Leucomycin A1

The absolute bioavailability of oral spiramycin is generally within the range of 30 to 40%. After a 1 g oral dose, the maximum serum drug concentration was found to be within the range 0.4 to 1.4 mg/L. The tissue distribution of spiramycin is extensive. The volume of distribution is in excess of 300 L, and concentrations achieved in bone, muscle, respiratory tract and saliva exceed those found in serum. The intracellular penetration of spiramycin is also rapid and extensive, with the concentrations in alveolar macrophages 10 to 20 times greater than simultaneous serum concentrations. Spiramycin is less metabolised than some of the other macrolides. The renal excretion of spiramycin is low, with 4 to 20% of the dose being excreted by this route. High concentrations of spiramycin are achieved in bile, which is an important route of elimination. The serum elimination half-life of spiramycin is between 6.2 and 7.7 hours. Of significance to clinicians may be the finding that spiramycin is highly concentrated in the respiratory tract and other tissues and macrophages. The post-antibiotic effect of spiramycin is significant and this effect is more prolonged than that of erythromycin against Staphylococcus aureus. Spiramycin has also been shown to greatly reduce the capacity of strains of Gram-positive cocci to adhere to human buccal cells.

9-epi-Leucomycin A5 has been obtained from leucomycin A5 (I) by the following reaction sequence. Leucomycin A5 (I) was treated with Collins reagent (CrO3-pyridine) in the presence of water (13%) to provide 9-dehydroleucomycin A5 (II) in 95% yield. The formyl group was internally protected by the reaction of II with acetic anhydride-K2CO3 to afford 18,2'-di-O-acetyl-9-dehydroleucomycin A5-3,18-hemiacetal (III). Sodium borohydride reaction of II provided a 1 : 1 mixture of natural I and its 9-epimer, 9-epi-leucomycin A5 (IV), which were separated by silica gel chromatography. It was observed that the antimicrobial activities of both enantiomers were virtually identical with some tests strains but that of IV is reduced in comparison with I in some bacteria such as Staphylococcus epidermidis sp-al-1 and Streptococcus pyogenes N. Y. 5.

The biosynthesis of kitasamycin in Streptomyces kitasatoensis B-896 was profoundly influenced by the addition of precursors to complex and defined media: l-valine and l-leucine directed biosynthesis towards the pairs A(4)/A(5) (R(2) = butyryl) and A(1)/A(3) (R(2) = isovaleryl), respectively, and total kitasamycin titers were doubled and quadrupled, respectively. S. kitasatoensis B-896 was very resistant (>20 mg/ml) to alpha-aminobutyric acid, an analog of l-valine, but very susceptible to l-leucine analogs 5', 5', 5'-trifluoroleucine and 4-azaleucine (5 to 10 mug/ml). The inhibition by 4-azaleucine could be reversed by l-leucine, but by none of the other amino acids of the pyruvate family or the amino acids of the aspartate pathway. 4-Azaleucine-resistant mutants were isolated which in the absence of any precursors overproduced l-leucine and a kitasamycin complex mainly consisting of the pair A(1)/A(3). These 4-azaleucine-resistant mutants are presumed to be regulatory mutants in which alpha-isopropylmalate synthase, the first enzyme of the l-leucine pathway, has become either derepressed or desensitized to leucine feedback inhibition. l-Leucine-regulatory mutants have economic value: in the absence of expensive precursors, they produce a kitasamycin complex in which the most potent pair A(1)/A(3) is dominant and the least active components are absent.