Phytochemistry Reviews 2: 61–85, 2003.
© 2003 Kluwer Academic Publishers. Printed in the Netherlands.
61
Systematics of
2
H patterns in natural compounds and its importance for
the elucidation of biosynthetic pathways
Hanns-Ludwig Schmidt
1,∗
, Roland A. Werner
2
& Wolfgang Eisenreich
3
1
Technische Universität München, Lehrstuhl für Biologische Chemie, An der Saatzucht 5, D-85350 Freising-
Weihenstephan, Germany;
2
Max-Planck-Institut für Biogeochemie, Postfach 10 01 64, D-07701 Jena, Germany;
3
Technische Universität München, Lehrstuhl für Organische Chemie und Biochemie, Lichtenbergstr. 4, D-85747
Garching, Germany;
∗
Author for correspondence (Tel/Fax: +49-(0)871-44497; E-mail: hlschmidt@web.de;
roland.werner@bgc-jena.mpg.de; wolfgang.eisenreich@ch.tum.de)
Key words: aromatic compounds, biosynthetic pathways, carbohydrates, deuterium, fatty acids,
2
H-content,
2
H-
pattern, isoprenoids, isotopes, origin assignment, polyketides
Abstract
The relative global
2
H-content of natural plant products is correlated to that of the primary hydrogen source, i.e.
water, to the site of their biosynthesis (C
3
-, C
4
- and CAM-plants; chloroplasts, cytosol), and to their biosynthetic
pathways. A relative global
2
H-content sequence can be established in the order phenylpropanoids > carbohydrates
> bulk material > hydrolysable lipids > steroids. A detailed analysis of the
2
H-patterns of the main groups of
secondary compounds reveals regularities, in that they are correlated to the primary precursors and to the origin of
hydrogen from four main pools with the mean δ
2
H-values []
V−SMOW
: leaf H
2
O ∼+30; carbohydrates ∼−70;
NADPH ∼−250; flavoproteins ∼−350. Aside from the
2
H-discrimination between these pools, kinetic isotope
effects on defined reactions only become effective in connection with metabolic branching events. So, the
2
H-
pattern of natural aromatic compounds can be correlated to the
2
H-pattern of the precursor carbohydrates and a
reduction step in the course of the shikimic acid pathway, furthermore to the implication of the NIH-shift. The
pattern of aromatic compounds from the polyketide is different from that of the shikimate pathway. The alternating
2
H-abundance of fatty acid chains is caused by the origin of their hydrogen atoms from carbohydrates and from
NADPH, directly or via a flavoprotein, respectively. This is similar for isoprenoids, and the natural
2
H-patterns
permit their assignment to the mevalonate or non-mevalonate biosynthetic pathway. Generally, the correlations
and regularities of the
2
H-patterns of organic compounds found are a new reliable tool for the elucidation of
biosynthetic pathways and origin assignments.
Abbreviations: NIH-shift – a shift of an H-atom from the p- to the m-position in context with the p-hydroxylation
of an aromatic compound, first described by a group of the N ational I nstitutes of H ealth.
Introduction
The non-statistical distribution of the isotopes of the
bio-elements in natural organic matter has been a
generally accepted phenomenon for many years. The
global isotope abundances of biomass and of defined
natural compounds, and the isotopic patterns of the
latter are used to correlate them to their origin and
to discriminate them from synthetic analogues. Car-
bon isotope patterns can only be obtained by laborious
degradations of organic molecules (Schmidt et al.,
1995), while deuterium patterns are directly available
by means of
2
H NMR (Martin et al., 1992; Martin,
1995; Martin and Martin, 1999). To date, applica-
tions in the field of flavour origin and authenticity
determinations have been performed predominantly
and empirically on the basis of authentic reference