DETERMINATION OF THE ANTI-FACTOR Xa ACTIVITY OF THE SYNTHETIC PENTASACCHARIDE SR 90107A/ORG 31540 AND OF TWO STRUCTURAL ANALOGUES

The anti-factor Xa activity of the synthetic pentasaccharide SR 90107A/ORG 31540 was assayed by a chromogenic method at pH 8.4 and pH 7.35, comparatively to the 4 th International Heparin Standard (IHS) or to the I st International Low Molecular Weight Heparin Standard (LMWHS). At pH 8.4, SR 90107A/ORG 31540 was found to have a specific anti-factor Xa activity of 639 ± 14 and 659 ± 19 IU/mg (mean ± sem, n=6) when assayed in comparison with the 4 th ISH and the I st LMWHS respectively. At pH 7.35, the corresponding figures were 864 ± 6 and 1160 ± 51 IU/mg (mean ± sem, n=6) respectively. The dissociation constants of the ATIII-pentasaccharide complex formed by SR 90107A/ORG 31540 and by two close analogues: SR 80327A and SR 80027A in the presence of purified human ATIII were found to be 41 ± 8, 96 ± 1 and 3 ± 1.4 nM (mean ± sem, n=3) respectively. For the three compounds, the pseudo-first order molar catalytic constants for factor Xa inactivation by the ATIII-pentasaccharide complex were shown to be statistically comparable, in the range of 7–8 × 10 7 min −1 per mole. It is concluded that the differences in specific anti-factor Xa activities between SR 90107A/ORG 31540 and its synthetic chemical analogues can be attributed to variations of the dissociation constants whereas the catalytic constants for factor Xa inactivation remain unchanged. Copyright © 1997 Elsevier Science Ltd