Decarboxylations are pervasive in biology. They are often classified according to the cofactors that catalyze the transformations.
Biotin-coupled processes effect the decarboxylation of
malonyl-CoA to
acetyl-CoA.
Thiamine (T:) is the active component for decarboxylation of
alpha-ketoacids, including pyruvate: : :
Pyridoxal phosphate promotes decarboxylation of amino acids.
Flavin-dependent decarboxylases are involved in transformations of cysteine. Iron-based hydroxylases operate by reductive activation of using the decarboxylation of
alpha-ketoglutarate as an electron donor. The decarboxylation can be depicted as such: :{{chem2|RC(O)CO2Fe O2 -> RCO2Fe{IV}\dO + CO2}} :
Decarboxylation of amino acids Common
biosynthetic oxidative decarboxylations of
amino acids to
amines are: •
tryptophan to
tryptamine •
phenylalanine to
phenylethylamine •
tyrosine to
tyramine •
histidine to
histamine •
serine to
ethanolamine •
glutamic acid to
GABA •
lysine to
cadaverine •
arginine to
agmatine •
ornithine to
putrescine •
5-HTP to
serotonin •
L-DOPA to
dopamine Other decarboxylation reactions from the
citric acid cycle include: •
pyruvate to
acetyl-CoA (see
pyruvate decarboxylation) •
oxalosuccinate to α-
ketoglutarate • α-
ketoglutarate to
succinyl-CoA.
Fatty acid synthesis Straight-chain fatty acid synthesis occurs by recurring reactions involving decarboxylation of
malonyl-CoA. ==Case studies== when consumed and depends on conversion of the
enol to a keto group when the alpha carbon is protonated. Upon heating, Δ9-tetrahydrocannabinolic acid decarboxylates to give the psychoactive compound Δ9-
Tetrahydrocannabinol. When cannabis is heated in vacuum, the decarboxylation of
tetrahydrocannabinolic acid (THCA) appears to follow
first order kinetics. The log fraction of THCA present decreases steadily over time, and the rate of decrease varies according to temperature. At 10-degree increments from 100 to 140 °C, half of the THCA is consumed in 30, 11, 6, 3, and 2 minutes; hence the rate constant follows
Arrhenius' law, ranging between 10−8 and 10−5 in a linear log-log relationship with inverse temperature. However, modelling of decarboxylation of
salicylic acid with a water molecule had suggested an activation barrier of 150 kJ/mol for a single molecule in solvent, much too high for the observed rate. Therefore, it was concluded that this reaction, conducted in the solid phase in plant material with a high fraction of carboxylic acids, follows a pseudo first order kinetics in which a nearby carboxylic acid precipitates without affecting the observed rate constant. Two transition states corresponding to indirect and direct keto-enol routes are possible, with energies of 93 and 104 kJ/mol. Both intermediates involve protonation of the
alpha carbon, disrupting one of the double bonds of the aromatic ring and permitting the beta-keto group (which takes the form of an
enol in THCA and THC) to participate in decarboxylation. In beverages stored for long periods, very small amounts of
benzene may form from
benzoic acid by decarboxylation catalyzed by the presence of
ascorbic acid. The addition of catalytic amounts of
cyclohexenone has been reported to catalyze the decarboxylation of
amino acids. However, using such catalysts may also yield an amount of unwanted by-products. ==References==