Analogs of the potent inhibitor of glucosylceramide (GlcCer) synthase, D-th
reo-1-phenyl-2-palmitoylamino-3-pyrrolidino-1-propanol (P4), based on subst
itutions in the palmitoyl group were made by means of a stereo-selective sy
nthetic method in order to elucidate the role of the hydrophobic portion in
both the inhibitory action toward the enzyme and the biological effects. W
hile P4 strongly inhibited GlcCer synthase with an IC50 of 0.5 mu M in vitr
o, it also inhibited cell growth by 50% at the concentration of 7 mu M, The
shorter N-acyl chain analogs including decanoyl, octanoyl, and hexanoyl gr
oups showed similar IC50 values for GlcCer synthase (around 2 mu M), but th
e hexanoyl analog exhibited only a slight inhibitory effect on cell growth,
showing the dissociation between GlcCer depletion and cell growth. Several
compounds which exhibit similar hydrophobicity to the hexanoyl analog of P
4 were subsequently designed. We found that D-threo-1-phenyl-abenzyloxycarb
onylamino-3-pyrrolidino-1-propanol (PBPP) was a most potent inhibitor, show
ing an IC50 of 0.3 mu M. In cultured cells, PBPP was able to deplete glycos
phingolipids without affecting cell growth or the ceramide level.