DETERMINATION OF THE ANTI-FACTOR XA ACTIVITY OF THE SYNTHETIC PENTASACCHARIDE SR-90107A ORG-31540 AND OF 2 STRUCTURAL ANALOGS

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 1(st) International Low Molecular Weight Heparin Standard (LMWHS). At pH 8.4, SR 90107A/ORG 31540 was found to have a specific anti-fact or Xa activity of 639+/-14 and 659+/-19 IU/mg (mean+/-sem, n=6) when a ssayed in comparison with the 4(th) ISH and the 1(st) LMWHS respective ly. At pH 7.35, the corresponding figures were 864+/-6 and 1160+/-51 I U/mg (mean+/-sem, n=6) respectively. The dissociation constants of the ATIII-pentasaccharide complex formed by SR 90107A/ORG 31540 and by tw o 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+/-se m, n=3) respectively. For the three compounds, the pseudo-first order molar catalytic constants for factor Xa inactivation by the ATIII-pent asaccharide complex were shown to be statistically comparable, in the range of 7-8x10(7) min(-1) per mole. It is concluded that the differen ces in specific anti-factor Xa activities between SR 90107A/ORG 31540 and its synthetic chemical analogues can be attributed to variations o f the dissociation constants whereas the catalytic constants for facto r Xa inactivation remain unchanged. Copyright (C) 1997 Elsevier Scienc e Ltd.