ABSTRACT
References ........................................................................................................................ 1058
Appendix A ...................................................................................................................... 1070
Appendix B ...................................................................................................................... 1071
The chalcones, dihydrochalcones, and aurones are three distinctive classes of compound that
comprise more than 900 of all the naturally occurring flavonoids reported in the literature to
historical perspective, the chalcones and aurones are best
known as the yellow to orange colored flower pigments of some species of Coreopsis and
other Asteraceae taxa. The distribution of these compounds is not restricted to flowers,
however, and examples of all three classes can be found in many different plant tissues. The
chalcones are structurally one of most diverse groups of flavonoids, as witnessed by the
formation of a wide range of dimers, oligomers, Diels-Alder adducts, and conjugates of
various kinds. At the same time, they are of great significance biosynthetically as the
immediate precursors of all other classes of flavonoid. Underlying these important attributes
is the unique feature that distinguishes chalcones and dihydrochalcones from other flavo-
noids, the open-chain three-carbon structure linking the A-and B-rings in place of a hetero-
cyclic C-ring (Figure 16.1). In plants, chalcones are converted to the corresponding (2S)-
flavanones in a stereospecific reaction catalyzed by the enzyme chalcone isomerase. This close
structural and biogenetic relationship between chalcones and flavanones explains why they
often co-occur as natural products. It is also the reason why chalcones, dihydrochalcones, and
aurones are sometimes described together with flavanones and dihydroflavonols.1-3 Whether
this group should continue to be known as the ‘‘minor flavonoids’’ is a matter for debate;
however, the significant increase in the number of new examples of each of these flavonoid
classes in the recent literature suggests that this title may no longer be appropriate. For this
reason, the chalcones, dihydrochalcones, and aurones are treated separately from the flava-
nones and dihydroflavonols (Chapter 15) in this volume. The main purpose of this chapter is
to review the scientific literature on all chalcones, dihydrochalcones, and aurones reported as
new natural products during the period from 1992 to 2003. This continues the tradition set by
the four volumes of the Advances in Flavonoids series,1-4 which provide the most comprehen-
sive treatment available of the scientific literature relating to flavonoids up to the end of 1991.
It is not the purpose of this review to describe general methods for the detection, isolation,
and characterization of chalcones, dihydrochalcones, and aurones, as these have been dis-
cussed extensively not only in the ‘‘Advances’’ series1-4 but also in more general texts on
flavonoids.5-10 However, points of interest relating to the source, identification, and bio-
logical activity of new compounds are covered, as well as wider issues such as biosynthesis
and chemosystematic or ecological significance. The chemical synthesis of these three flavo-
noid classes (a major subject in its own right) is not treated here, although synthetic proced-
