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
8,5	Ac	175.77	23.00
8	aXDD3dgalNonp5N-2-ulo	60.85	102.18	38.80	68.75	53.06	72.76	68.05	71.79	63.89
5	Ac	175.89	22.92
	aXDD3dgalNonp5N-2-ulo	68.09	97.98	38.06	67.87	53.49	70.76	69.06	73.46	62.30


1H NMR data:
Linkage	Residue	H1	H2	H3	H4	H5	H6	H7	H8	H9
8,5	Ac	-	2.043
8	aXDD3dgalNonp5N-2-ulo	3.762-3.875	-	1.735-2.334	3.905	3.841	3.680	3.560	3.739	3.630-3.838
5	Ac	-	2.056
	aXDD3dgalNonp5N-2-ulo	3.540-3.540	-	1.704-2.077	4.030	3.830	3.960	3.767	4.162	3.758-3.933


1H/13C HSQC data:
Linkage	Residue	C1/H1	C2/H2	C3/H3	C4/H4	C5/H5	C6/H6	C7/H7	C8/H8	C9/H9
8,5	Ac		23.00/2.043
8	aXDD3dgalNonp5N-2-ulo	60.85/3.762-3.875		38.80/1.735-2.334	68.75/3.905	53.06/3.841	72.76/3.680	68.05/3.560	71.79/3.739	63.89/3.630-3.838
5	Ac		22.92/2.056
	aXDD3dgalNonp5N-2-ulo	68.09/3.540-3.540		38.06/1.704-2.077	67.87/4.030	53.49/3.830	70.76/3.960	69.06/3.767	73.46/4.162	62.30/3.758-3.933

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](O)CO)O1

572.561 g/mol (C₂₂H₄₀N₂O₁₅)