19 - CARBOHYDRATES Flashcards
what is the structure of cellulose
what is starch made of
10-30% amylose
70-90% amylopectin
both have alpha glycosidic bonds
starch is digested by amylase (enzyme from saliva)
what is amylose made of
because of H bonding amylose has a spiral structure that has 6 units per turn
what is the test to detect starch
when starch is mixed with iodine in water
starch/iodine complex forms that has a very intense color
structure of amylopectin
digestion of cellulose
humans do not have enzymes that can hydrolyse the beta glycosidic bonds of cellulose
cows horses sheep goats and termites have symbiotic bacteria that possess the necessary enzymes to digest cellulose in the GI tract
structure of lactose and how it is digested
sucrose structure and how is it digested
two artificial sweeteners
invertase reaction
sucrose into glucose + fructose
called invertase because it inverts the sign of optical rotation
the composition of honey is similar
sucrose can also be broken down by acid hydrolysis (citric/absorbic acid)
where does digitoxin come from, structure and what is it used for?
materials for chemical synthesis of oligosaccharides
what does the stereochemistry of the anomeric center depend on
difficult to control
depends on nature of X on C2
leaving group of glycosyl acceptor and other factors
structure of cellobiose
what are the starting materials for the synthesis of cellobiose
why and how must the OH groups be protected
protecting the sugar OH groups prevents unwanted reactions
controls the position of the glycosydic bond
Tr=trityl
Ac=acetyl
keonigs knorr synthesis of cellobiose
how would you only form the alpha anomer with the koenigs knorr synthesis
how is the starting material X synthesized?
how is the starting material Y prepared?
what are the deprotection steps that need to happen to make cellobiose?
- NaOMe/MeOH which removes the Ac groups
- AcOH, heat which removes the trityl group
- alpha glycosidase enzyme (hydrolyses glycosidic bond)
removal of acetyl groups
how is the trityl group put on?
removal of trityl group
how can the relative rates of trityl cleavage be accelerated?
adding OMe groups will increase the rate of cleavage
what is another popular method for making oligosaccharides
using thio glycoside building blocks: more stable than halo sugars, easier to handle and store
glycosidic bond is activated by oxidation when desired
