D-Galactopyranose pentaacetate
[CAS# 25878-60-8]

Identification

• Classification: Biochemical >> Carbohydrate >> Monosaccharide
• Name: D-Galactopyranose pentaacetate
• Synonyms: 1,2,3,4,6-Penta-O-acetyl-D-galactopyranose
• Molecular Formula: C₁₆H₂₂O₁₁
• Molecular Weight: 390.34
• CAS Registry Number: 25878-60-8
• EC Number: 898-007-4
• SMILES: CC(=O)OC[C@@H]1[C@@H]([C@@H]([C@H](C(O1)OC(=O)C)OC(=O)C)OC(=O)C)OC(=O)C

Properties

• Density: 1.3±0.1 g/cm³ Calc.^*
• Boiling point: 434.8±45.0 °C 760 mmHg (Calc.)^*
• Flash point: 188.1±28.8 °C (Calc.)^*
• Index of refraction: 1.482 (Calc.)^*

^* Calculated using Advanced Chemistry Development (ACD/Labs) Software.

Safety Data

• Hazard Symbols: GHS07 Warning
• Risk Statements: H315-H319-H335
• Safety Statements: P261-P264-P264+P265-P271-P280-P302+P352-P304+P340-P305+P351+P338-P319-P321-P332+P317-P337+P317-P362+P364-P403+P233-P405-P501

Hazard Classification

Hazard	Class	Category Code	Hazard Statement
Specific target organ toxicity - single exposure	STOT SE	3	H335
Eye irritation	Eye Irrit.	2A	H319
Skin irritation	Skin Irrit.	2	H315

Discovery and Applications

D-Galactopyranose pentaacetate is the fully acetylated derivative of D-galactopyranose in which all five hydroxyl groups of the monosaccharide are converted to acetate esters. D-galactose was identified in the nineteenth century during investigations of lactose hydrolysis, when it was recognized as one of the constituent sugars of milk sugar. Subsequent structural studies established that D-galactose is an aldohexose closely related to D-glucose, differing in configuration at the C-4 position. The pyranose form, a six-membered cyclic hemiacetal, was shown to predominate in solution and in crystalline derivatives.

The preparation of peracetylated sugars such as D-galactopyranose pentaacetate emerged as a central method in classical carbohydrate chemistry. Treatment of D-galactose with acetic anhydride, commonly in the presence of basic catalysts such as pyridine or sodium acetate, converts the hydroxyl groups at positions 1, 2, 3, 4, and 6 into acetate esters. This reaction proceeds under controlled conditions to minimize degradation and yields a crystalline product that is significantly less hygroscopic than the parent sugar. The formation of well-defined acetylated derivatives provided chemists with stable compounds suitable for purification and analysis at a time when spectroscopic methods were not yet available.

D-galactopyranose pentaacetate played an important role in confirming the ring size and configuration of galactose. The isolation of distinct anomeric forms, corresponding to alpha and beta configurations at the anomeric carbon, supported the concept of mutarotation and the cyclic structure of monosaccharides. Measurement of melting points, optical rotation, and derivative interconversions allowed researchers to compare theoretical structural proposals with experimental results. These studies contributed to the broader validation of the Haworth representation of pyranose sugars and to the systematic understanding of stereochemistry in carbohydrates.

Beyond structural elucidation, D-galactopyranose pentaacetate has served as a versatile intermediate in synthetic carbohydrate chemistry. The acetyl groups protect the hydroxyl functions, reducing intermolecular hydrogen bonding and increasing solubility in organic solvents such as chloroform, dichloromethane, and ethyl acetate. This property enables further transformations that would be difficult to achieve with the free sugar. In particular, activation of the anomeric acetate under suitable conditions allows the compound to function as a glycosyl donor in the synthesis of glycosides. Controlled deacetylation can subsequently regenerate specific hydroxyl groups for additional modification.

Peracetylated monosaccharides have also been used in mechanistic studies of glycosylation reactions. The electron-withdrawing nature of the acetyl substituents influences the stability of intermediate species formed during substitution at the anomeric center. Experimental investigations of reaction rates and stereochemical outcomes have relied on compounds such as D-galactopyranose pentaacetate to clarify principles governing neighboring group participation and anomeric selectivity. These findings have had lasting impact on the design of oligosaccharide synthesis strategies.

In addition, acetylated galactose derivatives have been employed as starting materials in the preparation of biologically relevant molecules, including galactosides and glycoconjugates. The controlled protection and deprotection sequences made possible by acetyl groups have enabled the stepwise assembly of more complex carbohydrate structures. Although D-galactopyranose pentaacetate itself is primarily an intermediate rather than an end-use product, its historical and practical importance is well documented in the literature of carbohydrate chemistry.

Through its contribution to structural analysis, synthetic methodology, and mechanistic understanding, D-galactopyranose pentaacetate exemplifies the role of protected sugar derivatives in the advancement of glycochemistry. Its preparation and applications are grounded in experimentally established principles that continue to inform modern research in carbohydrate science.

References

2023. A guide for the synthesis of key nucleoside scaffolds in drug discovery. Medicinal Chemistry Research.
DOI: 10.1007/s00044-023-03096-w

2021. Synthesis of a Key Subunit of HIV-1 Protease Inhibitor Darunavir. Synfacts.
DOI: 10.1055/s-0040-1719792

2019. Synthesis of a cGAMP Analogue. Synfacts.
DOI: 10.1055/s-0037-1612408