Sialic acids and other Nonulosonic acids (NulOs)

Reference: Cataloging natural sialic acids and other nonulosonic acids (NulOs), and their representation using the Symbol Nomenclature for Glycans, Glycobiology 33: 99-103, 2023. Citation link (PMID 36648443).

Sialic acids (Sia) are a family of related monosaccharides commonly present in higher animals like Echinoderma, Hemichorda, Cephalocorda, and Vertebrata. Sialic acids commonly occur as terminal and sometimes as internal residues in glycoconjugates and other carbohydrates, e.g. glycoproteins, glycolipids, lipooligo- & capsular-polysaccharides, tissue polysialic acids, oligosaccharides, and exopolysaccharides. Due to their common terminal presentation on cell surface glycans, they facilitate numerous key biological functions related to cellular recognition, cell adhesion, communication/signaling, control of glycoconjugate half-life in circulation, tumor growth and metastasis, developmental programming, immune regulation, and host interaction with viruses and bacteria, including commensals, symbionts, and opportunistic pathogens.

Sialic acids are a subclass of a superfamily called non-2-ulosonic acids, nonulosonic acids (2-ketoaldonic acids; α-ketoaldonic acids) or "NulOs". The simplest compound in this class is neuraminic acid or Neu (Figure 1), a 3-deoxy, 5-amino form of the nine-carbon base nonulosonic acid, with hydroxyl groups at C4, C7, C8 and C9 conforming with the D-glycero-D-galacto configuration. This molecule contains a 2-keto carboxylic acid group that facilitates C2-O-C6 ring closure. The common intramolecular (cyclic) hemiketal form of Neu is a pyranose ring with ²C₅ chair conformation and an equatorially oriented glycerol chain at C6. Addition of a substituent N-acetyl at C5 results in Neu5Ac (N-acetylneuraminic acid). Hydroxylation of the N-acetyl group of Neu5Ac results in Neu5Gc (N-glycolylneuraminic acid). Replacement of the C5 amine with hydroxyl results in Kdn. Neu5Ac, Neu5Gc and Kdn are the most common structural relatives of Neu. These deoxy-nonulosonic acids (deoxy at C3, in all cases) can be further modified by various substituents to result in over 90 additional naturally occurring members of the sialic acid family (Table 1 below).

Figure 1: 3-Deoxy-non-2-ulosonic acids (sialic acid subclass):

A. 5-Amino-3,5-dideoxy-D-glycero-D-galacto-non-2-ulosonic acid (neuraminic acid, Neu);
B. 5-Acetamido-3,5-dideoxy-D-glycero-D-galacto-non-2-ulosonic acid (N-acetylneuraminic acid, Neu5Ac);
C. 3,5-Dideoxy-5-hydroxyacetamido-D-glycero-D-galacto-non-2-ulosonic acid (N-glycolylneuraminic acid, Neu5Gc);
D. 3-Deoxy-D-glycero-D-galacto-non-2-ulosonic acid (2-keto-3-deoxy-nononic acid, ketodeoxynononic acid, Kdn).

The ²C₅ chair conformations of Neu, Neu5Ac, Neu5Gc and Kdn are presented in the α-configuration (C2).

In addition to the above, another "sialic-acid-like" subclass of the NulO superfamily exists based on modifications of dideoxy-nonulosonic acid (deoxy at C3 and C9, in all cases). These were originally identified in bacterial lipopolysaccharides, capsular polysaccharides and glycoproteins. The parent compound (5,7-diamino-3,5,7,9-tetradeoxy-non-2-ulosonic acid) in this class contains a terminal methyl group as C9 and aminodeoxy functions at C5 and C7. Six further subclasses have been defined including pseudaminic acid (Pse), legionaminic acid (Leg), 4-epi-legionaminic acid (4eLeg), 8-epi-legionaminic acid (8eLeg), acinetaminic acid (Aci) and 8-epi-acinetaminic acid (8eAci) (Figure 2). A survey of over 50 known structures of naturally occurring 5,7-diamino-3,5,7,9-tetradeoxy-non-2-ulosonic acid derivatives, together with some related 9-deoxy-non-2-ulosonic acids, is presented in Table 2.

NulO biosynthetic pathways couple pyruvate with a hexose (e.g. D-mannose), a N-acetylhexosamine (2-acetamido-2-deoxy-hexose, e.g. N-acetyl-D-mannosamine), or a 2,4-diacetamido-2,4,6-trideoxy-hexose. The hexose (variant) C1-C6 chain becomes carbon 4 to 9 in the NulO, while carbon positions 1 to 3 are contributed by pyruvate. According to IUPAC/IUBMB rules, naming of hexose configurations refers to the first four chiral atoms. In NulO biosynthesis, a new chiral atom is created at C4, generating a seeming incongruence between the nomenclature and how these biological molecules come together in nature. For example, the sialic acid Neu5Ac (5-acetamido-3,5-dideoxy-D-glycero-D-galacto-non-2-ulosonic acid) is formed from N-acetyl-D-mannosamine, with the D-manno becoming C5 to C8 without a change in configuration. However, the new chiral atom created at C4 shifts the nomenclature to instead refer to positions C4 to C7, thus adopting a D-galacto configuration. The D-glycero part of the IUPAC name refers to the configuration at C8, changes to which do not impact the ring configuration. Some aspects of NulO biosynthesis are different between prokaryotes and eukaryotes. However, all NulOs share the unique feature (among the monosaccharides) of being activated using cytidine triphosphate (CTP) as an energy source to create the CMP-NulO donor.

Figure 2: 3,9-Dideoxy-non-2-ulosonic acids (sialic-acid-like subclass):

A. 5,7-Diamino-3,5,7,9-tetradeoxy-L-glycero-L-manno-non-2-ulosonic acid (pseudaminic acid, Pse);
B. 5,7-Diamino-3,5,7,9-tetradeoxy-D-glycero-D-galacto-non-2-ulosonic acid (legionaminic acid, Leg);
C. 5,7-Diamino-3,5,7,9-tetradeoxy-D-glycero-D-talo-non-2-ulosonic acid (4-epi-legionaminic acid, 4eLeg);
D. 5,7-Diamino-3,5,7,9-tetradeoxy-L-glycero-D-galacto-non-2-ulosonic acid (8-epi-legionaminic acid, 8eLeg);
E. 5,7-Diamino-3,5,7,9-tetradeoxy-L-glycero-L-altro-non-2-ulosonic acid (acinetaminic acid, Aci);
F. 5,7-Diamino-3,5,7,9-tetradeoxy-D-glycero-L-altro-non-2-ulosonic acid (8-epi-acinetaminic acid, 8eAci).

The ²C₅ chair conformations are presented in the β-configuration (C2) for Pse, Aci and 8eAci and in the α-configuration (C2) for Leg, 4eLeg and 8eLeg. Note that in all cases the carboxyl function at C2 has an axial orientation.

Table 1 Reported structures of naturally occurring members of the sialic acid family based on NMR and/or mass spectrometry reports.
(updated survey since the publication of R. Schauer & J.P. Kamerling, Exploration of the Sialic Acid World, Adv. Carbohydr. Chem. Biochem. 2018, 75, 1-213; combined with SNFG symbols) (Download TSV data file)

Name	Abbreviation	CID	SID	References	Database links
5-Amino-3,5-dideoxy-D-glycero-D-galacto-non-2-ulosonic acid / neuraminic acid (Neu)	Neu	441037	252301019	1, 2, 3, 4, 5, 6	[CSDB]
Neuraminic acid 1,5-lactam^b,i	Neu1,5lactam	168009038	480493132	6, 7
5-N-Acetyl-neuraminic acid (N-Acetylneuraminic acid) Neu5Ac	Neu5Ac	439197	252089093	5, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20	[CSDB1][CSDB2] [CSDB3] [CSDB4] [CSDB5]
5-N-Acetyl-4-O-acetyl-neuraminic acid	Neu4,5Ac₂	92042742	480493133	5, 8, 10, 11, 14, 16, 17, 18, 19, 20, 21
5-N-Acetyl-7-O-acetyl-neuraminic acid	Neu5,7Ac₂	92042743	480493134	5, 8, 10, 11, 16, 17, 18, 19, 20, 22, 23, 24, 25
5-N-Acetyl-8-O-acetyl-neuraminic acid	Neu5,8Ac₂	129677032	480493135	5, 8, 17, 19, 20, 24
5-N-Acetyl-9-O-acetyl-neuraminic acid	Neu5,9Ac₂	92042744	480493136	5, 8, 14, 16, 17, 18, 19, 20, 23, 24, 25, 26
5-N-Acetyl-4,9-di-O-acetyl-neuraminic acid	Neu4,5,9Ac₃	129711380	480493137	5, 8, 14, 17, 20
5-N-Acetyl-7,8-di-O-acetyl-neuraminic acid	Neu5,7,8Ac₃	168009039	480493138	22
5-N-Acetyl-7,9-di-O-acetyl-neuraminic acid	Neu5,7,9Ac₃	129711399	480493139	5, 8, 14, 16, 17, 18, 19, 20, 24, 25, 27
5-N-Acetyl-8,9-di-O-acetyl-neuraminic acid	Neu5,8,9Ac₃	129716696	480493140	5, 8, 16, 17, 18, 19, 20, 24, 25, 27
5-N-Acetyl-4,7,9-tri-O-acetyl-neuraminic acid	Neu4,5,7,9Ac₄	140507949	480493141	5
5-N-Acetyl-7,8,9-tri-O-acetyl-neuraminic acid	Neu5,7,8,9Ac₄	129711405	480493142	8, 17, 18, 19, 20, 24
5-N-Acetyl-4,7,8,9-tetra-O-acetyl-neuraminic acid	Neu4,5,7,8,9Ac₅	11733494	480493143	5
5-N-Acetyl-4-O-glycolyl-neuraminic acid	Neu5Ac4Gc	168009040	480493144	28
5-N-Acetyl-7-O-glycolyl-neuraminic acid	Neu5Ac7Gc	168009041	480493145	28
5-N-Acetyl-9-O-lactyl-neuraminic acid^c	Neu5Ac9Lt	129729663	480493146	5, 8, 17, 19, 20, 29, 30
5-N-Acetyl-4-O-acetyl-9-O-lactyl-neuraminic acid	Neu4,5Ac₂9Lt	129800763	480493147	5, 8, 17, 20, 31
5-N-Acetyl-7-O-acetyl-9-O-lactyl-neuraminic acid	Neu5,7Ac₂9Lt	140507951	480493148	5
5-N-Acetyl-8-O-acetyl-9-O-lactyl-neuraminic acid	Neu5,8Ac₂9Lt	168009042	480493149	32
5-N-Acetyl-8-O-methyl-neuraminic acid	Neu5Ac8Me	14160881	480493150	5, 8, 12, 20, 33
5-N-Acetyl-4-O-acetyl-8-O-methyl-neuraminic acid	Neu4,5Ac₂8Me	168009043	480493151	5
5-N-Acetyl-9-O-acetyl-8-O-methyl-neuraminic acid	Neu5,9Ac₂8Me	140507954	480493152	5, 8, 20, 33
5-N-Acetyl-9-O-methyl-neuraminic acid	Neu5Ac9Me	168009044	480493153	34
5-N-Acetyl-4-O-sulpho-neuraminic acid	Neu5Ac4S	168009045	480493154	35
5-N-Acetyl-8-O-sulpho-neuraminic acid	Neu5Ac8S	129681273	480493155	5, 19, 36, 37
5-N-Acetyl-4-O-acetyl-8-O-sulpho-neuraminic acid	Neu4,5Ac₂8S	140507948	480493156	5
5-N-Acetyl-9-O-phospho-neuraminic acid^d	Neu5Ac9P	440962	480493157	38
5-N-Acetyl-2-deoxy-2,3-didehydro-neuraminic acid^d,i	Neu2en5Ac	65309	480493158	8, 17, 20, 30, 39, 40, 41
5-N-Acetyl-9-O-acetyl-2-deoxy-2,3-didehydro-neuraminic acid^d,i	Neu2en5,9Ac₂	102169087	480493159	42, 43
5-N-Acetyl-2-deoxy-2,3-didehydro-9-O-lactyl-neuraminic acid^d,i	Neu2en5Ac9Lt	168009046	480493160	42, 43
5-N-Acetyl-2,7-anhydro-neuraminic acid^d,i	Neu2,7an5Ac	449401	480493161	8, 20, 42, 44, 45, 46
5-N-Acetyl-4,8-anhydro-neuraminic acid^e,i	Neu4,8an5Ac	14283565	480493162	18, 19, 47, 48
5-N-Acetyl-neuraminic acid 1,7-lactoneⁱ	Neu1,7lactone5Ac	102027926	480493163	5, 49, 50
5-N-Acetyl-9-O-acetyl-neuraminic acid 1,7-lactoneⁱ	Neu1,7lactone5,9Ac₂	168009047	480493164	5
5-N-Acetyl-4,9-di-O-acetyl-neuraminic acid 1,7-lactoneⁱ	Neu1,7lactone4,5,9Ac₃	168009048	480493165	5
1-Tauryl 5-N-acetyl-neuraminic amide	Neu5Ac1Tau	168009049	480493166	51
5-N-Glycolyl-neuraminic acid (N-Glycolylneuraminic acid) Neu5Gc	Neu5Gc	440001	252089091	5, 8, 10, 13, 14, 16, 17, 18, 19, 20, 52, 53, 54	[CSDB]
4-O-Acetyl-5-N-glycolyl-neuraminic acid	Neu4Ac5Gc	129674796	480493167	8, 14, 17, 18, 19, 20, 28	[CSDB]
7-O-Acetyl-5-N-glycolyl-neuraminic acid	Neu7Ac5Gc	140387950	480493168	8, 17, 19, 20, 24
8-O-Acetyl-5-N-glycolyl-neuraminic acid	Neu8Ac5Gc	140507946	480493169	19, 42
9-O-Acetyl-5-N-glycolyl-neuraminic acid	Neu9Ac5Gc	129775298	480493170	5, 8, 14, 16, 17, 18, 19, 20, 24
4,7-Di-O-acetyl-5-N-glycolyl-neuraminic acid	Neu4,7Ac₂5Gc	140507953	480493171	5
4,9-Di-O-acetyl-5-N-glycolyl-neuraminic acid	Neu4,9Ac₂5Gc	129800727	480493172	5
7,9-Di-O-acetyl-5-N-glycolyl-neuraminic acid	Neu7,9Ac₂5Gc	140387948	480493173	5, 8, 17, 18, 19, 20, 24
8,9-Di-O-acetyl-5-N-glycolyl-neuraminic acid	Neu8,9Ac₂5Gc	129716700	480493174	5, 8, 17, 18, 19, 20, 24
4,7,9-Tri-O-acetyl-5-N-glycolyl-neuraminic acid	Neu4,7,9Ac₃5Gc	168009050	480493175	5
7,8,9-Tri-O-acetyl-5-N-glycolyl-neuraminic acid	Neu7,8,9Ac₃5Gc	129716704	480493176	8, 17, 18, 20, 24
4,7,8,9-Tetra-O-acetyl-5-N-glycolyl-neuraminic acid	Neu4,7,8,9Ac₄5Gc	168009051	480493177	5
5-N-Glycolyl-9-O-lactyl-neuraminic acid	Neu5Gc9Lt	140372591	480493178	5, 19, 42
4-O-Acetyl-5-N-glycolyl-9-O-lactyl-neuraminic acid	Neu4Ac5Gc9Lt	140387947	480493179	5
7-O-Acetyl-5-N-glycolyl-9-O-lactyl-neuraminic acid	Neu7Ac5Gc9Lt	168009052	480493180	5
8-O-Acetyl-5-N-glycolyl-9-O-lactyl-neuraminic acid	Neu8Ac5Gc9Lt	140507950	480493181	5
4,7-Di-O-acetyl-5-N-glycolyl-9-O-lactyl-neuraminic acid	Neu4,7Ac₂5Gc9Lt	140507945	480493182	5
7,8-Di-O-acetyl-5-N-glycolyl-9-O-lactyl-neuraminic acid	Neu7,8Ac₂5Gc9Lt	140507955	480493183	5
5-N-Glycolyl-8-O-methyl-neuraminic acid	Neu5Gc8Me	129800653	480493184	8, 18, 19, 20, 33, 55, 56
4-O-Acetyl-5-N-glycolyl-8-O-methyl-neuraminic acid	Neu4Ac5Gc8Me	168009053	480493185	57
7-O-Acetyl-5-N-glycolyl-8-O-methyl-neuraminic acid	Neu7Ac5Gc8Me	168009054	480493186	19, 57
9-O-Acetyl-5-N-glycolyl-8-O-methyl-neuraminic acid	Neu9Ac5Gc8Me	129829096	480493187	8, 18, 19, 20, 33, 42
4,7-Di-O-acetyl-5-N-glycolyl-8-O-methyl-neuraminic acid	Neu4,7Ac₂5Gc8Me	168009055	480493188	57
7,9-Di-O-acetyl-5-N-glycolyl-8-O-methyl-neuraminic acid	Neu7,9Ac₂5Gc8Me	129829113	480493189	18
5-N-Glycolyl-9-O-methyl-neuraminic acid	Neu5Gc9Me	168009056	480493190	34, 58
5-N-Glycolyl-8-O-sulpho-neuraminic acid	Neu5Gc8S	129681276	480493191	5, 19, 36, 59
5-N-Glycolyl-9-O-sulpho-neuraminic acid	Neu5Gc9S	140507947	480493192	60
5-N-(O-Acetyl)glycolyl-neuraminic acid	Neu5(Gc2Ac)	129752159	480493193	8, 20, 61
5-N-(O-Methyl)glycolyl-neuraminic acid	Neu5(Gc2Me)	168009057	480493194	62
2-Deoxy-2,3-didehydro-5-N-glycolyl-neuraminic acid^d,i	Neu2en5Gc	3082514	480493195	8, 20, 43, 63
9-O-Acetyl-2-deoxy-2,3-didehydro-5-N-glycolyl-neuraminic acid^d,i	Neu2en9Ac5Gc	162884378	480493196	43
2-Deoxy-2,3-didehydro-5-N-glycolyl-9-O-lactyl-neuraminic acid^d,i	Neu2en5Gc9Lt	168009058	480493197	42, 43
2-Deoxy-2,3-didehydro-5-N-glycolyl-8-O-methyl-neuraminic acid^d,i	Neu2en5Gc8Me	168009059	480493198	42
2,7-Anhydro-5-N-glycolyl-neuraminic acid^d,i	Neu2,7an5Gc	101638299	480493199	20, 42, 45
2,7-Anhydro-5-N-glycolyl-8-O-methyl-neuraminic acid^d,i	Neu2,7an5Gc8Me	168009060	480493200	42
4,8-Anhydro-5-N-glycolyl-neuraminic acid^e,i	Neu4,8an5Gc	168009061	480493201	19
5-N-Glycolyl-neuraminic acid 1,7-lactoneⁱ	Neu1,7lactone5Gc	168009062	480493202	5
9-O-Acetyl-5-N-glycolyl-neuraminic acid 1,7-lactoneⁱ	Neu1,7lactone9Ac5Gc	168009063	480493203	5
7-Acetamido-9-O-acetyl-7-deoxy-5-N-glycolyl-neuraminic acid^f,g	Neu9Ac5Gc7NAc	168009064	480493204	5
7-Acetamido-8,9-di-O-acetyl-7-deoxy-5-N-glycolyl-neuraminic acid^f,g,h	Neu8,9Ac₂5Gc7NAc	168009065	480493205	5
3-Deoxy-D-glycero-D-galacto-non-2-ulosonic acid / 2-keto-3-deoxy-nononic acid (Kdn)	Kdn	13991616	252089089	5, 19, 64, 65, 66	[CSDB]
5-O-Acetyl-2-keto-3-deoxy-nononic acid	Kdn5Ac	168009066	480493206	5, 19
7-O-Acetyl-2-keto-3-deoxy-nononic acid	Kdn7Ac	168009067	480493207	5, 19
8-O-Acetyl-2-keto-3-deoxy-nononic acid	Kdn8Ac	168009068	480493208	67
9-O-Acetyl-2-keto-3-deoxy-nononic acid	Kdn9Ac	14633447	480493209	5, 19, 68
4,5-Di-O-acetyl-2-keto-3-deoxy-nononic acid	Kdn4,5Ac₂	168009069	480493210	5
4,7-Di-O-acetyl-2-keto-3-deoxy-nononic acid	Kdn4,7Ac₂	168009070	480493211	5
5,9-Di-O-acetyl-2-keto-3-deoxy-nononic acid	Kdn5,9Ac₂	168009071	480493212	19
7,9-Di-O-acetyl-2-keto-3-deoxy-nononic acid	Kdn7,9Ac₂	168009072	480493213	5, 19
8,9-Di-O-acetyl-2-keto-3-deoxy-nononic acid	Kdn8,9Ac₂	168009073	480493214	5
2-Keto-3-deoxy-4-O-methyl-nononic acid	Kdn4Me	168009074	480493215	69	[CSDB]
2-Keto-3-deoxy-5-O-methyl-nononic acid	Kdn5Me	168009075	480493216	70	[CSDB]
2-Keto-3-deoxy-9-O-methyl-nononic acid	Kdn9Me	168009076	480493217	71	[CSDB]
(R)-7,9-O-[1-Carboxyethylidene]-2-keto-3-deoxy-nononic acid	Kdn7,9Pyr_R	168009077	480493218	72	[CSDB]
2-Keto-3-deoxy-9-O-phospho-nononic acid^d	Kdn9P	124037361	480493219	73

^aPresent only in bound form, and considered to be derived from bound Neu5Ac in an enzymatic de-N-acetylation/re-N-acetylation cycle.

^b Present only in bound form, and considered to be derived from bound Neu in an enzymatic dehydration reaction, catalyzed by a so-called sialic acid cyclase. Neu1,5lactam was initially called ‘cyclic sialic acid’.

^c Lactyl = L-Lactyl.

^d Present only in free form.

^e Neu4,8an5Ac does not occur as such in nature. It is assumed to be formed under hydrolytic conditions from bound Neu4,5Ac₂.

^fThe D-glycero-D-galacto configuration has not been verified by the authors.

^gCompared with Ref. 5, 7Am has been changed into 7NAc.

^hNeu4,9Ac₂7Am5Gc in the text of Ref. 5 is probably a typing error for Neu8,9Ac₂7Am5Gc.

ⁱ'en' (didehydro) is 2-3, 'an' (anhydro) is 2-7, 'on' (lactone) is 1-7, and 'am' (lactam) is 1-5, by default, unless specify otherwise in legend, e.g. 4-8.

Table 2 Reported structures of naturally occurring 5,7-Diamino-3,5,7,9-tetradeoxy-non-2-ulosonic acid derivatives, and some related structures based on NMR and/or mass spectrometry reports.
(updated survey since the publication of R. Schauer & J.P. Kamerling, Exploration of the Sialic Acid World, Adv. Carbohydr. Chem. Biochem. 2018, 75, 1-213; combined with SNFG symbols) (Download TSV data file)

Name	Abbreviation	CID	SID	References	Database Links
5,7-Diamino-3,5,7,9-tetradeoxy-L-glycero-L-manno-non-2-ulosonic acid / pseudaminic acid (Pse)	Pse	101137651	252089088
5,7-Di-N-acetyl-pseudaminic acid	Pse5,7Ac₂	56927740	480493220	74, 75	[CSDB]
5,7-Di-N-acetyl-4-O-acetyl-pseudaminic acid	Pse4,5,7Ac₃	168009078	480493221	76	[CSDB]
5,7-Di-N-acetyl-8-O-acetyl-pseudaminic acid	Pse5,7,8Ac₃	168009079	480493222	75
5,7-Di-N-acetyl-8-O-glycyl-pseudaminic acid	Pse5,7Ac₂8Gly	168009080	480493223	77
5,7-Di-N-glyceryl-pseudaminic acid	Pse5,7Gr₂	168009081	480493224	75
5-N-Acetimidoyl-7-N-acetyl-pseudaminic acid	Pse7Ac5Am	168009082	480493225	75, 78	[CSDB]
5-N-Acetimidoyl-7-N-acetyl-8-O-acetyl-pseudaminic acid	Pse7,8Ac₂5Am	168009083	480493226	79
5-N-Acetimidoyl-7-N-acetyl-8-O-(N-acetyl-glutaminyl)-pseudaminic acid	Pse7Ac5Am8(Gln2Ac)	168009084	480493227	77
5-N-Acetyl-7-N-formyl-pseudaminic acid	Pse5Ac7Fo	163114430	480493228	80, 81	[CSDB]
5-N-Acetyl-7-N-L-glyceryl-pseudaminic acid	Pse5Ac7Gr	168009085	480493229	82
5-N-Acetyl-7-N-[(R)-3-hydroxybutyryl]-pseudaminic acid	Pse5Ac7(3_RHb)	168009086	480493230	80, 83, 84	[CSDB]
5-N-Acetyl-7-N-[(R)-3-hydroxybutyryl]-4-O-acetyl-pseudaminic acid	Pse4,5Ac₂7(3_RHb)	168009087	480493231	85, 86	[CSDB]
5-N-Acetyl-7-N-[(S)-3-hydroxybutyryl]-pseudaminic acid	Pse5Ac7(3_SHb)	168009088	480493232	84	[CSDB]
5-N-Acetyl-7-N-(4-hydroxybutyryl)-pseudaminic acid	Pse5Ac7(4Hb)	168009089	480493233	87	[CSDB]
5-N-Acetyl-7-N-(3,4-dihydroxybutyryl)-pseudaminic acid	Pse5Ac7(3,4Hb)	168009090	480493234	88	[CSDB]
7-N-Acetimidoyl-5-N-acetyl-pseudaminic acid	Pse5Ac7Am	168009091	480493235	89
5-N-Acetimidoyl-7-N-glyceryl-pseudaminic acid^a	Pse5Am7Gr	168009092	480493236	90	[CSDB]
7-N-Acetimidoyl-5-N-(2,3-di-O-methyl-glyceryl)-pseudaminic acid	Pse7Am5(Gr2,3Me₂)	168009093	480493237	91
7-N-Acetyl-5-N-(3-hydroxybutyryl)-pseudaminic acid	Pse7Ac5(3Hb)	168009094	480493238	92	[CSDB]
7-N-Acetyl-5-N-(2,3-di-O-methyl-glyceryl)-pseudaminic acid	Pse7Ac5(Gr2,3Me₂)	168009095	480493239	91
7-N-Formyl-5-N-[(R)-3-hydroxybutyryl]-pseudaminic acid	Pse7Fo5(3_RHb)	168009096	480493240	80, 93, 94	[CSDB]
5,7-Diamino-3,5,7,9-tetradeoxy-D-glycero-D-galacto-non-2-ulosonic acid / legionaminic acid (Leg)	Leg	70678967	252089090		[CSDB]
5,7-Di-N-acetyl-legionaminic acid^b	Leg5,7Ac₂	21572994	480493241	95, 96, 97, 98	[CSDB]
5,7-Di-N-acetyl-4-O-acetyl-legionaminic acid	Leg4,5,7Ac₃	168009097	480493242	76	[CSDB]
5,7-Di-N-acetyl-8-amino-8-deoxy-legionaminic acid	Leg5,7Ac₂8N	168009098	480493243	99	[CSDB]
5-N-Acetimidoyl-7-N-acetyl-legionaminic acid^b	Leg7Ac5Am	102086088	480493244	95, 97, 98	[CSDB]
5-N-Acetimidoyl-7-N-acetyl-8-O-acetyl-legionaminic acid^c	Leg7,8Ac₂5Am	168009099	480493245	95, 100	[CSDB]
5-N-Acetimidoyl-7-N-acetyl-5-N-methyl-legionaminic acid	Leg7Ac5Am5Me	168009100	480493246	101	[CSDB]
5-N-(N-Methyl-acetimidoyl)-7-N-acetyl-legionaminic acid	Leg7Ac5AmMe	168009101	480493247	97, 101	[CSDB]
5-N-(N,N-Dimethyl-acetimidoyl)-7-N-acetyl-legionaminic acid	Leg7Ac5AmMe₂	168009102	480493248	101
5-N-Acetimidoyl-7-N-acetyl-8-O-acetyl-5-N-methyl-legionaminic acid	Leg7,8Ac₂5Am5Me	168009103	480493249	100
5-N-(N,N-Dimethyl-acetimidoyl)-7-N-acetyl-8-O-acetyl-legionaminic acid	Leg7,8Ac₂5AmMe₂	168009104	480493250	100
5-N-Acetyl-7-N-(N-acetyl-D-alanyl)-legionaminic acid	Leg5Ac7(Ala2Ac)	10993159	480493251	96
5-N-Acetyl-7-N-(D-alanyl)-legionaminic acid	Leg5Ac7Ala	154573042	480493252	102	[CSDB]
7-N-Acetyl-5-N-formyl-legionaminic acid	Leg7Ac5Fo	168009105	480493253	103	[CSDB]
7-N-Acetyl-5-N-[(S)-3-hydroxybutyryl]-legionaminic acid^d	Leg7Ac5(3_SHb)	168009106	480493254	95, 98	[CSDB]
7-N-Acetyl-5-N-(N-methyl-5-glutamyl)-legionaminic acid	Leg7Ac5(5Glu2Me)	168009107	480493255	104
5,7-Diamino-3,5,7,9-tetradeoxy-D-glycero-D-talo-non-2-ulosonic acid / 4-epi-legionaminic acid (4eLeg)	4eLeg	126961780	252089092
5,7-Di-N-acetyl-4-epi-legionaminic acid	4eLeg5,7Ac₂	168009108	480493256	105, 98
5,7-Di-N-acetyl-8-O-acetyl-4-epi-legionaminic acid^e	4eLeg5,7,8Ac₃	168009109	480493257	95
5-N-Acetimidoyl-7-N-acetyl-4-epi-legionaminic acid	4eLeg7Ac5Am	168009110	480493258	106, 98
5-N-Acetimidoyl-7-N-acetyl-8-O-acetyl-4-epi-legionaminic acid	4eLeg7,8Ac₂5Am	168009111	480493259	106
5,7-Diamino-3,5,7,9-tetradeoxy-L-glycero-D-galacto-non-2-ulosonic acid / 8-epi-legionaminic acid (8eLeg)	8eLeg	168009112	252090150
5,7-Di-N-acetyl-8-epi-legionaminic acid^f	8eLeg5,7Ac₂	154573043	480493260	107, 108, 109, 98	[CSDB]
5,7-Di-N-acetyl-8-O-acetyl-8-epi-legionaminic acid	8eLeg5,7,8Ac₃	168009113	480493261	110	[CSDB]
5-N-Acetimidoyl-7-N-acetyl-8-epi-legionaminic acid	8eLeg7Ac5Am	168009114	480493262	111, 98	[CSDB]
7-N-Acetimidoyl-5-N-acetyl-8-epi-legionaminic acid	8eLeg5Ac7Am	168009115	480493263	67, 98
7-N-Acetimidoyl-5-N-acetyl-8-O-acetyl-8-epi-legionaminic acid	8eLeg5,8Ac₂7Am	168009116	480493264	67	[CSDB]
7-N-Acetyl-5-N-[(R)-3-hydroxybutyryl]-8-epi-legionaminic acid^f	8eLeg7Ac5(3_RHb)	168009117	480493265	95, 98	[CSDB]
7-N-Acetyl-5-N-(4-hydroxybutyryl)-8-epi-legionaminic acid^e	8eLeg7Ac5(4Hb)	168009118	480493266	95, 98	[CSDB]
5,7-Diamino-3,5,7,9-tetradeoxy-L-glycero-L-altro-non-2-ulosonic acid / acinetaminic acid (Aci)	Aci	126961779	252089094
5,7-Di-N-acetyl-acinetaminic acid	Aci5,7Ac₂	102515389	480493267	112	[CSDB]
5,7-Diamino-3,5,7,9-tetradeoxy-D-glycero-L-altro-non-2-ulosonic acid / 8-epi-acinetaminic acid (8eAci)	8eAci	168009119	480493268
5,7-Di-N-acetyl-8-epi-acinetaminic acid	8eAci5,7Ac₂	168009120	480493269	113	[CSDB]
Some related 9-deoxy-non-2-ulosonic acids
5- or 7-Acetamido-,7- or 5-(3-hydroxybutyramido)-5,7,9-trideoxy-non-2-ulosonic acid				114
5-Acetamido-7-[(S)-3-hydroxybutyramido]-8-amino-3,5,7,8,9-pentadeoxy-L-glycero-L-manno- or D-glycero-L-manno-non-2-ulosonic acid				115
5-Acetamidino-3,5,9-trideoxy-L-glycero-L-gluco-non-2-ulosonic acid (tentatively assigned chirality; trivial name: fusaminic acid)				116	[CSDB]
5-Acetamidino-4-O-acetyl-3,5,9-trideoxy-L-glycero-L-gluco-non-2-ulosonic acid (tentatively assigned chirality)				116	[CSDB]
5-Acetamidino-7-acetamido-3,5,7,9-tetradeoxy-D-glycero-L-gluco-non-2-ulosonic acid (tentatively assigned chirality)				117	[CSDB]