Handbook of Herbs and Spices - Volume 3

Volatiles from herbs and spices 181

IPP to GPP through the mediation of a further synthase enzyme, resulting in the

production of the first 15-carbon unit, farnesyl pyrophosphate (FPP).

11.3.2 Biosynthesis of phenylpropenes

Shikimic acid is formed from glucose in plants, and is the biogenic precursor of the

amino acids L-phenylalanine, L-tyrosine and L-tryptophan. Pathways from shikimic

acid generate anthranilates (e.g. in mandarin oil Citrus reticulata), cinnamates (e.g.

in Peru balsam oil Myroxylon pereirae) and other phenylpropanoids, and from this

point on to other metabolites such as lignans and flavononoids. In particular, phenyl

propanoids (basically compounds with a 3-carbon chain attached to a benzene ring)

are formed from trans or (E)-cinnamic acid via the elimination of ammonia from L-

phenylalanine. Common phenylpropanoids in essential oils include methyl chavicol,

methyl eugenol, eugenol, methyl cinnamate, vanillin and anethole. The shikimic acid

pathway produces the amino acid phenylalanine which by the action of phenyl alanine

ammonia lyase is converted to trans-cinnamic acid (Bramley 1997, Waterman 1993).

Fig. 11.4 (a) Conversion of mevalonate into activated isoprene units (Source: Nelson and Cox

(2001)); (b) formation of GPP and FPP from DMAPP (Source: Nelson and Cox (2001)); (c)

formation of monoterpenes from GPP (Source: Waterman (1993)); (d) formation of

sesquiterpenes from EPP (Source: Waterman (1993)).

IPP = Isopentenyl pyrophosphate

(a)

3

–IPP

Mevalonate

OOC CH 2 C CH 2 CH 2 OH

OH

CH 3

+3ATP

–3ADP

OOC CH 2 C CH 2 CH 2 O

CH 3

P O P O

O

O

O

O

O P O

O

O

• CO 2


• PO 4 2–

3-phospho-5-pyrophospho mevalonate

CH 2 C CH 2 CH 2 O P O P

CH 3

O

O O

O O

CH 3 C CH CH 2 O P O P

CH 3

O

O O

O O

DMAPP = Dimethyl allyl pyrophosphate