Phase Behavior of Cord Factor and Related Bacterial Glycolipid Toxins.

C-6 esters of methyl α-D-glucoside and C-6, C-6' diesters of α,a'-D-trehalose with C₁₈ and C₃₂ threo and erythro mycolic acids (from chemical source) and of C₈₀-erythro-mycolic acid(from natural source) have been synthesized. Esters of a C₃₂ deoxy analogue were prepared as well. Throughout a monolayer study at the air-water interface, these glycolipids are shown to form well organized phases in which the two hydrocarbon chains of mycoloyl residues must be in interaction. Compression isotherms of C₃₂ esters suggested a transition between liquid-expanded and liquidcondensed states. Latent heats Q_c and entropy changes Δ S associated with these phase transitions as well as the critical temperature at which they occur have been measured. Within the monolayer, the molecular packing of these glycolipids depends on the presence of the hydroxyl group of mycoloyl residues and on its stereochemistry. In particular, intermolecular hydrogen bonds between these groups are postulated in the case of the bis(C₃₂-erythro-mycoloyl)-trehalose. On the other hand, short chain C₁₈ esters form fluid phases (t > 10°C) whereas very long chain C₈₀ mycoloyl esters of trehalose exist in a condensed state (t = 20 °C). These glycolipids were found to interact strongly with dipalmitoylphosphatidylcholine and egg yolk lecithins (3-sn-phosphatidylcholine). Their phase behaviours are discussed in connection with hypotheses concerning the way they can interact with mitochondrial membranes. [ABSTRACT FROM AUTHOR]