L14 Glycans (carbohydrates)

Carbohydrate nomenclature and functional groups

Formation of cyclic carbohydrates

Anomeric centres and anomers - what brings them about

Which of these would you expect to be preferentially formed

Despite the usual reasoning of steric clash disfavouring axial substituents, the alpha position is the most stable form with electronegative substituents

The anomeric effect - favouring alpha isomers

Glycosidic bonds overview

Can be O-glycosides or some other element

Fischer glycosylation mechanism

Requires quite concentrated acid and is not the most common synthesis method anymore

Challenges of disaccharide synthesis

Protection of the secondary alcohols only

Requires protecting the primary alcohol first separately

Silyl ether protecting groups

Selective protection and deprotection of C6-OH using silyl ethers

Selective deprotection of TBDMS using F- mechanism

Glycosylation - why is it always S_N1

Activators and leaving groups for glycosidic bond formation

n-Pentenyl glycoside activation

Why is glycosylation difficult to control the stereoselectivity of

How can you rectify this

Using ester protecting groups to drive both chemoselectivity and stereselectivity

Depending on the side of the ring the ester is on, it will block nucleophilic attack on that side, essentially locking the sterics of the product.