Part F | 30.2
732 Part F Marine Derived Metabolites
metabolic function and strictly related to the natural
source and environment.
In comparison with chemical glycosylation, including methods that are generally based on harsh conditions
or necessitate toxic (heavy metals) catalysts, enzymatic
routes are particularly useful for accessing new products
or for the modification of complex natural products such
as carbohydrates [30.1]. Actually, enzymes may represent an imperative choice in fields related to the food
domain or cosmetics in which adopting synthetic chemistry is sometimes not acceptable at all.
As sources of biocatalysts alternative to microorganisms, like plants or animals, almonds and pig and
horse livers furnished few but relevant examples [30.2].
Carbohydrates are important molecules in various technological domains. In the field of polymer chemistry,
for example, synthetic carbohydrate-containing polymers have a wide range of applications in medical
biotechnology as coating agents or molecular recognition biomedical materials. Molecular networks presenting as hydrogels may find application as biomaterials
because of their high water content, homogeneity, stability, and expected nontoxicity [30.3]. In food technology, during the last decade, a number of novel dietary
carbohydrates produced by enzymatic synthesis have
been introduced [30.4]. Resulting from advances in
fine chemicals production, the easy synthesis of chromophoric oligosaccharides (such as nitrophenyl and
4-methylumbelliferyl glycosides and others) of defined
structure is of widespread interest because these products are valuable tools for the kinetic analysis of hydrolytic activities and for characterization of the action
of new enzymes (i. e., exo or endoglycosidases). Finally, in cosmetics the prodrug action of enzymatically
glycosylated natural lipophilic antioxidants is nowadays often considered. Thus, glycosylation is considered to be an important method for the structural modification of compounds with useful biological activities.
It allows conversion of lipophilic compounds into hydrophilic ones, improving pharmacokinetic properties
and producing more effective drug delivery systems
(prodrugs) [30.5].
The marine ecosystem is an almost absolutely
new and unexplored source of biological material and
can be also a surprising source of enzymes carrying
new and interesting catalytic activities to be applied
in biocatalysis [30.6]. Marine sources are represented
by marine microorganisms, including extremophiles
and marine plants or animals. Marine microorganisms may be used for industrial production of many
enzymes [30.7]; moreover, although not numerous, examples of different enzymes from marine plants and
animals are also reported in the literature [30.8]. Marine enzymes are characterized by well-known habitatrelated features such as salt tolerance, hyperthermostability, barophilicity, and cold adaptivity . In addition,
their novel chemical and stereochemical characteristics have increased the interest of biocatalysis practitioners from academia and research. Marine (micro)organisms should be considered as an important
source of biocatalysts for the degradation of complex
polysaccharides. Herbivorous marine molluscs such as
abalone, sea hares, and small snails possessing various kinds of polysaccharide-degrading enzymes could
efficiently depolymerize alginate, mannan, laminarin,
and cellulose. These enzymes play important roles in
the metabolism of the organism digesting polymeric
materials to oligosaccharides and monosaccharides as
carbohydrate nutrients. However, these molecules (poly
and oligosaccharides) are known to exhibit various therapeutical functions and are recognized as potential raw
materials for biofuels [30.9].
Different interesting results related to the presence
of glycosyl hydrolases have been reported for Aplysia
fasciata and Aplysia kurodai in the last decade. Both
species have been revealed to be potent producers of
a library of glycoside hydrolases applied in the synthesis and hydrolysis of glycosidic bonds. In this chapter,
examples of applications of such enzymes will be
discussed.
30.2 Biocatalytic Methodologies to Access Glycosides
and Oligosaccharides
30.2.1 Enzymes
Nowadays there exists a copious amount of information
concerning the synthesis and transformation of complex
saccharides in living organisms. Glycosidic linkage is
by far the most common chemical bond joining a carbohydrate to another molecule. It is one the most important chemical characteristic of a saccharide, although
diverse functional groups can be found in carbohydrate
chains (ester, sulphate, etc.) in various positions, which
732 Part F Marine Derived Metabolites
metabolic function and strictly related to the natural
source and environment.
In comparison with chemical glycosylation, including methods that are generally based on harsh conditions
or necessitate toxic (heavy metals) catalysts, enzymatic
routes are particularly useful for accessing new products
or for the modification of complex natural products such
as carbohydrates [30.1]. Actually, enzymes may represent an imperative choice in fields related to the food
domain or cosmetics in which adopting synthetic chemistry is sometimes not acceptable at all.
As sources of biocatalysts alternative to microorganisms, like plants or animals, almonds and pig and
horse livers furnished few but relevant examples [30.2].
Carbohydrates are important molecules in various technological domains. In the field of polymer chemistry,
for example, synthetic carbohydrate-containing polymers have a wide range of applications in medical
biotechnology as coating agents or molecular recognition biomedical materials. Molecular networks presenting as hydrogels may find application as biomaterials
because of their high water content, homogeneity, stability, and expected nontoxicity [30.3]. In food technology, during the last decade, a number of novel dietary
carbohydrates produced by enzymatic synthesis have
been introduced [30.4]. Resulting from advances in
fine chemicals production, the easy synthesis of chromophoric oligosaccharides (such as nitrophenyl and
4-methylumbelliferyl glycosides and others) of defined
structure is of widespread interest because these products are valuable tools for the kinetic analysis of hydrolytic activities and for characterization of the action
of new enzymes (i. e., exo or endoglycosidases). Finally, in cosmetics the prodrug action of enzymatically
glycosylated natural lipophilic antioxidants is nowadays often considered. Thus, glycosylation is considered to be an important method for the structural modification of compounds with useful biological activities.
It allows conversion of lipophilic compounds into hydrophilic ones, improving pharmacokinetic properties
and producing more effective drug delivery systems
(prodrugs) [30.5].
The marine ecosystem is an almost absolutely
new and unexplored source of biological material and
can be also a surprising source of enzymes carrying
new and interesting catalytic activities to be applied
in biocatalysis [30.6]. Marine sources are represented
by marine microorganisms, including extremophiles
and marine plants or animals. Marine microorganisms may be used for industrial production of many
enzymes [30.7]; moreover, although not numerous, examples of different enzymes from marine plants and
animals are also reported in the literature [30.8]. Marine enzymes are characterized by well-known habitatrelated features such as salt tolerance, hyperthermostability, barophilicity, and cold adaptivity . In addition,
their novel chemical and stereochemical characteristics have increased the interest of biocatalysis practitioners from academia and research. Marine (micro)organisms should be considered as an important
source of biocatalysts for the degradation of complex
polysaccharides. Herbivorous marine molluscs such as
abalone, sea hares, and small snails possessing various kinds of polysaccharide-degrading enzymes could
efficiently depolymerize alginate, mannan, laminarin,
and cellulose. These enzymes play important roles in
the metabolism of the organism digesting polymeric
materials to oligosaccharides and monosaccharides as
carbohydrate nutrients. However, these molecules (poly
and oligosaccharides) are known to exhibit various therapeutical functions and are recognized as potential raw
materials for biofuels [30.9].
Different interesting results related to the presence
of glycosyl hydrolases have been reported for Aplysia
fasciata and Aplysia kurodai in the last decade. Both
species have been revealed to be potent producers of
a library of glycoside hydrolases applied in the synthesis and hydrolysis of glycosidic bonds. In this chapter,
examples of applications of such enzymes will be
discussed.
30.2 Biocatalytic Methodologies to Access Glycosides
and Oligosaccharides
30.2.1 Enzymes
Nowadays there exists a copious amount of information
concerning the synthesis and transformation of complex
saccharides in living organisms. Glycosidic linkage is
by far the most common chemical bond joining a carbohydrate to another molecule. It is one the most important chemical characteristic of a saccharide, although
diverse functional groups can be found in carbohydrate
chains (ester, sulphate, etc.) in various positions, which