Sperabillin B

A Gram-negative bacterium was found to produce new antibacterial antibiotics, sperabillins A, B, C and D, and the producing bacterium was characterized and identified as Pseudomonas fluorescens YK-437. Sperabillins were isolated by column chromatographies using cation-exchange resins, activated carbon and cation-exchange Sephadex, and preparative reverse-phase HPLC. Sperabillins showed antibacterial activity against Gram-negative and Gram-positive bacteria including antibiotic-resistant strains of Pseudomonas aeruginosa and Staphylococcus aureus. Sperabillin A inhibited DNA, RNA, protein, and cell wall biosynthesis in Escherichia coli. Sperabillins showed good protective effects in experimentally infected mice.

Diastereoselective conjugate addition of homochiral lithium (R)-N-allyl-N-alpha-methylbenzylamide to methyl (2E,5E)-hepatadienoate, followed by protecting group manipulation and subsequent iodocyclocarbamation allows a concise route to the core fragment, methyl (3R,5R,6R)-3,6-diamino-5-hydroxyheptanoate, of sperabillins B and D. Differentiation between the C-3 and C-6 primary amino groups of this core amino acid was readily achieved by treatment with acetone, giving the 5,6-isopropylidene and C-3-imine protected diamine, with subsequent regioselective acylation of the C-6-nitrogen facilitating the total synthesis of sperabillin D in 10.8% overall yield, and the first asymmetric synthesis of sperabillin B in 5.8% overall yield.

Modification of sperabillins was carried out. The 2-amidinoethylamino moiety was removed by brief acidic hydrolysis. The 2,4-hexadienoyl moiety was hydrogenated to the hexanoyl moiety and this was cleaved by an enzymatic reaction using the cells of Pseudomonas acidovorans IFO 13582. The 2-amidinoethylamino and the 2,4-hexadienoyl moieties were replaced with other groups. The derivative which was prepared by condensation of two molar amounts of dehexadienoylsperabillin A with (E,E)-muconic acid showed better protective effects than sperabillin A against Gram-negative bacteria.