The immunological properties of α(2→8) polysialic acid have been rationalized in terms of the presence of an epitope situated on a unique extended helical segment (n approximately 9) of the polymer. The critical importance of the carboxylate group to the stability of the extended helical epitope can be ascertained from NMR spectrocopic studies and potential energy calculations on the carboxyl reduced α(2→8) polysialic acid. These studies indicate that the extended helix (n approximately 9) is not stabilized in the reduced polymer and that the majority of conformers can only have helical parameters with n = 2 and 3. This result is also consistent with the fact that the reduced α(2→8) polysialic acid, contrary to its acidic counterpart, exhibits conventional immunological properties. Only five to six reduced oligomers are required to inhibit the binding of the reduced polysialic acid to its homologous antiserum. NMR spectroscopic analysis and potential energy calculations on the N-propionyl, N-butanoyl, N-isobutanoyl, N-pentanoyl, N-hexanoyl, and N-glycolyl derivatives of α(2→8) polysialic acid indicate that, despite the bulk of some of these substituents, they did not disrupt the extended helical conformer. The presence of the extended helical epitope in some of these N-acyl derivatives has also been confirmed from immunological data.

conformation, acid, epitope, neuraminic acid, derivative, reduced, comparison, polysialic acid, PDF, N-acyl

13C NMR data:
Linkage	Residue	C1	C2	C3	C4	C5	C6	C7	C8	C9
8,8,5	Ac	175.83	23.03
8,8	aXDD3dgalNonp5N-2-ulo	60.36	102.69	38.13	68.39	53.44	73.24	68.66	73.79	61.76
8,5	Ac	175.83	23.03
8	aXDD3dgalNonp5N-2-ulo	61.00	102.69	38.13	68.39	53.44	73.24	68.66	73.79	61.76
5	Ac	175.88	22.93
	aXDD3dgalNonp5N-2-ulo	68.18	97.98	37.88	67.87	53.44	70.82	68.95	73.06	62.75


1H NMR data:
Linkage	Residue	H1	H2	H3	H4	H5	H6	H7	H8	H9
8,8,5	Ac	-	2.054
8,8	aXDD3dgalNonp5N-2-ulo	3.814-3.914	-	1.701-2.314	3.923	3.856	3.692	3.570	3.719	3.643-3.844
8,5	Ac	-	2.046
8	aXDD3dgalNonp5N-2-ulo	3.750-3.792	-	1.701-2.448	3.861	3.861	3.715	3.747	4.153	3.758-3.973
5	Ac	-	2.046
	aXDD3dgalNonp5N-2-ulo	3.534-3.534	-	1.678-2.087	4.027	3.843	3.960	3.751	4.132	3.766-3.917


1H/13C HSQC data:
Linkage	Residue	C1/H1	C2/H2	C3/H3	C4/H4	C5/H5	C6/H6	C7/H7	C8/H8	C9/H9
8,8,5	Ac		23.03/2.054
8,8	aXDD3dgalNonp5N-2-ulo	60.36/3.814-3.914		38.13/1.701-2.314	68.39/3.923	53.44/3.856	73.24/3.692	68.66/3.570	73.79/3.719	61.76/3.643-3.844
8,5	Ac		23.03/2.046
8	aXDD3dgalNonp5N-2-ulo	61.00/3.750-3.792		38.13/1.701-2.448	68.39/3.861	53.44/3.861	73.24/3.715	68.66/3.747	73.79/4.153	61.76/3.758-3.973
5	Ac		22.93/2.046
	aXDD3dgalNonp5N-2-ulo	68.18/3.534-3.534		37.88/1.678-2.087	67.87/4.027	53.44/3.843	70.82/3.960	68.95/3.751	73.06/4.132	62.75/3.766-3.917

There is only one chemically distinct structure:

SVGMWSMILES3D molIonize

 

CC(=O)N[C@@H]1[C@@H](O)C[C@@](O)(CO)O[C@H]1[C@H](O)[C@@H](CO)O[C@@]1(CO)C[C@H](O)[C@@H](NC(C)=O)[C@H]([C@H](O)[C@@H](CO)O[C@@]2(CO)C[C@H](O)[C@@H](NC(C)=O)[C@H]([C@H](O)[C@H](O)CO)O2)O1

849.834 g/mol (C₃₃H₅₉N₃O₂₂)