Analogs of phalloidin. D-Abu2-Lys7-phalloin, an F-actin binding analog, its rhodamine conjugate (RLP) a novel fluorescent F-actin-probe, and D-Ala2-Leu7-phalloin, an inert peptide.

The analogs [D-Abu2-Lys7]-phalloin (1) and [D-Ala2-Leu7]-phalloin (2) are obtained by cyclization of the monocyclic thioether peptides 5 and 7 with DCCI and diphenylphosphoro-azidate respectively. For the synthesis of 5 and 7 an intramolecular Savige-Fontana reaction of the linear heptapeptide tert.-butylesters 4 and 6 is applied. On treatment in dilute solution with TFA the classically synthesized peptides 4 and 6 lose their N-terminal Boc groups thus giving rise to the reaction of the Hpi residues with the released cysteine SH-groups. The lysine analog 1 binds to F-actin with an association constant of 1.3 X 10(-6) M whereas analog 2 exhibits practically no affinity. By reaction of 1 with tetramethyl-rhodaminyl-isothiocyanate a fluorescent derivative, rhodaminyl-lysine-phallotoxin (RLP), is obtained as a novel fluorescent probe for the visualization of F-actin in cell preparations.