Another Brick in the Wall of Tear Film Insights Added Through the Total Synthesis and Biophysical Profiling of anteiso-Branched Wax and Cholesteryl Esters.

ABSTRACT

The tear film lipid layer (TFLL) plays a vital part in maintenance of ocular health and represents a unique biological barrier comprising unusual and specialized lipid classes and species. The wax and cholesteryl esters (WEs and CEs) constitute roughly 80-90% of the TFLL. The majority of species in these lipid classes are branched and it is therefore surprising that the synthesis and properties of the second largest category of species, i.e., the anteiso-branched species, remain poorly characterized. In this study, we have developed a total synthesis route and completed a detailed NMR spectroscopic characterization of two common anteiso-branched species, namely (22S)-22-methyltetracosanyl oleate and cholesteryl (22'S)-22'-methyltetracosanoate. In addition, we have studied their structural properties in the bulk state by wide-angle and small-angle X-ray scattering and their behavior at the aqueous interface using Langmuir monolayer techniques. A comparison to the properties displayed by iso-branched and straight-chain analogues indicate that branching patterns lead to distinct properties in the CE and WE lipid classes. Overall, this study complements the previous work in the field and adds another important brick in the tear film insights wall.