The question whether the immunomodulating activity of rac-thalidomide
resides in either the (-)-(S)- or the (+)-(R)-enantiomer was addressed
by synthesis and separation of pure enantiomers of thalidomide-analog
ues which carry a methyl-group at the asymmetric carbon atom and are t
hus prevented from racemization. The effect of the pure enantiomers of
the thalidomide-analogues and also of the enantiomers of thalidomide
on release of TNF-alpha was tested in vitro by using stimulated periph
eral mononuclear blood cells. Both enantiomers of thalidomide inhibite
d the release of TNF-alpha equally well at low concentrations (5 and 1
2.5 mu g/ml) but at higher concentrations (25 and 50 mu g/ml) there wa
s a weak but statistically significant selectivity towards the (-)-(S)
-enantiomer. In the case of the configuration-stable thalidomide-analo
gues there was a very pronounced and statistically significant enantio
selectivity towards the (S)-form even at lower concentrations (greater
than or equal to 5 mu g/ml). The (S)-enantiomers of the thalidomide-a
nalogues differed in their inhibitory potency from (-)-(S)-thalidomide
suggesting that the introduction of the methyl-group increases the TN
F-alpha-inhibitory activity while the reduction of one of the carbonyl
-functions in the glutarimide-moiety to a methylene-group decreases ac
tivity. The effect of these small molecular alterations on activity an
d the enantioselectivity towards the (S)-enantiomers may indicate that
thalidomide and its analogues directly interact with one or several c
ellular target-proteins. (C) 1996 Wiley-Liss, Inc.