314
Y. Bai et al.
5.2
Nuclear Magnetic Resonance Spectroscopy . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 332
6
Conclusions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 333
References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 334
1 Introduction
Natural products, also known as “secondary metabolites,” are a class of chemical
compounds that are produced by certain living organisms. Not only those compounds
generated from living organisms (such as bacteria, fungi, or plants) are natural products, but many human endogenous biochemicals, including trace amines and fatty
acid derivatives, are also natural products based on their definition. Besides these
endogenous natural products produced by human cells, the human microbiome
also produces natural products, as elucidated by the Human Microbiome Project
(HMP) [1]. As a result of recent achievements made in metabolomics research and
from the HMP, some previously accepted information has been corrected regarding
endogenous natural products. Therefore, this contribution will describe the current
understanding and the recent progress made on endogenous natural products that are
produced by human cells and symbiotic microbes.
2 Endogenous Natural Products
2.1 Endogenous Amines
2.1.1 Catecholamines
Neurotransmitters are essential for the functioning of the nervous system, and many
endogenous amines (e.g., catecholamines) work as neurotransmitters [2]. Catecholamines, including dopamine, norepinephrine, and epinephrine, are key chemical neurotransmitters and hormones that regulate physiological processes. The
biosynthesis of catecholamines starts from tyrosine. First, tyrosine is 3-hydroxylated
to form l-DOPA. Next, aromatic acid decarboxylase (AADC) transforms lDOPA to the first catecholamine (dopamine). The second catecholamine (norepinephrine) is the β-hydroxylation product of dopamine. Finally, phenylethanolamine
N-methyltransferase (PNMT) converts norepinephrine into epinephrine [3] (Fig. 1).
Although related metabolic research is extensive, misunderstandings in the area
occur because of limitations in the experimental protocols used previously. Studies
in the last 30 years have permitted the construction of a more accurate atlas for the
disposition and metabolism of catecholamines than before. The deamination of norepinephrine and epinephrine by monoamine oxidase (MAO) yields the reactive aldehyde 3,4-dihydroxyphenylglycolaldehyde (DOPEGAL), which is reduced to form
Y. Bai et al.
5.2
Nuclear Magnetic Resonance Spectroscopy . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 332
6
Conclusions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 333
References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 334
1 Introduction
Natural products, also known as “secondary metabolites,” are a class of chemical
compounds that are produced by certain living organisms. Not only those compounds
generated from living organisms (such as bacteria, fungi, or plants) are natural products, but many human endogenous biochemicals, including trace amines and fatty
acid derivatives, are also natural products based on their definition. Besides these
endogenous natural products produced by human cells, the human microbiome
also produces natural products, as elucidated by the Human Microbiome Project
(HMP) [1]. As a result of recent achievements made in metabolomics research and
from the HMP, some previously accepted information has been corrected regarding
endogenous natural products. Therefore, this contribution will describe the current
understanding and the recent progress made on endogenous natural products that are
produced by human cells and symbiotic microbes.
2 Endogenous Natural Products
2.1 Endogenous Amines
2.1.1 Catecholamines
Neurotransmitters are essential for the functioning of the nervous system, and many
endogenous amines (e.g., catecholamines) work as neurotransmitters [2]. Catecholamines, including dopamine, norepinephrine, and epinephrine, are key chemical neurotransmitters and hormones that regulate physiological processes. The
biosynthesis of catecholamines starts from tyrosine. First, tyrosine is 3-hydroxylated
to form l-DOPA. Next, aromatic acid decarboxylase (AADC) transforms lDOPA to the first catecholamine (dopamine). The second catecholamine (norepinephrine) is the β-hydroxylation product of dopamine. Finally, phenylethanolamine
N-methyltransferase (PNMT) converts norepinephrine into epinephrine [3] (Fig. 1).
Although related metabolic research is extensive, misunderstandings in the area
occur because of limitations in the experimental protocols used previously. Studies
in the last 30 years have permitted the construction of a more accurate atlas for the
disposition and metabolism of catecholamines than before. The deamination of norepinephrine and epinephrine by monoamine oxidase (MAO) yields the reactive aldehyde 3,4-dihydroxyphenylglycolaldehyde (DOPEGAL), which is reduced to form