenesis between plants and mammals suggests analogous pathways. Several enzymes for morphine synthesis have been identified
in mammals, for instance, an enzyme catalyzing the conversion of thebaine into morphine. Dopamine seems to be the precursor for morphine in mammals. This suggests that
trace amounts of morphine and related alkaloids can be produced in animals and are not
always taken up with dietary plants (Laux-Biehlmann et al. 2013; Kramlinger et al. 2015).
Bicuculline, another isoquinoline alkaloid the biosynthesis pathway of which is not yet
understood, has been isolated from Fumariaceae such as Corydalis. It acts as an antagonist
of GABA A receptors, thereby mimicking epilepsy (Johnston 2013).
12.4 Phenethylamine Alkaloids (Derived from Tyrosine,
e.g. Mescaline)
Tyramine (derived from tyrosine) is also the starting point for phenethylamine alkaloids
or monoamine alkaloids. Tyramine itself is unable to cross the blood-brain barrier, and
therefore does not have any psychoactive effects after ingestion. Hordenine is synthesized
by the stepwise N-methylation of tyramine, which is first converted to N-methyltyramine,
and which, in turn is methylated to hordenine. This compound was first isolated from the
cactus Ariocarpus fissuratus, but later also from barley (Hordeum vulgare) seedlings. It can
act as an allelochemical repressing growth and germination of plants in the surrounding.
Hordenine is sold as a nutritional supplement with claims that it would stimulate the central nervous system and promote weight loss by enhancing metabolism. However, there is
no scientific evidence for such effects.
When tyramine is hydroxylated it yields 2-DOPA (L-dihydroxyphenylalanine) and
carboxylation then creates dopamine. Dopamine can be further methylated and hydroxylated (. Fig. 12.4). This results in the production of mescaline, a psychedelic alkaloid,
which can be isolated from several cacti, such as the South American peyote cactus
(Lophophora williamsii). In humans dopamine gives rise to the catecholamines, noradrenaline and adrenaline (epinephrine). These animal hormones and neurotransmitters are
also produced in some plants, for instance, dopamine is found in in the pulp of banana
(Musa acuminata), plantain (green or cooking bananas, Plantago major) and the fruit of
avocado (Persea americana) (Kulma and Szopa 2007; Soares et al. 2014).
12.5 Phenylethylamine (Derived from Phenylalanine,
e.g. Ephedrine)
When only the carbon skeleton of phenylalanine is utilized and transformed into
1- phenyl-1,2-propanedione and then transaminated, cathinone is formed. This component can be found in Khat (Catha edulis, Celastraceae) and acts as an amphetamine-like
12.5 · Phenylethylamine (Derived from Phenylalanine, e.g. Ephedrine)