The symmetrical disulfide psammaplin A from the marine sponge Pseudoceratina sp. was synthesized and structurally altered by replacement of one of the α-(hydroxyimino)acyl units by a fluorescent 4-coumarinacetyl moiety. Thus, the first fluorescent analogs of psammaplin A were obtained. Structural variation also covered the substitution pattern of the phenyl ring. Cytotoxicity of psammaplin A against the mouse fibroblast cell line L-929 (IC(50) 0.42 μg mL(-1)) was about two-fold higher than that of the fluorescent hybrid compounds, whereas the disulfide containing two 4-coumarinacetyl moieties was inactive. Fluorescence microscopy revealed uptake of the 4-coumarinacetyl-α-(hydroxyimino)acyl hybrids into the cytoplasm leading to fluorescence in close proximity of the nuclear envelope, most likely in the Golgi apparatus. We did not observe strong fluorescence inside the nucleus, where most of the target histone deacetylases are located. We conclude that reduction of the disulfide probably takes place outside the nucleus. The psammaplin-derived thiol exhibited potent activity against histone deacetylase in the low nanomolar range, but diminished cytotoxicity. Antimicrobial activity of the new derivatives was also determined.

With raising prevalence of obesity, the regulation of human body fat is increasingly relevant. The modulation of fatty acid uptake by enterocytes represents a promising target for body weight maintenance. Recent results demonstrated that the trigeminal active compounds capsaicin, nonivamide, and trans-pellitorine dose-dependently reduce fatty acid uptake in differentiated Caco-2 cells as a model for the intestinal barrier. However, non-pungent alternatives have not been investigated and structural determinants for the modulation of intestinal fatty acid uptake have not been identified so far. Thus, based on the previous results, we synthesized 23 homovanillic acid esters in addition to the naturally occurring capsiate and screened them for their potential to reduce intestinal fatty acid uptake using the fluorescent fatty acid analog Bodipy-C12 in differentiated Caco‑2 cells as an enterocyte model. Whereas pre-incubation with 100 µM capsiate did not change fatty acid uptake by Caco-2 enterocytes, a maximum inhibition of −47% was reached using 100 µM 1‑methylpentyl-2-(4-hydroxy-3-methoxy-phenyl)acetate. Structural analysis of the 24 structural analogues tested in the present study revealed that a branched fatty acid side chain, independent of the chain length, is one of the most important structural motifs associated with inhibition of fatty acid uptake in Caco-2 enterocytes. The results of the present study may serve as an important basis for designing potent dietary inhibitors of fatty acid uptake.

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