[Structure of the aglycones of mycosides A and B]

Astonishing diversity of natural surfactants: 3. Carotenoid glycosides and isoprenoid glycolipids

Carotenoid glycosides and isoprenoid glycolipids are of great interest, especially for the medicinal, pharmaceutical, food, cosmetic, flavor, and fragrance industries. These biologically active natural surfactants have good prospects for the future chemical preparation of compounds useful as antimicrobial, antibacterial, and antitumor agents, or in industry. More than 300 unusual natural surfactants are described in this review article, including their chemical structures and biological activities.

The dimycocerosate ester polyketide virulence factors of mycobacteria

Recent advances in the study of mycobacterial lipids indicate that the class of outer membrane lipids known as dimycocerosate esters (DIMs) are major virulence factors of clinically relevant mycobacteria including Mycobacterium tuberculosis and Mycobacterium leprae. DIMs are a structurally intriguing class of polyketide synthase-derived wax esters discovered over seventy years ago, yet, little was known until recently about their biosynthesis. Availability of several mycobacterial genomes has accelerated progress toward clarifying steps in the DIM biosynthetic pathway and it is our belief that reviewing the bases of our current knowledge will clarify outstanding issues and help direct future endeavors.

Synthesis of methyl 2,4-di-O-methyl-3-O-(2-O-methyl-alpha-L-rhamnopyranosyl)-alpha-L- rhamnopyranoside and methyl 2,4-di-O-methyl-3-O-[2-O-methyl-3-O-(2-O-methyl-alpha-L-fucopyranosyl)- alpha-L-rhamnopyranosyl]-alpha-L-rhamnopyranoside: di- and tri-saccharide segments of a phenolic glycolipid of Mycobacterium kansasii

Syntheses of the title glycosides are described. The critical O-glycosylations were carried out in the presence of boron trifluoride etherate with a high degree of alpha-selectivity.

The carbohydrate- and lipid-containing cell wall of mycobacteria, phenolic glycolipids: structure and immunological properties

Phenolic glycolipids were first discovered as cell-wall constituents of M. bovis, M. bovis BCG, M. marinum, and M. kansasii. Recently, such compounds were also isolated from M. leprae and have been shown to be specific-species serological markers. Moreover, they seem to be involved, in the case of lepromatous leprosy, in the stimulation of the suppressor T-cells. The functional activities of these phenolic glycolipids over the immune cells stimulation emphasized the role played by these molecules in the mycobacteria pathogenicity. Phenolic glycolipids have also been found in M. gastri and M. tuberculosis strain Canetti. From a structural point of view, these glycolipids contain the same aglycon moiety mainly assigned to phenolphthiocerol diester while the sugar part structure confers to some of these glycolipids their antigenic specificity. The search of immunoreactive glycolipids and their function analysis remain a challenge for chemists and immunologists for the understanding of the mycobacteria pathogenicity.

Specificity of a Mycobacterium kansasii phenolic glycolipid (mycoside A) immunoserum

The specificity of Mycobacterium kansasii anti-mycoside A antiserum prepared in rabbits injected with purified samples of the phenolic glycolipid was evaluated by an enzyme-linked immunosorbent assay. Chloroform-methanol extracts from representative strains of 23 mycobacterial species and 50 strains of M. kansasii showed that all strains of M. kansasii and the representative strain of M. gastri formed the antigen, whereas none of the remaining species (including M. leprae) formed it. Consequently, it was found that the antiserum was highly specific and useful for diagnostic purposes.

Absolute configuration of the unique 2,6-dideoxy-4-O-methyl-arabino-hexopyranose of the major phenolic glycolipid antigen from Mycobacterium kansasii

The antigenicity and the structure of the major phenolic glycolipid from Mycobacterium kansasii have been established. A monoacetylated tetrasaccharide structure was proposed for the oligosaccharide moiety in which the distal sugar, unique in nature, corresponds to 2,6-dideoxy-4-O-methyl-alpha-arabinohexopyranose. Its terminal position in the oligosaccharide part confers to this residue a key role in the antigen-antibody interaction. By improvement of the methanolysis procedure, this new kind of sugar was obtained in higher amounts than by hydrolysis of the glycolipid. Its 1H-NMR spectrum is presented and its optical rotatory power measurement agrees with a D absolute configuration while the deoxyhexoses involved in the glycolipid tetrasaccharide structure present the L absolute configuration.

Lipids of putative relevance to virulence in Mycobacterium tuberculosis: phthiocerol dimycocerosate and the attenuation indicator lipid

Lipid compositions of 40 patient isolates of Mycobacterium tuberculosis derived from Madras, Burma, Rangoon, and East Africa were studied, and two major populations of tubercle bacilli were distinguished. Nearly all of the strains previously designated as attenuated for the guinea pig (D. A. Mitchison) are characterized by a specific phenolic phthiocerol diester which is identified with the aglycone moieties of mycosides A and B (and probably G). This lipid (AI) was not seen in any of the more virulent strains. Thus, presence of AI may be taken as definitive for attenuation (P << 0.001). Phthiocerol dimycoserosate (DIM), a companion substance, is ubiquitous for the series of 40 strains. However, a dramatic attenuation found in a DIM-less H37Rv mutant may support a role for this substance in the virulent state. Since mycosides A, G, and B seem to be restricted to certain chromogenic and bovine species, respectively, we speculate that lysogenization or transduction of fully virulent M. tuberculosis may have provided the genetic determinants for attenuation and AI synthesis, and thus led to the two classes of tubercle bacilli.