Raymond Brambilla

The megalomicins. Part 7. A structural revision by carbon-13 nuclear magnetic resonance and X-ray crystallography. Synthesis and conformational analysis of 3-dimethylamino- and 3-azido-D- and -L-hexopyranosides, and the crystal structure of 4″-O-(4-lodobenzoyl)megalomicin A

An X-ray crystallographic study on 4″-O-(4-iodobenzoyl)megalomicin A has led to the revision of the structures of the megalomicins and the XK-41 antibiotics. Crystals are orthorhombic, space group P212121 with a= 12.669(2), b= 19.501 (6), c= 25.741 (9)A, and Z= 4. The structure was solved by the heavy-atom technique, and 1 812 observed reflections led to a final R of 0.095. The novel amino-sugar previously thought to be D-rhodosamine has been shown to have the L-configuration and is therefore renamed L-megosamine. It has also been shown to be glycosidically attached to the tertiary 6-hydroxy group. The 13C n.m.r. and circular dichroism (c.d.) parameters of these macrolides are described. The syntheses of methyl α- and β-D-rhodosaminide, methyl α- and β-D-megosaminide, methyl α- and β-L-megosaminide, methyl α- and β-D-angolosaminide, and methyl 2,3,6-trideoxy-3(dimethylamino)-α-D-xylo-hexopyranoside are described and their conformations and 13C n.m.r. parameters are discussed. Methyl α-D- and -L-amicetoside, methyl α-D- and -L-cineruloside and other model 4-oxopyranosides and pyrans have been synthesized. Their c.d. properties have been determined and they have been shown to exhibit Anti-Octant behaviour.

SCH 23831, a novel macrolide from Micromonospora rosaria

Abstract A novel macrolid elaborated by Micromonospora rosaria , SCH 23831, was assigned structure 2 on the basis of spectroscopic data. Several derivatives are also discussed.

Semisynthetic aminoglycoside antibacterials. Part 9. Synthesis of novel 1- and 3-substituted and 1- and 3-epi-substituted derivatives of sisomicin and gentamicin from the 1- and 3-oxo-derivatives

The conversion of selectively protected gentamicin and sisomicin derivatives into the 1- and 3-oxo-compounds by reaction with 3,5-di-t-butyl-1,2-benzoquinone is described. By application of suitable reductive techniques these oxo-aminoglycosides have been converted into novel 1- and 3-epi-, 1- and 3-deamino-1- and -3-hydroxy-, 1- and 3-deamino-1- and -3-epi-hydroxy-, and 1-deamino-derivatives. A study of the 13C n.m.r. parameters of the 1-epi- and 1-deamino-derivatives has led to the assignment of novel solution conformations for these new aminoglycosides.

Carbon-13 spin–lattice relaxation times of megalomicins, fourteen-membered macrolide antibiotics

Spin–lattice relaxation times and their application for spectral analysis of megalomicins are discussed. T1 Values of megalomicins and erythromycin are analysed in terms of molecular motions in solution.