Phase Behaviour of Cord Factor and Related Bacterial Glycolipid Toxins

C‐6 esters of methyl α‐ D ‐glucoside and C‐6, C‐6′ diesters of α,α′‐ D ‐trehalose with C 18 and C 32 threo and erythro mycolic acids (from chemical source) and of C 80 ‐ erythro ‐mycolic acid (from natural source) have been synthesized. Esters of a C 32 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 C 32 esters suggested a transition between liquid‐expanded and liquid‐condensed 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(C 32 ‐ erythro ‐mycoloyl)‐trehalose. On the other hand, short chain C 18 esters form fluid phases ( t > 10°C) whereas very long chain C 80 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.