RESUMEN
Lichens are symbiotic organisms comprised of mycobionts and photobiont partners. They are known to produce bioactive secondary metabolites and most of these are biosynthesized by mycobionts. Investigations of cultures of isolated lichen-associated fungi have shown promise for the discovery of cytotoxic compounds. Thus, the lichen-associated fungus Penicillium aurantiacobrunneum was studied for its potential to produce novel compounds and the new sterols (20S*)-hydroxy-24(28)-dehydrocampesterol (1), 7α-methoxy-8ß-hydroxypaxisterol (2), 14-nor-epicoccarine A (3) and 14-nor-epicoccarine B (4), as well as the known compound PF1140 (5), were isolated. The structures of these compounds were elucidated using methods including nuclear magnetic resonance (NMR) spectroscopy and high-resolution electrospray ionization mass spectrometry (HRESIMS). Following cytotoxicity assays, compound 1 demonstrated activity against the pancreatic adenocarcinoma epithelial HPAC cell line at 17.76 ± 5.35 µM. Since the structures of compounds 3 and 4 were very similar to tetramic acid derivatives that were reported to be biosynthesized from a polyketide synthase- non-ribosomal peptide synthetase (PKS-NRPS) hybrid pathway, a plausible biosynthetic route for production in P. aurantiacobrunneum is proposed herein.
RESUMEN
CYP5122A1, an enzyme involved in sterol biosynthesis in Leishmania, was recently characterized as a sterol C4-methyl oxidase. Screening of a library of compounds against CYP5122A1 and CYP51 from Leishmania resulted in the identification of two structurally related classes of inhibitors of these enzymes. Analogs of screening hit N-(3,5-dimethylphenyl)-4-(pyridin-4-ylmethyl)piperazine-1-carboxamide (4a) were generally strong inhibitors of CYP51 but were less potent against CYP5122A1 and typically displayed weak inhibition of L. donovani promastigote growth. Analogs of screening hit N-(4-(benzyloxy)phenyl)-4-(2-(pyridin-4-yl)ethyl)piperazine-1-carboxamide (18a) were stronger inhibitors of both CYP5122A1 and L. donovani promastigote proliferation but also remained selective for inhibition of CYP51. Two compounds in this series, N-(4-((3,5-bis(trifluoromethyl)benzyl)oxy)phenyl)-4-(2-(pyridin-4-yl)ethyl)piperazine-1-carboxamide (18e) and N-(4-((3,5-di-tert-butylbenzyl)oxy)phenyl)-4-(2-(pyridin-4-yl)ethyl)piperazine-1-carboxamide (18i) showed modest selectivity for inhibiting L. donovani promastigote proliferation compared to J774 macrophages and were effective against intracellular L. donovani with EC50 values in the low micromolar range. Replacement of the 4-pyridyl ring present in 18e with imidazole resulted in a compound (4-(2-(1H-imidazol-1-yl)ethyl)-N-(4-((3,5-bis(trifluoromethyl)benzyl)oxy)phenyl)piperazine-1-carboxamide, 18p) with approximately fourfold selectivity for CYP5122A1 over CYP51 that inhibited both enzymes with IC50 values ≤ 1 µM, although selective potency against L. donovani promastigotes was lost. Compound 18p also inhibited the proliferation of L. major promastigotes and caused the accumulation of 4-methylated sterols in L. major membranes, indicating that this compound blocks sterol demethylation at the 4-position in Leishmania parasites. The molecules described here may therefore be useful for the future identification of dual inhibitors of CYP51 and CYP5122A1 as potential antileishmanial drug candidates and as probes to shed further light on sterol biosynthesis in Leishmania and related parasites.
RESUMEN
Fluorescent nucleoside analogs, commonly used to explore nucleic acid dynamics, recognition and damage, frequently respond to a single environmental parameter. Herein we address the development of chromophores that can simultaneously probe more than one environmental factor while having each associated with a unique spectroscopic signature. We demonstrate that an isomorphic emissive pyridine-modified 2-deoxy-uridine 1, containing multiple sensory elements, responds to changes in acidity, viscosity, and polarity. Protonation of the pyridine moiety (pK(a) 4.4) leads to enhanced emission (λ(em) =388 nm) and red-shifted absorption spectra (λ(abs) =319 nm), suggesting the formation of an intramolecular hydrogen bond with the neighboring pyrimidine carbonyl. This "locked" conformation can also be mimicked by increasing solvent viscosity, resulting in a stark enhancement of emission quantum yield. Finally, increasing solvent polarity substantially impacts the chromophore's Stokes shift [from 5.8×10(3) cm(-1) at E(T) (30)=36.4 kcal mol(-1) to 9.3 ×10(3) cm(-1) at E(T) (30)=63.1 kcal mol(-1)]. The opposite effect is seen for the impact of solvent polarity of the protonated form. The characteristic photophysical signature induced by each parameter facilitates the exploration of these environmental factors both individually and simultaneously.