PSE 406: Lecture 15 1

Wood ChemistryPSE 406

Lecture 15Stilbenes, Flavonoids, Condensed and

Hydrolysable Tannins, other Miscellaneous Extractives and

Inorganic Compounds

PSE 406: Lecture 15 2

Stilbenes Phenolic extractive found in the heartwood of

softwoods» Particularly prevalent in Pinus

Most often 2 aromatic rings: occasionally more Presence of double bond linkage

» Naturally present most often in trans form

CH CH

HO

4-Hydroxystilbene

CH CH

OH

HO

Pinosylvin

CH CHHO

Glu O

Piceid

PSE 406: Lecture 15 3

Flavonoids

Serve many roles in plants:» Protection» Coloration» Other unique roles.

(Western Hemlock)

O

OH

OH

OH

OH

HO

Catechin

PSE 406: Lecture 15 4

FlavonoidsGeneral Structural

Information

Polyphenolic compounds found in softwoods and hardwoods

Composed of diphenylpropane units C6-C3-C6

Eight structural classifications Flavonoids differ through

substitution on the rings» Typically OH or OCH3 groups» Typical to have OH on positions:

– 5 and 7– 3’, 4’ and 5’

Are also present as gylcosides

O

A

B

C2

3

456

7

8

2'3'

4'

5'6'

PSE 406: Lecture 15 5

Representative Structures of Flavonoid Classes

O

OOH

HO

Chrysin

O

OH O

OH

OH

OH

HO

Taxifolin

O

OOH

HO

Pinocembrin

O

O

OH

OH

HO

Pinobanskin

O

OH O

OH

OH

OH

HO

Quercitin

O

OH

OH

OH

OH

HO

Catechin

(Douglas Fir)

(Western Hemlock) (Oak)

PSE 406: Lecture 15 6

FlavonoidsBiological Significance

Not all flavonoids have same function in plants

Anti-fungal Antioxidant Color: bright colors in plants

PSE 406: Lecture 15 7

FlavonoidsLocation in Tree

Found in the heartwood of most tress» Often responsible for coloration

Found in lesser amounts in the sapwood Are found in large amounts in bark and

roots Leaves: green tea can contain up to 30%

flavonoids Flowers: color is often due to flavonoids

PSE 406: Lecture 15 8

FlavonoidsMedicinal Uses

Higher flavonoid content in diet reduces chance of:» Heart Disease

– Strengthen capillaries– Dilates blood vessels

» Stroke» Cancer: all types reduced

– Finnish study = ½ rate of cancer

PSE 406: Lecture 15 9

Condensed Tannins

Condensed tannins are formed through the polymerization of flavan-3-ol (catechin) and flavan–3,4-diols (leucoanthocyanidins)» 2-50 units

– Typically 2-8

» Linkages can be through a variety of sites

O

OH

OH

Flavan-3,4-diols(Leucoanthocyanidins)

O

OH

Flavan-3-ols(Catechins)

PSE 406: Lecture 15 10

Condensed Tannins

Typical Structure of Condensed Tannins

O

OH

O OH

OH

OH

OH

OH

OOH

OH

OH

HO HO

HO

HO

O

OH

OH

Leucoanthocyanidins (flavan-3,4-diols)

O

OH

Catechins(flavan-3-ols)

PSE 406: Lecture 15 11

Condensed TanninsLocation in the Tree

Western hemlock» Bark: 18% tannins» Wood: 2% tannins

PSE 406: Lecture 15 12

Condensed TanninsBiological Significance

Protection of plants against insects/animals» Bad Taste (bitter taste)

Toxic to bacteria Pine calluses: created by fungal invasion

» Tree forms calluses as protective tissue» Calluses contain high levels of tannins

Uses of condensed tannins» Leather tanning: 10,000+ year old industry» Adhesives

PSE 406: Lecture 15 13

Hydrolyzable TanninsStructure

Polymers (esters) of a sugar (usually glucose) with one or more polyphenolic carboxylic acids.

Gallotannins: Gallic acid polymer Ellagitannins: Ellagic Acid polymer

COOH

OH

OHHO

Gallic Acid

OH

OH

CO

OH

OHC

HO

O

HOO

Digallic Acid

OH

C

O

OH

OH

O

C

HO

O

O

Ellagic Acid

PSE 406: Lecture 15 14

Hydrolyzable TanninsPolymer Structure Example

O

O

O

OH

O

O

HO

HO

OH

O

HO

HO

O

OH

OHO

OH

OH

OH

O

OH

OH

OH

O

O

OH

OH

O

O n

Sugar

PSE 406: Lecture 15 15

Hydrolyzable TanninsGeneral Information

Rare to nonexistent in softwoods. Hardwoods which contain large amounts:

» Oak (gallic and ellagic tannins)» Eucalyptus (Ellagitannins)» Chestnut (gallic tannins)

Hydrolyzable tannins located in heartwood. Pulp and paper problems:

» Increased consumption of bleaching chemicals.» Coloration problems.

PSE 406: Lecture 15 16

Tetraterpenes

Polymers of isoprene containing 40 carbons (8 isoprene units)

Most common are the carotenoids» Generally derivatives of lycopene

– This is a carontenoid which is in high concentration in red fruits (gives color): tomatoes, watermelon, guava, etc.

PSE 406: Lecture 15 17

Carotene

Tetraterpene carotenoid found in dark green and orange yellow vegetables.

In the human body, it is converted to vitamin A Has been shown to be have many health

related benefits.

PSE 406: Lecture 15 18

Alkaloids (1) These nitrogen containing

compounds are found in a variety of different plants.» Located in the leaves, fruits, and bark.

Quinine» Used to treat malaria» Isolated from bark of cinchonas (South

American Hardwood) – some eucalyptus species

» Causes pulping problems Strychnine

» Found in seeds of tree Strychnos nux-vomica (Tropical hardwood)

N

NCH3

O O

+OH-

Strychnine

N

N

CH2

HO

H3CO

Quinine

PSE 406: Lecture 15 19

Alkaloids (2)

You are all aware of the alkaloids shown on this page you probably have never seen their structures. These are typically found in small amounts in plants but are worth large sums of cash.

NO

O

N

N

N

N

O

O

N

O

O

Nicotine Caffeine

Cocaine

PSE 406: Lecture 15 20

Inorganic Materials

Inorganic materials » Plants contains small amounts of most metals.

– Some are used by living cells– Some present as contaminants

Ash content gives a rough idea of the amounts of metals present.» Sugar cane: 1.7-3.8% ash» Corn Cobs: 2% ash

Temperate woods contain 0.1-1% ash while tropical and subtropical species contain up to 5% ash.» Main components Ca (50%), potassium and

magnesium.

PSE 406: Lecture 15 21

Inorganics in Grasses

Grasses contain high levels of inorganics particularly silica.

Wheat straw: Reported values 4-12+% ash» Leaves: 14-19% ash, 10-14% silica» Nodes: 8-14% ash, 5-7% silica» Internodes: 3+% ash, 2+% silica