(E)-4-Hydroxy-3-methyl-but-2-enyl diphosphate (HMBPP) and its phosphonate analogs are potent phosphoantigens. HMBPP contains an (E)-allylic alcohol which interacts with the molecular target BTN3A1 giving an antigenic signal to activate Vγ9Vδ2 T cells. As probes of BTN3A1 function, we prepared prodrug derivatives of the HMBPP analog C-HMBP that lack the (E)-allylic alcohol or have modified it to an aldehyde or aldoxime and evaluated their biological activity. Removal of the alcohol completely abrogates phosphoantigenicity in these compounds while the aldoxime modification decreases potency relative to the (E)-allylic alcohol form. However, homoprenyl derivatives oxidized to an aldehyde stimulate Vγ9Vδ2 T cells at nanomolar concentrations. Selection of phosphonate protecting groups (i.e., prodrug forms) impacts the potency of phosphoantigen aldehydes, with mixed aryl acyloxyalkyl forms exhibiting superior activity relative to aryl amidate forms. The activity correlates with the cellular reduction of the aldehyde to the alcohol form. Thus, the functionality on this ligand framework can be altered concurrently with phosphonate protection to promote cellular transformation to highly potent phosphoantigens.

No abstract

The natural schweinfurthins are stilbenes with significant antiproliferative activity and an uncertain mechanism of action. To obtain a fluorescent analogue with minimal deviation from the natural structure, a coumarin ring system was annulated to the D-ring, creating a new analogue of schweinfurthin F. This stilbene was prepared through a convergent synthesis, with a Horner–Wadsworth–Emmons condensation employed to form the central stilbene olefin. After preparation of a tricyclic phosphonate via a recent and more efficient modification of the classic Arbuzov reaction, condensation was attempted with an appropriately substituted bicyclic aldehyde but the coumarin system did not survive the reaction conditions. When olefin formation preceded generation of the coumarin, the stilbene formation proceeded smoothly and ultimately allowed access to the targeted coumarin-based schweinfurthin analogue. This analogue displayed the desired fluorescence properties along with significant biological activity in the National Cancer Institute’s 60-cell line bioassay, and the pattern of this biological activity mirrored that of the natural product schweinfurthin F. This approach gives facile access to new fluorescent analogues of the natural schweinfurthins and should be applicable to other natural stilbenes as well.