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Cyclic acetals are very much more stable against acid hydrolysis than acyclic acetals. Consequently acyclic acetals are used practically only when a very mild cleavage is required or when two different protected carbonyl groups must be differentiated in their liberation.
In organic chemistry, an acetonide is the functional group composed of the cyclic ketal of a diol with acetone. The more systematic name for this structure is an isopropylidene ketal. Acetonide is a common protecting group for 1,2- and 1,3-diols. [1] The protecting group can be removed by hydrolysis of the ketal using dilute aqueous acid.
The structure of the acetoxy group blue.. In organic chemistry, the acetoxy group (abbr. AcO or OAc; IUPAC name: acetyloxy [1]), is a functional group with the formula −OCOCH 3 and the structure −O−C(=O)−CH 3.
These protecting groups “lock” the sugars into a rigid chair conformation. When the sugar forms the necessary oxocarbenium ion, it flattens at the anomeric position. This change in configuration is a high-energy transformation when cyclic protecting groups are present, and leads to the sugar being “disarmed”. [3]
Formaldehyde forms a rich collection of acetals. This tendency reflects the fact that low molecular weight aldehydes are prone to self-condensation such that the C=O bond is replaced by an acetal. The acetal formed from formaldehyde (two hydrogens attached to the central carbon) is sometimes called a formal [4] or the methylenedioxy group.
The use of Fmoc as a temporary protecting group for amine at the N-terminus in solid phase synthesis is very widespread for Fmoc/tBu approach, because its removal with piperidine does not disturb the acid-labile linker between the peptide and the resin. [7]
However, in order for anomers to exist, the sugar must be in its cyclic form, since in open-chain form, the anomeric carbon atom is planar and thus achiral. More formally stated, then, an anomer is an epimer at the hemiacetal/hemiketal carbon atom in a cyclic saccharide. [1] Anomerization is the process of conversion of one anomer to the other.
Trimethyl orthoformate is a useful building block for creating methoxymethylene groups and heterocyclic ring systems. It introduces a formyl group to a nucleophilic substrate, e.g. RNH 2 to form R-NH-CHO, which can undergo further reactions.