Prenylation is critical for facilitating interactions between proteins and cell membranes. Most notably, prenylated proteins are involved in the cell division and replication cascade, making them useful targets for designing anti-cancer compounds. Prenylation, the transfer of either a 15 carbon or 20 carbon isoprenoid to the end of a protein with a specific CAAX box sequence, is catalyzed by the enzymes PFTase, PGGTase-I and PGGTase-II. By synthesizing non-natural analogues with bioorthogonal moieties, prenylated proteins can be identified and investigated. Reporter groups can be incorporated for post-prenylation modifications via site-specific click reactions allowing different functionalities to be installed. Here, efforts towards the synthesis of two alkyne-containing analogues are reported: a geranylgeranyl-diphosphate analogue with a propargyl moiety (C20 analogue) and a farnesyl-diphosphate analogue with a homopropargyl moiety (C15 analogue). These compounds were designed to serve as selective substrates for PGGTase-I and II. The C20 analogue (alcohol form) was assembled through a four-step sequence, including protection, oxidation, alkylation and deprotection. Metabolic labeling in HeLa cells followed by lysis, click reaction with TAMRA-azide and SDS PAGE analysis showed selective labeling of proteins in the 25 kDa MW range. Efforts to prepare the diphosphate form of that analogue and identify the labeled proteins are in progress. Work on the C15 analogue proved more difficult. While the protection and oxidations steps proceeded smoothly, efforts to alkylate the resulting alcohol at C-12 proved problematic. Although the work with the C15 analogue is currently inconclusive, results with the C20 compound suggest that this longer analogue could be useful for selective labeling of geranylgeranylated proteins.

Synthesis of new alkyne-containing geranylgeranyl diphosphate analogues

251st National Meeting (2016)

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