14
1.3.2 Native Cyclodextrins
Schardinger recognized only dextrin-α and dextrin-β, while Freudenberg obtained
γ-dextrin in 1948, although previously regarded by him as a cyclic heptasaccharide
(Freudenberg and Cramer 1948). Two years later, Freudenberg elucidated the structure of γ-dextrin (Freudenberg and Cramer 1950). The same year, using partial acid
hydrolysis and enzyme digestion followed by X-ray measurements and paper chromatography, French also elucidated the structure of γ-dextrin, first named cycloöctaamylose and later cyclooctaamylose (French et al. 1950b). This dextrin was
composed of eight glucose residues symmetrically arranged in a ring and linked
together by α-1,4-glucosidic bonds. In the late 1950s, French and co-workers had
established the molecular weight, the exact chemical structure, the dimensions, and
the types of bonding in the three cycloamyloses, cyclohexaamylose, cycloheptaamylose, and cyclooctaamylose, i.e., α-dextrin, β-dextrin, and γ-dextrin, respectively (French and McIntire 1950; Norberg and French 1950; French et al. 1950a, b).
In 1948, the first indications of the existence of higher homologues of dextrins
were published by Freudenberg and his young student Cramer (Freudenberg and
Cramer 1948). Two years later, French also suggested the possible existence of
cycloamyloses containing more than 8 glycosyl units (Norberg and French 1950;
French et al. 1950b). The same year, Akiya and co-workers claimed the “discovery
of new series of cyclic oligosaccharides” similar to the Schardinger dextrins, containing more than 8 glucose units (Akiya and Watanabe 1950a, b, c; Akiya and Okui
1951). Later, Caesar (1968) reported that these “new” compounds were the α- and
β-dextrins. In fact, the existence of larger homologues of cycloamyloses was clearly
demonstrated a decade later by French. In 1957, French discovered delta-dextrin or
δ-dextrin and epsilon-dextrin or ε-dextrin, containing 9 and 10 units of glucose,
respectively (French 1957a, b). He proved their existence using radioautography
and chromatography measurements. However, French elucidated their structures
only in 1965 (French et al. 1965). At that time, French also wrote: “there is no obvious reason why the series should stop here” (French 1957a), suggesting the existence of cycloamyloses with 11 and 12 units of glucose, i.e., ξ-dextrin or zeta-dextrin
and η-dextrin or eta-dextrin, respectively. In the beginning of the 1960s, French
continued to study cycloamyloses with a larger ring. His objective was to develop a
fractionation method for isolation of larger homologues of cycloamyloses after
extensive β-amylase digestion to hydrolyze maltooligosaccharides. In 1961, the
existence of cycloamyloses with 11 and 12 units of glucose is confirmed using
radioautography (Pulley and French 1961), and 4 years later, he was the first to
propose a fractionation method for their isolation (French et al. 1965). The structure
and the dimensions of ξ-dextrin and η-dextrin are reported. French finally introduced the notion of Schardinger dextrin series, “a Schardinger dextrin family”
(French et al. 1965). The same year, Thoma and Stewart (1965) also published similar results, and the discovery of ξ-dextrin and η-dextrin is attributed to them (Caesar
1968; Szejtli 1998; Loftsson and Duchêne 2007).
N. Morin-Crini et al.
1.3.2 Native Cyclodextrins
Schardinger recognized only dextrin-α and dextrin-β, while Freudenberg obtained
γ-dextrin in 1948, although previously regarded by him as a cyclic heptasaccharide
(Freudenberg and Cramer 1948). Two years later, Freudenberg elucidated the structure of γ-dextrin (Freudenberg and Cramer 1950). The same year, using partial acid
hydrolysis and enzyme digestion followed by X-ray measurements and paper chromatography, French also elucidated the structure of γ-dextrin, first named cycloöctaamylose and later cyclooctaamylose (French et al. 1950b). This dextrin was
composed of eight glucose residues symmetrically arranged in a ring and linked
together by α-1,4-glucosidic bonds. In the late 1950s, French and co-workers had
established the molecular weight, the exact chemical structure, the dimensions, and
the types of bonding in the three cycloamyloses, cyclohexaamylose, cycloheptaamylose, and cyclooctaamylose, i.e., α-dextrin, β-dextrin, and γ-dextrin, respectively (French and McIntire 1950; Norberg and French 1950; French et al. 1950a, b).
In 1948, the first indications of the existence of higher homologues of dextrins
were published by Freudenberg and his young student Cramer (Freudenberg and
Cramer 1948). Two years later, French also suggested the possible existence of
cycloamyloses containing more than 8 glycosyl units (Norberg and French 1950;
French et al. 1950b). The same year, Akiya and co-workers claimed the “discovery
of new series of cyclic oligosaccharides” similar to the Schardinger dextrins, containing more than 8 glucose units (Akiya and Watanabe 1950a, b, c; Akiya and Okui
1951). Later, Caesar (1968) reported that these “new” compounds were the α- and
β-dextrins. In fact, the existence of larger homologues of cycloamyloses was clearly
demonstrated a decade later by French. In 1957, French discovered delta-dextrin or
δ-dextrin and epsilon-dextrin or ε-dextrin, containing 9 and 10 units of glucose,
respectively (French 1957a, b). He proved their existence using radioautography
and chromatography measurements. However, French elucidated their structures
only in 1965 (French et al. 1965). At that time, French also wrote: “there is no obvious reason why the series should stop here” (French 1957a), suggesting the existence of cycloamyloses with 11 and 12 units of glucose, i.e., ξ-dextrin or zeta-dextrin
and η-dextrin or eta-dextrin, respectively. In the beginning of the 1960s, French
continued to study cycloamyloses with a larger ring. His objective was to develop a
fractionation method for isolation of larger homologues of cycloamyloses after
extensive β-amylase digestion to hydrolyze maltooligosaccharides. In 1961, the
existence of cycloamyloses with 11 and 12 units of glucose is confirmed using
radioautography (Pulley and French 1961), and 4 years later, he was the first to
propose a fractionation method for their isolation (French et al. 1965). The structure
and the dimensions of ξ-dextrin and η-dextrin are reported. French finally introduced the notion of Schardinger dextrin series, “a Schardinger dextrin family”
(French et al. 1965). The same year, Thoma and Stewart (1965) also published similar results, and the discovery of ξ-dextrin and η-dextrin is attributed to them (Caesar
1968; Szejtli 1998; Loftsson and Duchêne 2007).
N. Morin-Crini et al.