13
and γ-dextrin, respectively (Freudenberg 1943). During the mid-1940s, there was
another system in current use (Crini 2014). In the alternate system, the number of
residues in the cyclic polymer was indicated by prefixing a Greek letter to the series
name. Since the smallest known cycloamylose was a hexamer, it was assigned the
prefix α. The cyclic heptatose, octaose, etc. were referred to, respectively, as β, γ,
etc. The first system introduced by French was however preferred because it was
more descriptive of the structures.
At the end of the 1940s, Cramer first proposed the cyclo-based nomenclature for
the nomenclature of the Schardinger dextrins, e.g., (6-ose)-cyclo, (7-ose)-cyclo, and
(8-ose)-cyclo for α-, β-, and γ-dextrins, respectively. For the first time in 1949,
Cramer introduced the term cyclodextrin. This name was included in the title of his
PhD dissertation entitled Die Cyclodextrine aus Stärke (Cramer 1949). For Cramer,
the term of cyclodextrin must be used to refer to cyclic oligosaccharides made up of
6, 7, or 8 units of D-glucose joined by α-(1 → 4) linkages termed α-, β-, and
γ-cyclodextrin, respectively. Because of its relative brevity, the term cyclodextrin
was soon accepted, but the nomenclature of cyclodextrins remained a subject of
debate until the end of the 1990s (Szejtli 1998; Loftsson and Duchêne 2007; Kurkov
and Loftsson 2013; Crini 2014; Morin-Crini et al. 2015). Indeed, at that time, several laboratories proposed clarifications of the nomenclature of cyclodextrins
because the term cyclodextrin only specified the nature of the sugars but did not give
any information on the bonding between them. Thus, the name cyclomaltohexaose
was suggested in 1997. This name is composed of first the term cyclo followed by a
term indicating the type of linkage, i.e., malto for glucose unit bound by α-(1→4)
linkages, and the number of sugar units with the ending ose, i.e., hexa for 6 or hepta
for 7. This final term, present in cyclomaltohexaose, implies a free anomeric center,
which is not present in cyclodextrins. Both the terms cyclodextrins and cyclomaltooligosaccharides were used (Crini 2014).
Other nomenclatures have also been proposed. For instance, α-cyclodextrin was
named cyclohexakis-(1→4)-α-D-glycosyl or cyclo-α-(1→4)-glucohexaoside. The
term of the glycosyl residue is preceded by the type of linkage between brackets,
which in turn is preceded by the term cyclo plus an indication of the number, i.e.,
cyclohexakis, etc. The literature uses all of these nomenclatures. Nevertheless, the
cyclodextrin-based nomenclature is still the most widely used in literature today.
The nomenclature for large-ring cyclodextrins, i.e., LR-CDs with a degree of
polymerization between 9 and >100, is more simple: each molecule is designated by
an abbreviation CDn where n indicates the number of glucose units in the macrocycle, e.g., CD14 (boat-like structure) composed of 14 glucose units (Morin-Crini
et al. 2015; Assaf et al. 2016; Sonnendecker and Zimmermann 2019a, b;
Sonnendecker et al. 2018, 2019).
1 History of Cyclodextrins
and γ-dextrin, respectively (Freudenberg 1943). During the mid-1940s, there was
another system in current use (Crini 2014). In the alternate system, the number of
residues in the cyclic polymer was indicated by prefixing a Greek letter to the series
name. Since the smallest known cycloamylose was a hexamer, it was assigned the
prefix α. The cyclic heptatose, octaose, etc. were referred to, respectively, as β, γ,
etc. The first system introduced by French was however preferred because it was
more descriptive of the structures.
At the end of the 1940s, Cramer first proposed the cyclo-based nomenclature for
the nomenclature of the Schardinger dextrins, e.g., (6-ose)-cyclo, (7-ose)-cyclo, and
(8-ose)-cyclo for α-, β-, and γ-dextrins, respectively. For the first time in 1949,
Cramer introduced the term cyclodextrin. This name was included in the title of his
PhD dissertation entitled Die Cyclodextrine aus Stärke (Cramer 1949). For Cramer,
the term of cyclodextrin must be used to refer to cyclic oligosaccharides made up of
6, 7, or 8 units of D-glucose joined by α-(1 → 4) linkages termed α-, β-, and
γ-cyclodextrin, respectively. Because of its relative brevity, the term cyclodextrin
was soon accepted, but the nomenclature of cyclodextrins remained a subject of
debate until the end of the 1990s (Szejtli 1998; Loftsson and Duchêne 2007; Kurkov
and Loftsson 2013; Crini 2014; Morin-Crini et al. 2015). Indeed, at that time, several laboratories proposed clarifications of the nomenclature of cyclodextrins
because the term cyclodextrin only specified the nature of the sugars but did not give
any information on the bonding between them. Thus, the name cyclomaltohexaose
was suggested in 1997. This name is composed of first the term cyclo followed by a
term indicating the type of linkage, i.e., malto for glucose unit bound by α-(1→4)
linkages, and the number of sugar units with the ending ose, i.e., hexa for 6 or hepta
for 7. This final term, present in cyclomaltohexaose, implies a free anomeric center,
which is not present in cyclodextrins. Both the terms cyclodextrins and cyclomaltooligosaccharides were used (Crini 2014).
Other nomenclatures have also been proposed. For instance, α-cyclodextrin was
named cyclohexakis-(1→4)-α-D-glycosyl or cyclo-α-(1→4)-glucohexaoside. The
term of the glycosyl residue is preceded by the type of linkage between brackets,
which in turn is preceded by the term cyclo plus an indication of the number, i.e.,
cyclohexakis, etc. The literature uses all of these nomenclatures. Nevertheless, the
cyclodextrin-based nomenclature is still the most widely used in literature today.
The nomenclature for large-ring cyclodextrins, i.e., LR-CDs with a degree of
polymerization between 9 and >100, is more simple: each molecule is designated by
an abbreviation CDn where n indicates the number of glucose units in the macrocycle, e.g., CD14 (boat-like structure) composed of 14 glucose units (Morin-Crini
et al. 2015; Assaf et al. 2016; Sonnendecker and Zimmermann 2019a, b;
Sonnendecker et al. 2018, 2019).
1 History of Cyclodextrins