Preparation of high specific activity tritium labeled 6α,9,‐difluoro‐11β,21‐dihydroxy‐16α,17‐[(1‐methylethylidene)bis(oxy)]pregna‐1,4‐diene‐3,20‐one,fluocinolone acetonide

Fluocinolone acetonide was tritiated by selective reduction of the 1,2‐double bond of the O‐protected analog under tritium, followed by re‐establishment of the 1,2‐double bond and deprotection. Protection of both hydroxyl functionalities was required. The product was obtained with specific activity 36.8 Ci/mmol. Copyright © 2009 John Wiley & Sons, Ltd.     

De novo design of a pentameric coiled‐coil: decoding the motif for tetramer versus pentamer formation in water‐soluble phospholamban*

Abstract: Water‐soluble phospholamban (WSPLB) is a designed, water‐soluble analogue of the pentameric membrane protein phospholamban (PLB), which contains the same core and interhelical residues as PLB, with only the solvent‐exposed positions mutated. WSPLB contains the same secondary and quaternary structure as PLB. The hydrophobic cores of PLB and WSPLB contain Leu and Ile at the a ‐ and d ‐positions of a heptad repeat ( abcdefg ) from residues 31–52, while residues 21–30 are rich in polar amino acids at these positions. While the full‐length WSPLB forms pentamers in solution, truncated peptides lacking residues 21–30 are largely tetrameric. Thus, truncation of residues 1–20 promotes a switch from pentamer to tetramer formation. Here, the motifs for WSPLB pentamerization were elucidated by characterizing a series of peptides, which were progressively truncated in this polar ‘switch’ region. When fully present, the ‘switch’ region promotes pentamer formation in WSPLB, by destabilizing a more stable tetrameric species which exists in its absence. We find that the burial of hydrogen bonding residues from 21 to 30 drives WSPLB from a tetramer to a pentamer, with direct implications for coiled‐coil design.