Natural occurrence and preparation of O-acylated 2,3-unsaturated sialic acids

Chemical Diversity in the Sialic Acids and Related α-Keto Acids: An Evolutionary Perspective

“…Intra- or intermolecular lactonization involving the carboxylate at C1 and intramolecular lactamization between C1 and C5 (in case of Neu) add further variety. Some sialic acids (e.g., 2-deoxy-2,3-didehydro sialic acids) are found only in free form, as expected from the lack of the α-keto group . There are some other sialic acid-like molecules with a nine-carbon backbone found so far only in bacteria, such as derivatives of legionaminic acid (Figure C) and pseudaminic acid (Figure D).…”

“…Some sialic acids (e.g., 2-deoxy-2,3-didehydro sialic acids) are found only in free form, as expected from the lack of the R-keto group. 11 There are some other sialic acid-like molecules with a nine-carbon backbone found so far only in bacteria, such as derivatives of legionaminic acid (Figure 1C) and pseudaminic acid (Figure 1D). As discussed below, these molecules may be synthesized via very similar biosynthetic pathways to those of sialic acids, 12 raising the possibility of expanding the definition of sialic acids to accommodate them.…”

Chemistry, biochemistry and biology of sialic acids

“…Due to hydrogen bonding of HO7 and H08, leading to a trans-orientation of these groups, the glycerol side chain is not as flexible as one might expect. Moreover, they can be generated from corresponding CMP-N-acylneuraminic acids in a non-enzymatic elimination reaction, occurring under physiological and, much faster, under alkaline conditions [34,35]. Free sialic acids have mainly the b-anomeric ring structure (>93%), whereas glycoconjugate-bound sialic acids occur specifically in the a-anomeric form [54].…”

Exploration of the Sialic Acid World

“…636,637 A number of other naturally occurring sialic acids have also been synthesized along organic chemical or aldolase-catalyzed routes. Examples are as follows: Neu2en5Ac, 638 Neu2en5Gc, 75,638 Neu2en5,9Ac 2 , 56 Neu2en5, 7,9Ac 3 , 56 Neu2en9Ac5Gc, 56 Neu2en5GcAc, 56 Kdn, [639][640][641] Kdn2en, 642 Neu2, 7an5Ac, 643,644 Neu5Ac8Me, 645 Neu5Ac9P, 51 Neu5Ac1,7lactone, [646][647][648] Neu5Gc1,7lactone, 647 and Kdn1,7lactone. 647 See also refs.…”