Conformationally constrained analogues of diacylglycerol (DAG). 3. Interaction of α-alkyl-γ-lactones with protein kinase C (PK-C)

Enantioselective Syntheses of 2-Deoxyxylono-1,4-lactone and 2-Deoxyribono-1,4-lactone from 1,3-Dioxan-5-yl Diazoacetates

1,3-Dioxan-5-yl diazoacetates are valuable substrates for highly diastereoselective and enantioselective carbon-hydrogen insertion reactions. trans-2-(tert-Butyl)-1,3-dioxan-5-yl diazoacetate is a direct precursor to 2-deoxyribono-1,4-lactone in up to 81% ee, whereas cis-2-(tert-butyl)-1,3-dioxan-5-yl diazoacetate yields only the protected 2-deoxyxylono-1,4-lactone in up to 96% ee. However, trans-2-aryl-1,3-dioxan-5-yl diazoacetate (aryl = phenyl or 2-naphthyl) forms the precursor to 2-deoxyxylono-1,4-lactone in up to 95% ee but with the mirror image configuration of that produced from the trans-2-(tert-butyl) analogue. The catalysts that are most suitable for these carbon-hydrogen insertion reactions are chiral dirhodium(II) carboxamidates. 1,3-Dialkoxy-2-propyl diazoacetates give mainly 2-deoxyxylono-1,4-lactone derivatives (>90:10) with generally high enantiocontrol, but replacement of hydrogen at the 2-position of these 2-propyl diazoacetates led to a mixture of products.

beta2-chimaerin is a novel target for diacylglycerol: binding properties and changes in subcellular localization mediated by ligand binding to its C1 domain

The members of the chimaerin family of Rac-GTPase-activating proteins possess a single C1 domain with high homology to those present in protein kinase C (PKC) isozymes. This domain in PKCs is involved in phorbol ester and diacylglycerol (DAG) binding. We previously have demonstrated that one of the chimaerin isoforms, beta2-chimaerin, binds phorbol esters with high affinity. In this study we analyzed the properties of beta2-chimaerin as a DAG receptor by using a series of conformationally constrained cyclic DAG analogues (DAG lactones) as probes. We identified analogs that bind to beta2-chimaerin with more than 100-fold higher affinity than 1-oleoyl-2-acetylglycerol. The potencies of these analogs approach those of the potent phorbol ester tumor promoters. The different DAG lactones show some selectivity for this novel receptor compared with PKCalpha. Cellular studies revealed that these DAG analogs induce translocation of beta2-chimaerin from cytosolic (soluble) to particulate fractions. Using green fluorescent protein-fusion proteins for beta2-chimaerin we determined that this novel receptor translocates to the perinuclear region after treatment with DAG lactones. Binding and translocation were prevented by mutation of the conserved Cys-246 in the C1 domain. The structural homology between the C1 domain of beta2-chimaerin and the C1b domain of PKCdelta also was confirmed by modeling analysis. Our results demonstrate that beta2-chimaerin is a high affinity receptor for DAG through binding to its C1 domain and supports the emerging concept that multiple pathways transduce signaling through DAG and the phorbol esters.

The transition from a pharmacophore-guided approach to a receptor-guided approach in the design of potent protein kinase C ligands

The pharmacophore-guided approach used in the first phase of the design of novel protein kinase C (PKC) ligands was based on the study of the geometry of bioequivalent pharmacophores present in diacylglycerol (DAG) and in the more potent phorbol ester tumor promoters. A number of potent DAG lactones were generated by this approach, in which the glycerol backbone was constrained into various heterocyclic rings to reduce the entropic penalty associated with DAG binding. Based on the information provided by X-ray and NMR structures of the cysteine-rich, C1 phorbol ester/DAG binding domain, the DAG lactones were further modified to optimize their interaction with a group of highly conserved hydrophobic amino acids along the rim of the C1 domain. This receptor-guided approach culminated with the synthesis of a series of "super DAG" molecules that can bind to PKC with low nanomolar affinities. These compounds provide insight into the basis for PKC ligand specificity. Moreover, some of the compounds reviewed herein show potential utility as antitumor agents.