Fluorinated retinoic acids and their analogues. 2. Synthesis and biological activity of aromatic 4-fluoro analogues.

Ethyl (E,Z,E,E)-3,7-dimethyl-4-fluoro-9-(4-methoxy-2,3,6-trimethylphenyl)nonatetraenoate (10a) has been found to cause a marked regression of chemically induced skin papillomas in mice. A new synthesis of this compound was achieved by condensation of 4-fluoro aldehyde 7 or 8 with the aromatic phosphonium salt 9a. Several analogues (101-e) having different substituted aromatic moieties were also prepared and tested for their antipapilloma effect. The monochloro analogue 10b was shown to have comparable activity to the parent compound 10a.