Introduction to Sugars and Lipids: Disaccharides

Vocabulary and key concepts from Lecture 4 on Disaccharide connectivity, nomenclature, Fischer glycosidation, and global protecting groups.

Glycosidic bond

The $C-O$ bond linking the anomeric center of one sugar to a second component; while usually oxygen-linked, others can include nitrogen, carbon, sulfur, or selenium.

Anomeric center

The hemiacetal or acetal carbon in a ring sugar, formed from the ring-closing reaction of the alcohol and carbonyl.

Anomeric effect

An electronic effect that favors electronegative substituents in the axial position at the anomeric center, often opposing steric effects which favor equatorial positions.

Reducing sugars

Hemiacetal sugars that can act as a reducing agent towards some metal salts, resulting in a color change.

Fischer glycosidation

The reaction of the hemiacetal form of a sugar with an alcohol under anhydrous Brønsted acid conditions (e.g., $SOCl_2$, $AcCl$, $ZnCl_2$) to form a glycoside.

Glycoside

A carbohydrate derivative formed when the hemiacetal form of a sugar reacts with an alcohol to yield an acetal.

Aglycone

The non-sugar unit attached to a sugar (glycone) to form a glycoside.

Glycosyl acceptor

A carbohydrate containing a free nucleophile that can react with a glycosyl donor to form a new glycosidic bond.

Glycosyl donor

A carbohydrate with a leaving group ($LG$) at the anomeric center which, after the leaving group leaves, forms an electrophilic glycosyl cation.

Activator

A reagent that helps the leaving group of a glycosyl donor leave more readily, aiding the formation of the electrophilic glycosyl cation.

Protecting groups

Chemical groups used to block reactions at specific hydroxyl groups (e.g., benzyl, esters, silyl) except for the one intended for glycosidic bond formation.

Global protecting groups

A type of protection that covers every hydroxyl group in a sugar ($1 imes$ primary, $3 imes$ secondary, and $1 imes$ anomeric secondary).

Acetyl group ($Ac_2O$)

An ester-based global protecting group applied using pyridine or $NaOAc$ and removed using $NaOH$ in $MeOH$.

Benzoyl group ($BzCl$)

An ester-based global protecting group applied using pyridine or $Et_3N$ and removed using $NaOMe$ in $MeOH$.

Benzyl group ($BnBr$)

An ether-based global protecting group applied using $NaH$ and removed via hydrogenolysis with $H_2, Pd/C$.