neutralophiles, alkaliphiles are the most promising sources of alkaline active proteases. Moreover, alkaliphiles often exhibit halophilicity, and their enzymes tend to
show relatively better activity in low water activity than their non-alkaliphilic
counterparts. Thus, proteases from alkaliphiles are expected to be more effective
in nonaqueous medium and are more interesting for peptide synthesis.
Alkaline active proteases are also used in synthesis of other compounds. Synthesis of 2H-1-benzopyran-2-one and polymerizable vinyl guaifenesin ester has been
demonstrated using the alkaline active proteases from Bacillus licheniformis [136]
and Bacillus subtilis [137], respectively. Other alkaline active enzymes used in
synthesis of valuable substances are cyclo-maltodextrin glucanotransferases
(CGTases) which are capable of producing cyclodextrins (CDs), substances widely
applied in pharmaceutical, food, and chemical industries [138, 139]. In 2019, several
tons of cyclodextrins with an estimated global sell of US $180 million have been
produced by enzymatic conversion using alkaline active CGTases of alkaliphiles
[140]. Alkaline active CGTases are covered in this volume [141].
Lipases and esterases have also been considered in catalyzing synthesis reactions.
For instance, the alkaline active lipase from haloalkalophilic Bacillus atrophaeus
FSHM2 is used to synthesize ethyl valerate and methyl valerate [142], and the
alkaline active esterase is applied to make racemic resolution of O-benzyl lactic
acid ethyl ester, an intermediate in the production of the third-generation widespectrum antibiotic, levofloxacin [143]. In a similar way, an alkaline active epoxide
hydrolase of Maritimibacter alkaliphilus was used to obtain enantiopure (R)glycidyl phenyl ether by selectively hydrolyzing the (S)-glycidyl phenyl ether in
the racemic mixture to diol. Thus, this alkaliphilic enzyme can be used in production
of enantiopure epoxides and diols [144]. An alkaline active esterase from
Pelagibacterium halotolerans converts dimethyl 3-(4-fluorophenyl)glutarate
(3-DFG) into methyl (R)-3-(4-fluorophenyl)glutarate ((R)-3MFG), precursor for
the synthesis of the antidepressant paroxetine hydrochloride [145]. Some of these
reactions mediated by alkaline active enzymes are shown in Fig. 4.
It is not only isolated enzymes which have been considered for synthesis, whole
alkaliphile cells have been used to make a wide range of chemicals. Here are some
examples. The alkaliphilic strains of Alkalibacterium iburiense, Alkalibacterium
psychrotolerans, and Bacillus spp. [146–149], which play pivotal role in the production of indigo dye, can be mentioned as examples. In the dye making vat, a
number of oxidation and reduction reactions occur in sequential steps, and the
alkaliphilic microbes play the crucial reduction role [150]. Another example could
be the biotransformation of ferulic acid to vanillin using an alkaliphilic
Bacillus [151].
20
G. Mamo and B. Mattiasson
show relatively better activity in low water activity than their non-alkaliphilic
counterparts. Thus, proteases from alkaliphiles are expected to be more effective
in nonaqueous medium and are more interesting for peptide synthesis.
Alkaline active proteases are also used in synthesis of other compounds. Synthesis of 2H-1-benzopyran-2-one and polymerizable vinyl guaifenesin ester has been
demonstrated using the alkaline active proteases from Bacillus licheniformis [136]
and Bacillus subtilis [137], respectively. Other alkaline active enzymes used in
synthesis of valuable substances are cyclo-maltodextrin glucanotransferases
(CGTases) which are capable of producing cyclodextrins (CDs), substances widely
applied in pharmaceutical, food, and chemical industries [138, 139]. In 2019, several
tons of cyclodextrins with an estimated global sell of US $180 million have been
produced by enzymatic conversion using alkaline active CGTases of alkaliphiles
[140]. Alkaline active CGTases are covered in this volume [141].
Lipases and esterases have also been considered in catalyzing synthesis reactions.
For instance, the alkaline active lipase from haloalkalophilic Bacillus atrophaeus
FSHM2 is used to synthesize ethyl valerate and methyl valerate [142], and the
alkaline active esterase is applied to make racemic resolution of O-benzyl lactic
acid ethyl ester, an intermediate in the production of the third-generation widespectrum antibiotic, levofloxacin [143]. In a similar way, an alkaline active epoxide
hydrolase of Maritimibacter alkaliphilus was used to obtain enantiopure (R)glycidyl phenyl ether by selectively hydrolyzing the (S)-glycidyl phenyl ether in
the racemic mixture to diol. Thus, this alkaliphilic enzyme can be used in production
of enantiopure epoxides and diols [144]. An alkaline active esterase from
Pelagibacterium halotolerans converts dimethyl 3-(4-fluorophenyl)glutarate
(3-DFG) into methyl (R)-3-(4-fluorophenyl)glutarate ((R)-3MFG), precursor for
the synthesis of the antidepressant paroxetine hydrochloride [145]. Some of these
reactions mediated by alkaline active enzymes are shown in Fig. 4.
It is not only isolated enzymes which have been considered for synthesis, whole
alkaliphile cells have been used to make a wide range of chemicals. Here are some
examples. The alkaliphilic strains of Alkalibacterium iburiense, Alkalibacterium
psychrotolerans, and Bacillus spp. [146–149], which play pivotal role in the production of indigo dye, can be mentioned as examples. In the dye making vat, a
number of oxidation and reduction reactions occur in sequential steps, and the
alkaliphilic microbes play the crucial reduction role [150]. Another example could
be the biotransformation of ferulic acid to vanillin using an alkaliphilic
Bacillus [151].
20
G. Mamo and B. Mattiasson