Fourteen derivatives of sparsomycin (1) were synthesized. Six of them were prepared following a novel synthetic route starting from the L-amino acid alanine. Some physicochemical properties, viz. lipophilicity and water solubility, of selected derivatives were measured. The biological activity was tested in vitro in cell-free protein synthesis inhibition assays, in bacterial and tumor cell growth inhibition assays, and in the L1210 leukemia in vivo model in mice. Also for selected drugs the acute toxicity in mice was determined. Ribosomes from both an eukaryotic and a prokaryotic organism were used in the protein synthesis inhibition systems. A linear correlation between the lipophilicity parameters measured was observed. Water solubility and drug toxicity in mice were found to be linearly correlated with lipophilicity. All the derivatives studied are more lipophilic than 1. The deshydroxysparsomycin analogues (30-33) showed an interesting phenomenon: increase in hydrophobicity was accompanied by a considerable increase in water solubility. We found that an increase in hydrophobicity of the drug as a result of replacing the SMe group of 1 with larger alkylthio groups causes an increase in the biological activity of the drug. However, not only the hydrophobicity but also shape and size of the substituent are important; in the homologous series 1-9-10-11-12, 21-22-23-24, and 30-31-32-33, highest protein synthesis inhibitory and in vitro cytostatic activity is found with compounds 11, 23, and 32, respectively, and in comparison with the highly active n-butyl compound 10, the isomeric tert-butyl compound 13 is rather inactive. Polar substituents replacing the SMe group, i.e. Cl in 17 and 35, also render the molecule inactive. Substituting the bivalent sulfur atom for a methylene group decreases the drug's activity. This effect can be compensated for by increasing the length of the alkylsulfinyl side chain. The agreement between the results derived from cell-free and "in vivo" tests is good. The assays using ribosomes of bacterial and eukaryotic organisms give similar results although the latter seem to be more sensitive to changes in hydrophobicity of the drug. Our results confirm the presence of a hydrophobic region at the peptidyl transferase center of the ribosome; the interaction of sparsomycin with this region is more pronounced in the eukaryotic particles. The sparsomycin analogues 11, 23, and 30 show the highest antitumor activity against L1210 leukemia in mice, their median T/C values are 386, 330, and 216%, respectively.(ABSTRACT TRUNCATED AT 400 WORDS)

N-pentyl-sparsomycin (PSm) is a lipophilic analogue of sparsomycin (Sm), which is a well known inhibitor of protein synthesis. This compound was selected for preclinical pharmacokinetic studies because of its high in vitro and in vivo antitumor activity. In this study in which the drug was evaluated in beagle dogs under anaesthesia, the drug concentrations in plasma, urine and bile samples were determined using high performance liquid chromatography (HPLC). Plasma protein binding was approximately 54%. The mean t1/2 beta was 0.2 hours (12 minutes) and t1/2 tau was 0.75 +/- 0.1 hours (45 +/- 6 minutes). During continuous infusions up to 5.25 hours, the steady state was reached in 3 out of 6 experiments, suggesting that in some cases the real t1/2 tau was longer than measured. PSm was actively reabsorbed from the renal tubuli. This process was saturable at the higher doses. Tubular reabsorption played only a minor role in pharmacokinetics as most of the drug (67%) was eliminated by the non-renal clearance. The non-renal clearance was saturable at higher doses of PSm and was the reason for non-linearity of pharmacokinetics.

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