Hypolipidemic activity of rifamycin derivatives.

Series of 3-piperidinyl- and 3-piperazinylrifamycins and to a certain extent 3-hydrazonorifamycins all bearing lipophilic side chains were found to exert potent hypolipidemic activity in lowering both serum cholesterol and LDL-cholesterol in rats. Starting from 3-[N'-(2,4,6-trimethylbenzyl)-N-piperazinyl]rifamycin SV (compound 25), a series of derivatives were synthesized with the aim of dissociating the hypolipidemic from the antibacterial activity, leading to the 8-O,N-dipivaloyl derivative of 25 (compound 48), which is devoid of any antibacterial activity but shows about 50-60% reduction of LDL-cholesterol and 20-30% reduction of serum cholesterol at a dose of 10 mg/kg. Compound 48 was selected for further pharmacological evaluation.

Sulfonylbenzoyl-nitrostyrenes: potential bisubstrate type inhibitors of the EGF-receptor tyrosine protein kinase.

The synthesis and biological activities of a series of sulfonylbenzoyl-nitrostyrene derivatives, a novel class of selective bisubstrate type inhibitors of the EGF-receptor tyrosine protein kinase, are described. The most potent derivatives inhibited the EGF-R tyrosine kinase, using angiotensin II as exogenous substrate, with IC50 values of less than or equal to 1 microM. No inhibition of the v-abl tyrosine kinase or the serine/threonine kinases PKC and PK-A was observed. In addition, active derivatives (compounds 5 and 12) effectively blocked the autophosphorylation of the EGF-R in vitro. Starting from the acids 5, 7, and 9, a series of esters, amides, and peptides was synthesized with the aim of increasing cellular penetration. Amides 14-18 showed potent antiproliferative effects using the EGF-dependent Balb/MK mouse epidermal keratinocyte cell line. Additionally, with the amide 14 inhibition of EGF-R autophosphorylation was demonstrated in the A431 cell line. CAMM studies using a computer-generated model for the transition state of the gamma-phosphoryl transfer from ATP to a tyrosine moiety and fitting experiments using the highly potent derivative 7 (IC50 value = 54 nM) support the hypothesis that the sulfonylbenzoyl group mimics a diphosphate moiety in the transition state. These results demonstrate that the rational design of tyrosine kinase inhibitors, using the inhibitory nitrostyrene moiety as a tyrosine mimic together with the sulfonylbenzoyl moiety as a diphosphate mimic, leads to highly potent and selective multisubstrate type inhibitors.

Dianilinophthalimides: potent and selective, ATP-competitive inhibitors of the EGF-receptor protein tyrosine kinase.

Dianilinophthalimides represent a novel class of inhibitors of the EGF-receptor protein tyrosine kinase with a high degree of selectivity versus other tyrosine and serine/threonine kinases. Steady-state kinetic analysis of compound 3, which showed potent inhibitory activity, revealed competitive type kinetics relative to ATP. Despite a highly symmetrical structure of compound 3, X-ray studies revealed an unsymmetrical propeller-shaped conformation of the molecule which differs clearly from that of the constitutionally related staurosporine aglycons. These conformational differences may explain the reversal of the selectivity profile of compound 3 relative to the staurosporine aglycons. In cellular assays compounds 3 and 4 have been shown to inhibit EGF-induced receptor autophosphorylation, c-fos induction and EGF-dependent proliferation of Balb/c MK cells. This inhibition was selective as compounds had no effect on PDGF-induced receptor autophosphorylation and c-fos induction. Furthermore, compound 3 showed potent antitumor activity in vivo at well-tolerated doses.

Semisynthetic bicyclomycin derivatives: preparation and antibacterial evaluation.

A number of semisynthetic bicyclomycin derivatives have been prepared by modifications at various sites of the molecule. The preparation, characterization and antimicrobial evaluation of the new compounds is described. In contrast to bicyclomycin itself, the new derivatives 48 and 58 are also active against Proteus species. Otherwise, the antibacterial potency of the bicyclomycin molecule was found to be very sensitive to structural changes.

CGP 4832, a new semisynthetic rifamycin derivative highly active against some gram-negative bacteria.

CGP 4832 (5) is a new derivative of rifamycin S, showing a very high degree of activity against certain Gram-negative bacteria, with MICs as much as 400 times lower than those of rifampicin. CGP 4832 and rifampicin inhibit DNA-dependent transcription in vitro to a similar extent, which excludes any difference in their effect on the target enzyme. The most plausible explanation for the potent activity of CGP 4832 is that it penetrates into bacterial cells by way of a specific mechanism. This hypothesis is corroborated by the high rate of mutations leading to bacterial strains resistant against CGP 4832.