Furthermore, a significant proportion of essential cofactors (or cosubstrates) for
other enzyme-catalyzed reactions involve phosphate esters. Adenosine triphosphate
(ATP) represents the phosphate donor for most biological phosphorylation reactions and hence constitutes the universal ‘energy-currency’ in biological systems.
For many redox-reactions, nicotinamide adenine dinucleotide phosphate (NADP
+
)
or glucose-6-phosphate (G6P) are an essential cofactor or cosubstrate (Sect. 2.2.1).
Dihydroxyacetone phosphate (DHAP) is an important activated cosubstrate for
enzymatic aldol reactions (Sect. 2.4.1), thiamine diphosphate (TDP) is an essential
cofactor for enzymatic acyloin and benzoin condensations (Sect. 2.4.2) and pyridoxal-5
0 -phosphate (PLP) serves as molecular shuttle for transamination reactions
(Sect. 2.6.2). Glycosyl phosphates are essential for glycosyl transfer reactions
catalyzed by carbohydrate phosphorylases (Sect. 2.6.1). In addition, the emerging
field of metabolic engineering creates a substantial market for phosphorylated
metabolites [544].
Hydrolysis of Phosphate Esters
Chemoselective Hydrolysis of Phosphate Esters Chemical hydrolysis of
polyprenyl pyrophosphates is hampered by side reactions due to the lability of the
molecule. Hydrolysis catalyzed by acid phosphatase – an enzyme named because it
displays its pH-optimum in the acidic range – readily afforded the corresponding
dephosphorylated products in acceptable yields [545].
The product from a DHAP-depending aldolase-reaction is a sensitive
2-oxo-1,3,4-triol, which is phosphorylated at position 1 (Scheme 2.72). Mild
dephosphorylation by using acid phosphatase without cumbersome isolation of
the polar phosphorylated intermediate is a standard method to obtain the chiral
polyol product [546–549] in good yield. In the latter example, it was transformed
into the sex pheromone of the pine bark beetle (+)-exo-brevicomin.
Enantioselective Hydrolysis of Phosphate Esters In comparison with the
hydrolysis of carboxyl esters, enantioselective hydrolyses of phosphate esters
have been seldom reported due to problems to handle charged species. Acid
phosphatases were applied to the kinetic resolution of serine and threonine via
hydrolysis of the corresponding O-phosphate esters (Scheme 2.73) [550]. As for
the resolutions of amino acid derivatives using proteases, the natural L-enantiomer was hydrolyzed in the case of threonine O-phosphate, leaving the D-counterpart behind (E > 200). After separation of the D-phosphate from L-threonine,
the D-enantiomer could be dephosphorylated using an unspecific alkaline phosphatase – an enzyme with the name derived from having its pH-optimum in the
alkaline region. Interestingly, the N151D mutant exhibited an opposite
enantiopreference for the D-enantiomer in case of DL-serine-O-phosphate
(E ¼ 18) [551].
2.1 Hydrolytic Reactions
105
other enzyme-catalyzed reactions involve phosphate esters. Adenosine triphosphate
(ATP) represents the phosphate donor for most biological phosphorylation reactions and hence constitutes the universal ‘energy-currency’ in biological systems.
For many redox-reactions, nicotinamide adenine dinucleotide phosphate (NADP
+
)
or glucose-6-phosphate (G6P) are an essential cofactor or cosubstrate (Sect. 2.2.1).
Dihydroxyacetone phosphate (DHAP) is an important activated cosubstrate for
enzymatic aldol reactions (Sect. 2.4.1), thiamine diphosphate (TDP) is an essential
cofactor for enzymatic acyloin and benzoin condensations (Sect. 2.4.2) and pyridoxal-5
0 -phosphate (PLP) serves as molecular shuttle for transamination reactions
(Sect. 2.6.2). Glycosyl phosphates are essential for glycosyl transfer reactions
catalyzed by carbohydrate phosphorylases (Sect. 2.6.1). In addition, the emerging
field of metabolic engineering creates a substantial market for phosphorylated
metabolites [544].
Hydrolysis of Phosphate Esters
Chemoselective Hydrolysis of Phosphate Esters Chemical hydrolysis of
polyprenyl pyrophosphates is hampered by side reactions due to the lability of the
molecule. Hydrolysis catalyzed by acid phosphatase – an enzyme named because it
displays its pH-optimum in the acidic range – readily afforded the corresponding
dephosphorylated products in acceptable yields [545].
The product from a DHAP-depending aldolase-reaction is a sensitive
2-oxo-1,3,4-triol, which is phosphorylated at position 1 (Scheme 2.72). Mild
dephosphorylation by using acid phosphatase without cumbersome isolation of
the polar phosphorylated intermediate is a standard method to obtain the chiral
polyol product [546–549] in good yield. In the latter example, it was transformed
into the sex pheromone of the pine bark beetle (+)-exo-brevicomin.
Enantioselective Hydrolysis of Phosphate Esters In comparison with the
hydrolysis of carboxyl esters, enantioselective hydrolyses of phosphate esters
have been seldom reported due to problems to handle charged species. Acid
phosphatases were applied to the kinetic resolution of serine and threonine via
hydrolysis of the corresponding O-phosphate esters (Scheme 2.73) [550]. As for
the resolutions of amino acid derivatives using proteases, the natural L-enantiomer was hydrolyzed in the case of threonine O-phosphate, leaving the D-counterpart behind (E > 200). After separation of the D-phosphate from L-threonine,
the D-enantiomer could be dephosphorylated using an unspecific alkaline phosphatase – an enzyme with the name derived from having its pH-optimum in the
alkaline region. Interestingly, the N151D mutant exhibited an opposite
enantiopreference for the D-enantiomer in case of DL-serine-O-phosphate
(E ¼ 18) [551].
2.1 Hydrolytic Reactions
105