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In organic chemistry, a lactol is a functional group which is the cyclic equivalent of a hemiacetal (−CH(OH)O−) or a hemiketal (>C(OH)O−). The compound is formed by the intramolecular , nucleophilic addition of a hydroxyl group ( −OH ) to the carbonyl group ( C=O ) of an aldehyde ( −CH=O ) or a ketone ( >C=O ).
Right: a lactol of fructose, a cyclic hemiketal. Hemiacetals commonly exist in nature as aldoses such as glucose , and hemiketals commonly exist in nature as ketoses such as fructose . The favorability of the formation of a strain-free six-membered ring and the electrophilicity of an aldehyde combine to strongly favor the acetal form.
Lactams can be formed from cyclisation of amino acids via the coupling between an amine and a carboxylic acid within the same molecule. Lactamization is most efficient in this way if the product is a γ-lactam.
Lactones are usually named according to the precursor acid molecule (aceto = 2 carbon atoms, propio = 3, butyro = 4, valero = 5, capro = 6, etc.), with a -lactone suffix and a Greek letter prefix that specifies the number of carbon atoms in the heterocycle — that is, the distance between the relevant -OH and the -COOH groups along said backbone.
This also allows for a classic use of Fétizon's reagent to form lactones from a primary diol. By oxidizing one of the alcohols to an aldehyde, the second alcohol equilibrates with the aldehyde to form a lactol which is reacted quickly with more Fétizon's reagent to trap the cyclic intermediate as a lactone. [8]
The protected erythrose product could then be converted to four possible sugars via Mukaiyama aldol addition followed by lactol formation. This requires appropriate diastereocontrol in the Mukaiyama aldol addition and the product silyloxycarbenium ion to preferentially cyclize, rather than undergo further aldol reaction.
Lactide is the lactone cyclic ester derived by multiple esterification between two (usually) or more molecules from lactic acid (2-hydroxypropionic acid) or other hydroxy carboxylic acid. They are designated as dilactides, trilactides, etc., according to the number of hydroxy acid residues.
2-Carboxybenzaldehyde is a chemical compound.It consists of a benzene ring, with an aldehyde and a carboxylic acid as substituents that are ortho to each other. The compound exhibits ring–chain tautomerism: the two substituents can react with each other to form 3-hydroxyphthalide, a cyclic lactol.