Monosaccharides have the ability to react at the –O position in several different ways. In acidic conditions, monosaccharides can substitute selectively at the anomeric position to produce glycosides.
Concept: General Reaction5m
Hey guys. Now, let's talk about an -O site reaction of monosaccharides called n glycosidation. So, guys monosaccharides have the ability to react at the -O position or the oxygen position in several different ways, in acidic conditions monosaccharides can substitute selectively at the anomeric position only at the anomeric ition to produce what's known as glycosides. Remember, that glycosides would put basically like an R group or some kind of substituent over in the anomeric position okay? Well, it turns out that when nitrogenous, so I'm just going to put n, for nitrogenous and nucleophiles are used, meaning nucleophiles that get their lone pair or their nucleophilicity from a nitrogen, that substitution product is called an n-glycoside, okay? Because instead of forming an o-glycoside, meaning that you have a glycoside with an oxygen here, instead we're going to form a glyph glycosidic bond with a nitrogen containing compound, okay? Now, the term I'm going to use most of time for it is called an n-glycoside. So, it's very similar to o-glycoside so it's very easy to remember but another nomenclature term that you should just know is that n-glycosides are also referred to as glycosylamines, okay?. So, if you hear about glycosyl amine or like glycosylamines that is basically an amine being attached to a ring, to a furanose or a pyranose and it means the same thing as any glycoside, okay? So, as you can see in this reaction that i want to show you, this molecule could either being one amino d glucopyranoside because I'm saying that the glycoside is an amino group, one amino, or it can be referred to as the glucopyranosylamine because what we're saying is that it's the same as glucopyranose except that it happens to have an amine in the anomeric position, which is a glycose, which is a pyranosideamine, okay? Guys I'm not going to make you're not going to be accountable for this nomenclature but you should still recognize it, okay? Awesome, so let's go through the general reaction, the general reaction says that if you take a cyclic carbohydrate and then you react it with a nitrogen containing nucleophile, in this case I'm using the simplest one, which is ammonia, but it could have been a more complicated one, in acid what we're going to get is that the nitrogen attaches to the anomeric side and only the anomeric side and you're going to get a mixture of anomers with that nitrogen in the glycosidic bond, this is called the n glycosidic bond glycosidic link or bond, okay? I just want to make some points here. So, just you know why can it only react at the anomeric position and no other positions, why would you only substitute the n here and not, for example, at C2, guys, for the same exact reason, same exact mechanism as o-glycosidation. Remember, that in order for o-glycosidation to take place you need to pass through the oxo carbenium intermediate that stabilizes the positive charge right here, the same exact thing is going to happen with n-glycosidation where acid is going to come in kick out the water and going to form a double bond and put all that happens with n-glycosidation is that it's the last step nitrogen comes and attacks the positive charge here and then gets deprotonated and that is why we would get a nitrogen containing compounds looks very similar just at the anomeric position, cool? Awesome so that is that so far, in the next video I'm going to talk to you guys about specific types of n-glycosides that are called ribonucleosides.
Concept: Creating Ribonucleosides6m
Note: The Adenine and Guanine structures should be switched. :)
Problem: Propose an acid-catalyzed mechanism by which cytosine can form a β-1 N-linkage with 2-deoxy-β-Dribofuranose to produce a deoxynucleoside (DNA) called deoxycytidine.9m