Disaccharides: Stereoselective Synthesis Flashcards

Flashcards covering stereoselective disaccharide synthesis, including protecting groups, chemical methods like trichloroacetimidates and NGP, and biological enzymatic pathways.

Bulky silyl groups

Groups used to protect the primary hydroxyl ($C6$) only.

Fischer glycosidation

A process that protects the anomeric centre hydroxyl ($C1$) only.

Cyclic benzylidenes

Protecting groups for $C4$ and $C6$ positions.

Cyclic acetonides

Protecting groups that target $1,2 ext{-cis}$ diols.

Trans-decalins

Protecting groups that target $1,2 ext{-trans}$ diols.

Cellulose

A major component of plant cell walls containing eta-(1 ightarrow4) ext{-glycosidic} bonds.

Maltose

An edible 'malt sugar' containing eta-(1 ightarrow4) ext{-glycosidic} bonds.

Amylose

Edible starch found in potatoes containing eta-(1 ightarrow4) ext{-glycosidic} bonds.

Trehalose

An energy source in many bacteria, fungi, and invertebrates containing eta-(1 ightarrow1) ext{-glycosidic} bonds that lowers the freezing point of water.

Glycogen

Short-term energy storage in animals containing linear eta-(1 ightarrow4) ext{-glycosidic} bonds and eta-(1 ightarrow6) ext{-glycosidic} bond branch points.

Trichloroacetimidates with $NaH$

Conditions providing thermodynamic control where the major product is axial due to the anomeric effect.

Trichloroacetimidates with $K_2CO_3$

Conditions providing kinetic control where the major product is equatorial due to sterics.

Neighbouring group participation (NGP)

A strategy using an ester group at the $C2$ position to form a cyclic oxonium ion, yielding $1,2 ext{-trans}$ glycosides.

Acetonitrile ($MeCN$)

A solvent that can be used to selectively make $\beta ext{-linked}$ glycosides from donors without a participating group at $C2$.

Glycosyltransferases

Enzymes that form new glycosidic bonds between saccharides.

Glycosidases

Enzymes that break glycosidic bonds through a hydrolysis mechanism.

Polysaccharide lysases

Enzymes that break glycosidic bonds through an anti-$\beta ext{-elimination}$ mechanism.

Carbohydrate esterases

Enzymes that cleave esters.

Uridine diphosphate galactose ($UDP ext{-Gal}$)

A nucleotide phosphate serving as nature's equivalent to a good leaving group for galactosyltransferases.

Inverting glycosyltransferases

Enzymes that use an $S_N2$ mechanism to cause inversion of stereochemistry at the anomeric centre.

Koshland-type retaining mechanism

A proposed enzyme mechanism involving two $S_N2$ inversions to achieve overall retention of stereochemistry at the anomeric centre.

$S_Ni$ mechanism

Nucleophilic substitution with internal return where the leaving group departs and the nucleophile attacks from the same face.