Asymmetric Total Synthesis of 6-Tuliposide B and Its Biological Activities against Tulip Pathogenic Fungi

The structure-activity relationship was investigated to evaluate the antifungal activities of tuliposides and tulipalins against tulip pathogenic fungi. 6-Tuliposide B was effectively synthesized <I>via</I> the asymmetric Baylis-Hillman reaction. Tuliposides and tulipalins showed antifungal activities against most of the strains tested at high concentrations (2.5 mM), while <I>Botrytis tulipae</I> was resistant to tuliposides. Tulipalin formation was involved in the antifungal activity, tulipalin A showed higher inhibitory activity than 6-tuliposide B and tulipalin B. Both the tuliposides and tulipalins showed pigment-inducing activity against <I>Gibberella zeae</I> and inhibitory activity against <I>Fusarium oxysporum</I> f. sp <I>tulipae</I>. These activities were induced at a much lower concentration (0.05 mM) than the antifungal MIC values.