The formal total synthesis of trehazolin based on pyridinium salt photochemistry and identification of the physiological function of petal death protein

The work described in this dissertation focuses on the formal total synthesis of trehazolin based on pyridinium salt photochemistry and identification of the physiological function of the petal death protein.; The first effort focused on the development of a strategy for the synthesis of trehazolamine, the aminocyclitol core of the potent trehalase inhibitor trehazolin, that is based on pyrydinium salt photochemistry. The methodology takes advantage of photocyclization reaction of 1-methoxyethoxymethyl-3-pivaloxymethylpyridinium perchlorate to generate a bicyclic-aziridine intermediate, which is transformed under aziridine ring opening conditions to the key intermediate, 3,5-diacetoxy-3-pivaloxymethyl-4-(N-acetylamino)cyclopentene. In addition, the strategy is used in an enantio-divergent sequence for preparation of the natural (+)-trehazolamine and its unnatural (-)-enantiomer. In this route, the chiral auxiliary containing, 1-(tetracetyl-alpha-D-glucosyl)-3-pivaloxymethylpyridinium perchlorate undergoes photocyclization to generate separable, diastereomeric bicyclic-aziridines, which are then independently transformed to enantiomeric 3,5-diacetoxy-3-pivaloxymethyl-4-(N-acetylamino)-cyclopentenes.; The second area described in Part II of the dissertation research involved studies conducted to define the chemical function of the petal death protein, a Dianthus caryophyllus protein that is a member of the isocitrate lyase (ICL) family. This protein (Swiss-Prot entry Q05957) is synthesized in the senescent flower petals and is named the "petal death protein" or "PDP". Based on an analysis of the structural contexts of sequence markers common to the C-C bond lyases of the isocitrate lyase/phosphoenolpyruvate mutase superfamily, a substrate screen that employed a 2R-malate core structure was designed. Accordingly, stereochemically defined C(2) and C(3) substituted malates were synthesized and tested as substrates for PDP catalyzed C(2)-C(3) bond cleavage. The screen identified 2R-ethyl-3S-methylmalate and oxaloacetate as the most active substrates (for each kcat/Km = 2 x 104 M-1 s-1). It is hypothesized that PDP functions in oxalate production for Ca2+ sequestering and/or in carbon scavenging from alpha-hydroxycarboxylate catabolites during the biochemical transition accompanying petal senescence.