The efficient synthesis of enantiopure, trisubstituted cryptophane-A derivatives, organic host molecules with unusually high xenon affinity is reported. Synthesis and chromatographic separation of (+/−) tri-Mosher’s acid-substituted cryptophane diastereomers gave ready access to the enantiopure cryptophanes, which are critical components in the design of enantiomerically pure 129Xe biosensors. Hyperpolarized 129Xe NMR spectroscopy identified single resonances for both trisubstituted cryptophane diastereomers that were separated by 9.5 ppm. This highlights opportunities for using enantiopure xenon biosensors in the simultaneous detection of 129Xe in different biochemical environments.

A novel fluorine-18 prosthetic ligand, 5-(1,3-dioxolan-2-yl)-2-(2-(2-(2- fluoroethoxy)ethoxy)ethoxy)pyridine [18F]2, has been synthesized. The prosthetic ligand is formed in high radiochemical yield (rcy = 71 ± 2 %, n = 3) with excellent radiochemical purity (rcp = 99 ± 1 %, n = 3) in a short reaction time (10 min). [18F]2 is a small, neutral, organic complex, easily synthesized in four steps from a readily available starting material. It can be anchored onto a target molecule containing an aminooxy functional group under acidic conditions by way of an oxime bond. We report herein two examples [18F]23 and [18F]24, potential imaging agents for β-amyloid plaques, which were labeled with this prosthetic group. This approach could be used for labeling proteins and peptides containing an aminooxy group. Biodistribution in male ICR mice for both oxime labeled complexes [18F]23 and [18F]24 were compared to that of the known β-amyloid plaque indicator, [18F]-AV-45, florbetapir 1. Oximes [18F]23 and [18F]24 are larger in size and therefore should reduce the blood-brain barrier (BBB) penetration. The brain uptake for oxime [18F]23 appeared to be reduced, but still retained some capability to cross the BBB. Oxime [18F]24 showed promising results after 2 min post injection (0.48 % dose/gram), however the uptake increased after 30 min post injection (0.92 % dose/gram) suggesting an in-vivo decomposition/metabolism of compound [18F]24. We have demonstrated a general protocol for the fluoride-18 labeling with a new prosthetic ligand [18F]2 that is tolerant towards several functional groups and is formed via chemoselective oxime coupling.

Microwave-assisted solid-phase syntheses of six "difficult" peptides, H-VVSVV-NH(2) (3), H-VVVSVV-NH(2) (4), H-VIVIG-OH (5), H-TVTVTV-NH(2) (6), H-VKDGYI-NH(2) (7), and H-VKDVYI-NH(2) (8), were achieved utilizing N-(Fmoc-alpha-aminoacyl)benzotriazoles. Extension to the syntheses of Leu-enkephalin (9) and amyloid-beta (34-42) (10) demonstrates that this strategy comprises an efficient route to new and known "difficult" peptides.

N-Fmoc-α-amino acids were smoothly converted into stable, crystalline N-(Fmoc-α-aminoacyl)benzotriazoles 2a-r (69-90%). Compounds 2b,g reacted with the chiral derivatizing reagent, (+/-)α-methylbenzylamine (5 or 6), to afford α-(N-Fmoc-amino)acid amides 3a,b and 4a,b (average yield 72 %) with no detectable racemization.

Novel N-(Cbz-aminoacyl)thiosemicarbazides 3a-c were cyclized by treatment with sulfuric acid to give 1,3,4-thiadiazoles 4a-c. Compounds 4a-c reacted with N-(Cbz-aminoacyl)- and -dipeptidoylbenzotriazoles to afford chirally pure 1,3,4-thiadiazol-2-yl-substituted amino acids 6a-c and dipeptides 7a-c.

A novel microwave-assisted solid-phase peptide synthesis utilizing N-Fmoc-protected(alpha-aminoacyl)benzotriazoles was applied in the preparation of tri-, tetra-, penta-, hexa-, and heptapeptides in 71% average crude yield.

Esters, sulfones, and ketones were C-aminoimidoylated and C-thiocarbamoylated by benzotriazole-1-carboxamidines 8a-g and 1-(alkyl-or-arylthiocarbamoyl)benzotriazoles 9a-i, respectively. The present work represents the first systematic approach to these compound classes, the few previously known examples of which were obtained by diverse approaches.

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