Phenylpropanoids, Lignans and Lignin
C6-C3 metabolism, also C6-C1 metabolism
C6-C2 compounds are sometimes formed by α-
oxidation, but are uncommon
cinnamic acid and p-coumaric acids are ubiquitous in plants
they are precursors to many other groups of phenylpropanoid acids
PAL (TAL) mostly in the cytoplasm
the reactions that these enzymes catalyze are reversible
Almost all phenylpropanoids are derived from cinnamic acid via p-coumaric acid
E-cinnamic acid ----> O2, NADPH ----> p-coumaric acid
OXIDATION OF PHENYLPROPANOIDS
oxidation steps ...
p-coumaric acid ----> caffeic acid ----> ferulic acid ----> sinapic acid
but these steps occur as the quinate and shikimate esters, they require NADPH and O2
esters of these acids are commonplace in plants, e.g., chlorogenic acid (caffeic acid and quinic acid)
ALLELOPATHY
many of these compounds are allelopathic, that is, they inhibit growth of competing plantsVOLATILE PHENYLPROPANOIDS
These compounds are frequent components of essential oils. They are usually isolated by steam distillation.
In the first step, p-coumaric acid ----> cinnamyl alcohols
the reaction also goes through the aldehyde stage, and there is elimination of a phosphate group
biosynthesis of compounds such as safrole and eugenol
formation of these compounds involves relatively specific methyltransferase reactions. Compounds
with methylenedioxy groups (such as safrole) are derived from methyl ethers. Label is introduced
into all of these from SAM.
Allyl and propenyl isomers co-occur. Normally, the allyl isomers are formed and are isomerized
during isolation or subsequent processing.
essential oil components are important in spices.
phenylpropanoids in black pepper and chiles (piperine and capsaicin, respectively),
are the pungent compounds
compounds with methylenedioxy groups (e.g., safrole, isosafrole) are mixed function oxidase inhibitors,
and are often synergistic in activity of other compounds because they block degradation of other
metabolites in the animals. Piperonal is a useful synergist for insecticidal mixtures.
piperonyl butoxide is a similar, synthetic synergist for activation of insecticides
Myristicin and elemicin have hallucinogenic properties. Both are found in nutmeg
methyl eugenol is a powerful attractant for oriental fruit flies (oriental), but is not a sexual
pheromone
many phenylpropanoids are involved in plant-insect interactions
LIGNANS
about 450 lignans known, in at least 55 plant families
four major subtypes known
optically active
precursors closely related to those of lignin biosynthesis, but these compounds are usually optically
active and are derived from enzymatically controlled highly-specific biosynthetic processes
NADH, H2O2, plus enzyme ----> lignans
sesamin - from sesame seed oil, synergist for insecticides; also used as an oil for pharmacological testing
NDGA - once widely used as a food additive, several have anti-tumor (anti-viral) activity
podophyllotoxin - antimitotic activity; chemically modified derivatives of podophyllotoxin are current used for tumor treatment
LIGNINafter cellulose, these are the most abundant/most widely distributed natural product in plants land plants - not in algae or bryophytes
lignin is a major component of cell walls - and conducting elements for water transport
polymeric (monolignols) corresponding alcohols are derived from the corresponding acids. They may be stored as glycosides
lignins of conifers/softwoods are based mostly on coniferyl alcohol
lignins of hardwoods are mostly based on coniferyl and sinapyl alcohols
lignins of bamboo/grasses, palms mostly are based on p-coumaryl alcohol
recent biosynthetic work done by Dr. Normal Lewis group at Washington State University. They found that perhaps 5 or 6 peroxidase enzymes are important in lignin formation
in addition, another group of specific protein molecules that seem to hold the precursors in place. They called these "dirigent" proteins. In the cells where lignin is formed, the precursors are transported to the far end of the cell and polymerized in specific cell layers and in specific order. The dirigent proteins, oxidases, and monomers are all required for this to happen. The gene sequence of these dirigent proteins is unlike any other enzymes yet known. The system is quite specific, (+)-pinoresinol is made from (E)-coniferyl alcohol.
C6-C1 compounds
β-oxidation of C6-C3 compounds is a major route (but many others come from polyketide or from shikimic acid pathways)
C6-C1 compounds are also found in many essential oils, spices, e.g., anisaldehyde, methyl salicylate
BIOACTIVITY OF C6-C3 COMPOUNDS
K-PLMF1 Compounds of this type (turgorins) in Mimosa are involved in leaf closures
acetosyringone, a (vir)gene activator for Agrobacterium tumefaciens
Survey of phenylpropanoid biosynthesis
Biosynthesis of Phenylpropanoids
Phenylacetic acid and homogentisic acid
Biogenesis of volatile phenylpropanoids
Assorted volatile phenylpropanoids
Syringin and coniferin biosynthesis
Dehydrodiconiferyl alcohol β-D-glycosides
Euglossine bees attracted by phenylpropanoids
Lecture Slides
© David S. Seigler, Integrative Biology 425, Plant Secondary Metabolism, Department of Plant
Biology, 265 Morrill Hall, 505 S. Goodwin Ave., University of Illinois, Urbana, Illinois 61801, USA.
217-333-7577. seigler@life.uiuc.edu.
