A Non-Fluorinated Monobenzocyclooctyne for Rapid Copper-Free Click Reactions

Photochemical generation of oxa-dibenzocyclooctyne (ODIBO) for metal-free click ligations

Oxa-dibenzocyclooctynes (ODIBO, 2a-c) are prepared by photochemical decarbonylation of corresponding cyclopropenones (photo-ODIBO, 1a-c). While photo-ODIBO does not react with azides, ODIBO is one of the most reactive cyclooctynes exhibiting rates of cycloaddition over 45 M(-1) s(-1) in aqueous solutions. ODIBO is stable under ambient conditions and has low reactivity towards thiols. Photo-ODIBO survives heating up to 160 °C and does not react with thiols.

F-18 labeling protocol of peptides based on chemically orthogonal strain-promoted cycloaddition under physiologically friendly reaction conditions

We introduce the high-throughput synthesis of various (18)F-labeled peptide tracers by a straightforward (18)F-labeling protocol based on a chemo-orthogonal strain-promoted alkyne azide cycloaddition (SPAAC) using aza-dibenzocyclootyne-substituted peptides as precursors with (18)F-azide synthon to develop peptide based positron emission tomography (PET) molecular imaging probes. The SPAAC reaction and subsequent chemo-orthogonal purification reaction with azide resin proceeded quickly and selectively under physiologically friendly reaction conditions (i.e., toxic chemical reagents-free, aqueous medium, room temperature, and pH ≈7), and provided four (18)F-labeled tumor targetable bioactive peptides such as cyclic Arg-Gly-Asp (cRGD) peptide, bombesin (BBN), c-Met binding peptide (cMBP), and apoptosis targeting peptide (ApoPep) in high radiochemical yields as direct injectable solutions without any HPLC purification and/or formulation processes. In vitro binding assay and in vivo PET molecular imaging study using the (18)F-labeled cRGD peptide also demonstrated a successful application of our (18)F-labeling protocol.