Ghp

  1. Gallates linked respectively through ester and anhydride groups GesG and GanG
  2. Neolignans and lignans: see addenda to Table 5.
  3. Stilbenoids: stilbenes 1,2-phenylbenzofurans 2, dihydrostilbenes 3.
  4. Other: allylphenols All, anthraquinones Ant, phenylethylcinnamates Pec, acetophenones Ace, naphthoquinones Nap, cou-marins Cou, styrenes Sty, dihydrophenanthrenes Dhp, spiroindans Spi, phloroglucinols Phi, tcrpcnoolivctols Toi, C-prenylated phenolics cp.

2 cp

3 Dhp Spi Phi Toi cp

in the Moraceae, a family endowed with a comparatively rich palate of flavonoids not only because of the presence of a considerable number of structural types, including diarylpropanes and isoflavones, but chiefly on account of the exceptional number of oxygenation patterns. Indeed, in all other families here associated with the Hamamelidae, rather traditional flavonoid oxygenation patterns are observed throughout. Proanthocyanidins are uniformly present in nearly all families. Should their absence in the Cecropiaceae be confirmed, a relatively advanced position would have to be conferred to this family.

Gallic Acid Derivatives (Table 9). The structural elucidation of the so-called gallotannins, having achieved technical feasibility only in recent times, has not yet provided a chemosystematically significant number of data. As far as known at the time of writing, the widespread G, GG, and GGOG aglyconic structural units are accompanied by moieties with three or four oxidatively linked galloyls in the Betula-ceae, Fagaceae, and Myricaceae, while the much more restricted H (dehydrotetrahydroxydiphenoyl) moieties occur in the Cercidiphyllaceae and Betula-ceae. Galloyl units linked by ester (depsides) and anhydride functions are accumulated pereferentially by the Betulaceae and Fagaceae. In the latter family, the biosynthetic modification of gallate is specially profound, leading up to seco-derivatives of the S (dehy-drochebuloyl) type.

Thus the distribution of gallic acid derivatives underlines the affinity of a large group of Hamamelidae. In the Urticales families, gallic acid and ellagic acid have been located (after hydrolysis of a crude extract) only in Ulmaceae and Barbeyaceae.

Phenolics (Table 9). Allylphenols and the neolignan magnolol were isolated from two of the more primitive families, the Myrothamnaceae and Cercidi-phyllaceae. The distribution of lignans is also surprisingly sparse and restricted to the Betulaceae, Fagaceae, Urticaceae, and Ulmaceae. Stilbenes and dihydrostilbenes occur in the Betulaceae, Fagaceae, and Moraceae, coumarins in the Myrothamnaceae, Betulaceae, Moraceae, and Ulmaceae, and xan-thones in the Betulaceae and Moraceae. Chemosys-tematically somewhat more useful clues are the dia-rylheptanoids of the Fagaceae, Juglandaceae, Myricaceae, and Casuarinaceae, while oligonaphtho-quinones are as characteristic of the Juglandaceae as the phoroglucinol and olivetol derivatives are of the Cannabaceae.

Terpenoids (Table 10). The terpenoids of the Hamamelidae are equally of rather ambiguous chemosystematic value. True, pentacyclic triterpenoids of the nor-oleanane type occur in the Trochodendraceae, Eupteleaceae, and Hamamelidaceae which, jointly with the Platanaceae (producing a nor-lupane type) all belong to the more primitive group. True, tetracyclic triterpenoids of the dammarane and the cyclo-artane types occur in the Betulaceae, Fagaceae, and Juglandaceae. Since, however, cycloartanes also have been reported for the Moraceae (and of course other angiosperm families), this is hardly of systematic relevance. This wealth of triterpenoids and even of some special steroids such as the brassinolides of the Hamamelidaceae and Fagaceae contrasts with the absence of diterpenoids, turning the triterpene/diter-pene ratio one of the most valuable (and astonishing) characteristic of the Hamamelidae.

A further evolutionary rule obeyed by angiosperm lineages concerns the replacement of compounds formed through the shikimate pathway by compounds formed through the acetate pathways (Table 11). This phenomenon may take place gradually, inducing initially the biosynthesis of compounds formed by both the shikimate and the acetate routes. Such is the case of the prenylphenolics of the Platanaceae, Myricaceae, and Moraceae. Chiefly the latter family is easily distinguished not only from other families of the Hamamelidae but from all plant families by the accumulation of an extraordinarily large number of structurally unusual prenylated fla-vonoids, xanthones, stilbenes, and coumarins. Total replacement of shikimate by acetate-derived metabolites is exemplified here by a comparison between the largely woody Moraceae, which synthesize prenylated shikimate derivatives, and the fully herbaceous Cannabaceae containing prenylated acetate deriva-

Table 10. Terpenoid types of Hamamelidae

Pentacyclic Tetracyclic Special Di- Sesqui- Mono-

Triterpenes triterpenes steroids terpenes terpenes terpenes

Table 10. Terpenoid types of Hamamelidae

Pentacyclic Tetracyclic Special Di- Sesqui- Mono-

Triterpenes triterpenes steroids terpenes terpenes terpenes

EUPT

Oil 012 Lui

TROC

OU 012 Lui

MYRO

CERC

RHOI

PLAT

Lui Lu3

HAMA

OU OB Url Lui

Br

+

+ Ir

BETU

OU Url Lui Frl Gl

Cyl Cy2 Cy3 La4

+

+

Tr Ts Hol

Dal Da2 Da3 Loi Lo2

FAGA

OU Url Lui Frl Gl

Cyl Cy2 Cy3 Br

+

+

Tr Ts Hol Ho2Ho3 Ar

Dal La2 La3

JUGL

Oll Url Lui

Cyl Cy2

+

+

MYRI

Oll Url Lui Tr

+

CASU

Oil Lui Tr

MORA

OU Url Lui Lu2 Frl

Cyl Eu Ti Ca

+

+

G1H02

CANN

+

+

CECR

OU Url Ur2

URTI

OU Url Lui

+

ULMA

OU Lui Frl Hol Ho2 Ho3

+

+

BARB

Table 11. Biosynthetic pathways leading to classes of secondary metabolites of chemosystematic potential

- Polyketides -

Mevalonic acid -

Carbohydrates

  • Krebs cycle -
  • Polyacetylenes r Iridoids Sesquiterpene lactones Diterpenoids Triterpenoids Steroids
  • Quinolizidine alkaloids Pyrrolizidinc alkaloids Tropane alkaloids

Shikimic acid

Chorismic ' acid

Phenylalanine

Cinnamic _ acids

Cinnamyl alcohols

Propenylphenols Allylphenols

Gallic acid

Anthra-nilic acid

Indole alkaloids,

Benzyliso-quinoline alkaloids

Betalains

Flavonoids

Proantho-cyanidins

Lignans Lignins

Neolignans tives. Krebs cycle and hence acetate-derived alkaloids occur in the Moraceae (indolizidines, qui-nolines, bipyridines), Urticaceae (quinolizidines), and Ulmaceae (pyridines), three families belonging to the gallate-free or gallate-poor group.

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