Synthesis and properties of methyl 5-(1'R,2'S)-(2-octadecylcycloprop-1-yl)pentanoate and other omega-19 chiral cyclopropane fatty acids and esters related to mycobacterial mycolic acids

Synthesis of 13 C-labelled ω-hydroxy carboxylic acids of the general formula HO2 13 C-(CH2 )n -CH2 OH or HO2 C-(CH2 )n -13 CH2 OH (n = 12, 16, 20, 28)

¹³ C-labelled ω-hydroxy-carboxylic acids HO₂ ¹³ C-(CH₂ )_n -CH₂ OH or HO₂ C-(CH₂ )_n -¹³ CH₂ OH (n = 12, 16, 20, 28) with ¹³ C labels selectively introduced either at the carboxy group or at the primary alcohol function at the end of the hydrocarbon chain have been synthesized. Different synthetic strategies had to be applied depending on the position of the label, the chain length of the respective synthetic target and due to economic considerations. ¹³ C labels in general were introduced by nucleophilic substitution of a suitable leaving group with labelled potassium cyanide and subsequent hydrolysis of the nitriles to produce the corresponding labelled carboxy functions, which may also be reduced to give the labelled primary alcohol group. All new compounds are characterized by GC/MS, IR and NMR methods as well as by elemental analysis.

Synthesis of 13 C-labelled cutin and suberin monomeric dicarboxylic acids of the general formula HO2 13 C-(CH2 )n -13 CO2 H (n = 10, 12, 14, 16, 18, 20, 22, 24, 26, 28)

¹³ C-labeled dicarboxylic acids HO₂ ¹³ C-(CH₂ )_n -¹³ CO₂ H (n = 10, 12, 14, 16, 18, 20, 22, 24, 26, 28) have been synthesized as internal standards for LC-MS and GC-MS analysis of cutin and suberin monomer degradation by soil-based microorganisms. Different synthetic strategies had to be applied depending on the chain length of the respective synthetic target and because of economic considerations. ¹³ C-labels were introduced by nucleophilic substitution of a suitable leaving group with labelled potassium cyanide and subsequent hydrolysis of the nitriles to produce the corresponding dicarboxylic acids. All new compounds are characterized by GC/MS, IR, and NMR methods as well as by elemental analysis.

Synthesis of trehalose glycolipids

Chemical synthesis of trehalose glycolipids such as DAT, TDM, SL-1, SL-3, and Ac₂SGL from MTb, emmyguyacins from fungi, succinoyl trehalose from rhodococcus, and maradolipids from worms, as well as mycobacterial oligosaccharides is reviewed.

Total Synthesis of an Immunogenic Trehalose Phospholipid from Salmonella Typhi and Elucidation of Its sn-Regiochemistry by Mass Spectrometry

Diphosphatidyltrehalose (diPT) is an immunogenic glycolipid, recently isolated from Salmonella Typhi. Despite rigorous structure elucidation, the sn-position of the acyl chains on the glycerol backbone had not been unequivocally established. A stereoselective synthesis of diPT and its regioisomer is reported herein. Using a hybrid MS³ approach combining collisional dissociation and ultraviolet photodissociation mass spectrometry for analysis of the regioisomers and natural diPT, the regiochemistry of the acyl chains of this abundant immunostimulatory glycolipid was established.

Molecular structure of the Mycobacterium tuberculosis virulence factor, mycolic acid, determines the elicited inflammatory pattern

Mycolic acids (MAs) occur in the cell wall of Mycobacterium tuberculosis as variable mixtures of different classes and chain lengths. Here, we address the relationship between the structure and its inflammatory function of this virulence factor using single synthetic MA isomers, differing in oxygenation class and cis- versus α-methyl-trans proximal cyclopropane orientation. Analysis of bronchoalveolar inflammation, lung histopathology and alveolar macrophage transcription revealed a strong dependence on these meromycolic chemistries of mouse pulmonary inflammation in response to intratracheal treatments with MAs. Whereas α-MA was inert, oxygenated methoxy- and keto-MA with cis-cyclopropane stereochemistry elicited solid to mild inflammatory responses respectively. In trans-cyclopropane orientation, methoxy-MA partially lost its inflammatory activity and keto-MA exerted anti-inflammatory alternative activation of alveolar macrophages and counteracted cis-methoxy-MA induced airway inflammation. The differential innate immune activities of MAs demonstrated here, dependent on oxygenation class and cis versus α-methyl-trans cyclopropane chemistry, identify a novel means for M. tuberculosis to steer host immune responses during infection.