Chemoselective fluorination and chemoinformatic analysis of griseofulvin: Natural vs fluorinated fungal metabolites

Abstract

Griseofulvin is a fungal metabolite and antifungal drug used for the treatment of dermatophytosis in both humans and animals. Recently, griseofulvin and its analogues have attracted renewed attention due to reports of their potential anticancer effects. In this study griseofulvin (1) and related analogues (2–6, with 4 being new to literature) were isolated from Xylaria cubensis. Six fluorinated analogues (7–12) were synthesized, each in a single step using the isolated natural products and Selectflour, so as to examine the effects of fluorine incorporation on the bioactivities of this structural class. The isolated and synthesized compounds were screened for activity against a panel of cancer cell lines (MDA-MB-435, MDA-MB-231, OVCAR3, and Huh7.5.1) and for antifungal activity against Microsporum gypseum. A comparison of the chemical space occupied by the natural and fluorinated analogues was carried out by using principal component analysis, documenting that the isolated and fluorinated analogues occupy complementary regions of chemical space. However, the most active compounds, including two fluorinated derivatives, were centered around the chemical space that was occupied by the parent compound, griseofulvin, suggesting that modifications must preserve certain attributes of griseofulvin to conserve its activity.

The value of universally available raw NMR data for transparency, reproducibility, and integrity in natural product research

“…Finally, the coupling constants ( J CF ) for 13 C– 19 F are quite large (up to 250 Hz), providing information about the location of the F atom and the connectivity of adjacent atoms 278,285. In fact, these large J CF couplings are very helpful in structure elucidation, akin to using HSQC data to assign how a 13 C signal can be correlated with its attached 1 H signals 280,286. Additionally, relatively simple experiments, such as a 1 H decoupled 13 C experiment, will display splitting due to the 13 C– 19 F coupling, and upon first inspection, such data may be quite foreign, especially to a student.…”

Mapping the Fungal Battlefield: Using in situ Chemistry and Deletion Mutants to Monitor Interspecific Chemical Interactions Between Fungi

“…To obtain baseline data, the monoculture of X. cubensis was sampled by droplet probe, and the LC-MS base peak chromatogram only showed two peaks, which corresponded to griseofulvin ( 8 ) and dechlorogriseofulvin ( 9 ) as determined by comparison of accurate mass and RT of a standard (El-Elimat et al, 2013; Paguigan et al, 2017). Griseofulvin ( 8 ) and dechlorogriseofulvin ( 9 ) were present in multiple spots across the mycelium, with both more concentrated at the mycelial edge.…”

“…The fungal growth was extracted and purified to isolate compounds that were characterized. In the co-culture griseofulvin ( 8 ) and dechlorogriseofulvin ( 9 ) (Paguigan et al, 2017), which were present in the monoculture, were isolated, as were the two analogs 5′-hydroxygriseofulvin ( 10 ) and dechloro-5′-hydroxygriseofulvin ( 11 ) (Paguigan et al, 2017), which were not observed in monoculture (Supplementary Figures S12–S15). The mycotoxins cytochalasin D ( 12 ) (Jikai et al, 2002), cytochalasin Q ( 13 ) (El-Elimat et al, 2013), cytochalasin C ( 14 ), zygosporin E ( 15 ) (Vedejs et al, 1988; Edwards et al, 1989), and 7- O -acetylcytochalasin B ( 16 ) (Capasso et al, 1991), (Figure 7) were observed in monoculture, albeit at extremely low concentrations that did not afford structural characterization.…”

“…In situ visualization of griseofulvin production in monoculture versus co-culture was different, due to the differential accumulation of griseofulvin ( 8 ), suggesting how antagonistic or combative species use allelochemicals for attack on other microbes to break through the conflict zone. Griseofulvin is an antifungal compound that can be classified as an allelochemical (allomone), which is implicated in interspecies interactions that can benefit the producing organism, but not the receiving one (Drijfhout, 2001; Sica et al, 2016c; Paguigan et al, 2017). The question of how fungi protect themselves from such armaments is often pondered.…”

“…In this study, we evaluated the co-culturing of two fungi, Aspergillus fischeri and Xylaria cubensis, in situ and observed distinct chemical profile changes resulting from the interspecific interactions between them. X. cubensis commonly occurs as an endophyte (endosymbiotic) and decomposer (saprobic) (Helaly et al, 2018) and biosynthesizes the fungistatic secondary metabolite griseofulvin, an FDA-approved drug (Sica et al, 2016c; Paguigan et al, 2017). Fungistatic denotes that it inhibits fungal growth, rather than kills competing fungi, and we hypothesized, therefore, that the resulting stress in a co-culture environment would allow us to examine how secondary metabolite production changes when the two species interact.…”