Synthetic approaches to a fluorine derivative of carazolol

The objective of this study was to develop a synthesis of a fluorine containing derivative of the beta-adrenergic blocking agent, carazolol. The method could then be employed to synthesize the isotopically labelled analog of the derivative containing the positron emitting 18F for use in quantification of beta-adrenergic receptors in cardiac tissue. The synthetic approach involved introduction into the unsubstituted ring of 4-carbazolol of a small aliphatic side chain for incorporation of a fluorine atom. The tosylate derivative was used both to protect the phenol and to direct substitution into the non-oxygenated ring. It was found that substitutions occurred only at the nitrogen atom of the carbazole nucleus. When this position was blocked by acetylation, no substitution products were found. A third variant of this approach is suggested for further work.