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The COVID-19 pandemic has strongly impacted our society, producing drastic changes in people's routines and daily mobility, and putting public spaces under a new light. This paper starts with the premise that the use of urban forests and green spaces - where and for who they were available and accessible - increased, when social restrictions were most stringent. It takes an explorative approach to examine changes in attitude towards urban forests and urban green spaces in terms of attraction (i.e., as the actual use behaviour), intended use (i.e., intention of going to green spaces), and civic engagement in relation to green spaces. In particular, it analyses the responses to a survey of 1987 respondents in Belgium and statistically examines the relationship between sociodemographic characteristics, urbanisation characteristics, actual and intended green space use, and changes in attitudes towards green spaces and civic engagement. The findings show that highly educated citizens experienced an increase in actual and intended use of green spaces during the pandemic, but that this increase differs among sociodemographic profiles such as impact of age or access to private green, and depends on their local built environment characteristics. In addition, the COVID-19 pandemic has strongly impacted citizens' attitudes, as well as (intended) behaviour and civil engagement with respect to the green spaces in their area., Competing Interests: The authors report no declarations of interest., (© 2021 Elsevier GmbH. All rights reserved.)

Our study investigates the biochemical and functional impact of selective histone deacetylase 6 (HDAC6) inhibitors, a promising class of novel therapeutics, in several cancer models. Selective HDAC6 inhibitors (Tubathian A, Tubastatin A, Tubacin and Ricolinostat) and a non-selective HDAC inhibitor (Vorinostat) were evaluated on cancer cell lines derived from multiple tumour types in both an in vitro and in vivo setting as potential cancer therapeutics. Selective HDAC6 inhibitors resulted in α-tubulin acetylation with no impact on histone acetylation but failed to show any anti-cancer properties. Only the use of high concentrations of selective HDAC6 inhibitors resulted in co-inhibition of other HDAC enzymes and consequently in reduced growth, migratory and/or invasive activity of cancer cells in vitro as well as in vivo. The specificity of HDAC6 inhibition was confirmed using a CRISPR/Cas9 knockout cell line. Our results suggest that selective HDAC6 inhibitors may fall short as potential single agent anti-cancer drugs and prove that many previous data regarding this promising class of compounds need to be interpreted with great care due to their use in high concentrations resulting in low selectivity and potential off-target effects., (© 2019 UICC.)

Recent studies point towards the possible disadvantages of using hydroxamic acid-based zinc-binding groups in HDAC inhibitors due to e.g. mutagenicity issues. In this work, we elaborated on our previously developed Tubathian series, a class of highly selective thiaheterocyclic HDAC6 inhibitors, by replacing the benzohydroxamic acid function by an alternative zinc chelator, i.e. , an aromatic trifluoromethyl ketone. Unfortunately, these compounds showed a reduced potency to inhibit HDAC6 as compared to their hydroxamic acid counterparts. In agreement, the most active trifluoromethyl ketone was unable to influence the growth of SK-OV-3 ovarian cancer cells nor to alter the acetylation status of tubulin and histone H3. These data suggest that replacement of the zinc-binding hydroxamic acid function with a trifluoromethyl ketone zinc-binding moiety within reported benzohydroxamic HDAC6 inhibitors should not be considered as a standard strategy in HDAC inhibitor development.

This paper provides an overview of the synthesis and biological activity of the most representative benzohydroxamic acid-based histone deacetylase inhibitors published to date. Benzohydroxamic acids comprise an important class of HDAC inhibitors, and recently several of these structures have been evaluated in clinical trials for the treatment of a variety of cancers. In this overview, benzohydroxamic acids were divided in four different classes based on their reported selectivity towards zinc-dependent HDACs: a first and major class consists of HDAC6 selective inhibitors, a second class deals with pan-HDAC inhibitors, a third class comprises HDAC8 selective inhibitors and a fourth, minor class includes dual HDAC6/8 selective inhibitors. Through this approach, structure-activity relationships were identified for each class, which could help future researchers in the design and development of novel benzohydroxamic acid-based HDAC inhibitors., (Copyright © 2017 Elsevier Masson SAS. All rights reserved.)

Selective inhibitors of histone deacetylase 6 (HDAC6) are an emerging class of pharmaceuticals due to the involvement of HDAC6 in different pathways related to neurodegenerative diseases, cancer, and immunology. Herein, the synthesis of ten new benzohydroxamic acids, constructed by employing the tetrahydrobenzothiazepine core as a privileged pharmacophoric unit, is described. This is the first report on the synthesis and isolation of octahydrodibenzothiazepines and octahydro-6H-benzocycloheptathiazepines, which were then used to develop a new class of HDAC6 inhibitors. Evaluations of their HDAC-inhibiting activity resulted in the identification of cis-N-(4-hydroxycarbamoylbenzyl)-1,2,3,4,4a,5,11,11a-octahydrodibenzo[b,e][1,4]thiazepine-10,10-dioxide and cis-N-(4-hydroxycarbamoylbenzyl)-7-trifluoromethyl-1,2,3,4,4a,5,11,11a-octahydrodibenzo[b,e][1,4]thiazepine-10,10-dioxide as highly potent and selective HDAC6 inhibitors with activity in the low nanomolar range, which also show excellent selectivity on the enzymatic and cellular levels. Furthermore, four promising inhibitors were subjected to an Ames fluctuation assay, which revealed no mutagenic effects associated with these structures., (© 2017 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.)

Curcumin, a natural compound extracted from the rhizomes of Curcuma Longa, is known to display pronounced anticancer activity but lacks good pharmacokinetic properties. In that respect, augmenting the water solubility by structural modification of the curcumin scaffold may result in improved bioavailability and pharmacokinetics. A possible scaffold modification, especially important for this study, concerns the imination of the labile β-diketone moiety in curcumin. Previous work revealed that novel N-alkyl β-enaminones showed a similar water solubility as compared to curcumin, accompanied by a stronger anti-proliferative activity. To extend this β-enaminone compound library, new analogues were prepared in this work using more polar amines (hydroxyalkylamines and methoxyalkylamines instead of alkylamines) with the main purpose to improve the water solubility without compromising the biological activity of the resulting curcuminoids. Compared to their respective parent compounds, i.e. curcumin and bisdemethoxycurcumin, the bisdemethoxycurcumin N-(hydroxy/methoxy)alkyl enaminone analogues showed better water solubility, antioxidant and anti-proliferative activities. In addition, the curcumin enaminones displayed activities comparable to or better than curcumin, and the water solubility was improved significantly. The constructed new analogues may thus be of interest for further exploration concerning their impact on oxidative stress related diseases such as cancer., (Copyright © 2016 Elsevier Ltd. All rights reserved.)

Curcuminoids are high-potential drugs targeting multiple components of vital signaling pathways without being toxic, and are therefore considered to be valuable lead structures in medicinal chemistry. Unfortunately, most curcuminoids poorly reach their site of action because of low bioavailability issues, (partly) associated with the labile β-diketo structure. In that respect, curcumin derivatives bearing a central β-enaminone fragment may have improved solubility and intestinal stability, and therefore may represent a new class of analogs with higher bioactivity. In that mindset, thirteen N-alkyl enaminones were efficiently synthesized via a novel approach, using montmorillonite K10 clay and microwave irradiation. These compounds were then characterized in terms of solubility and chemical anti-oxidant properties, and were applied in screening assays for cell toxicity, growth and oxidative stress using CHO-K1, EA.hy926, HT-29 and Caco-2 cell lines. Compared to native curcumin, many nitrogen derivatives showed a stronger antiproliferative effect, which was highly structure and cell type dependent. In addition, the correlation between cell viability and reactive oxygen species production was limited. Therefore, this set of novel curcumin derivatives may be useful to unravel other mechanisms of oxidative stress-related diseases, and eventually be used as more bioavailable and bioactive alternatives for native curcumin., (Copyright © 2016 Elsevier Masson SAS. All rights reserved.)

Despite the growing importance of prebiotics in nutrition and gastroenterology, their structural variety is currently still very limited. The lack of straightforward procedures to gain new products in sufficient amounts often hampers application testing and further development. Although the enzyme sucrose phosphorylase can be used to produce the rare disaccharide kojibiose (α-1,2-glucobiose) from the bulk sugars sucrose and glucose, the target compound is only a side product that is difficult to isolate. Accordingly, for this biocatalyst to become economically attractive, the formation of other glucobioses should be avoided and therefore we applied semi-rational mutagenesis and low-throughput screening, which resulted in a double mutant (L341I_Q345S) with a selectivity of 95% for kojibiose. That way, an efficient and scalable production process with a yield of 74% could be established, and with a simple yeast treatment and crystallization step over a hundred grams of highly pure kojibiose (>99.5%) was obtained.

The synthesis of novel isoform-selective HDAC inhibitors is considered to be an important, emerging field in medicinal chemistry. In this paper, the preparation and assessment of thirteen selective HDAC6 inhibitors is disclosed, elaborating on a previously developed thiaheterocyclic Tubathian series. All compounds were evaluated in vitro for their ability to inhibit HDAC6, and a selection of five potent compounds was further screened toward all HDAC isoforms (HDAC1-11). The capability of these Tubathian analogs to inhibit α-tubulin deacetylation was assessed as well, and ADME/Tox data were collected. This thorough SAR evaluation revealed that the oxidized, para-substituted hydroxamic acids can be recognized as valuable lead structures in the pursuit of novel potent and selective HDAC6 inhibitors.

A small library of 3-[(4-hydroxycarbamoylphenyl)aminomethyl]benzothiophenes was prepared and assessed as a novel class of HDAC6 inhibitors, leading to the identification of three representatives as potent and selective HDAC6 inhibitors. Further tests with regard to inflammatory responses indicated that HDAC6 inhibition can be uncoupled from transcriptional inhibition at the level of activated NF-κB, AP-1, and GR.

A two-step process is reported for the anomeric phosphorylation of galactose, using trehalose phosphorylase as biocatalyst. The monosaccharide enters this process as acceptor but can subsequently be released from the donor side, thanks to the non-reducing nature of the disaccharide intermediate. A key development was the creation of an optimized enzyme variant that displays a strict specificity (99%) for β-galactose 1-phosphate as product.

Eight N-(4-hydroxycarbamoylbenzyl)-1,2,4,9-tetrahydro-3-thia-9-azafluorenes were efficiently prepared as sulfur analogues of Tubastatin A and thus evaluated as new HDAC6 inhibitors. All compounds exhibited potency against HDAC6, and four of them were active in the nanomolar range (IC(50) = 1.9-22 nM). Further analysis revealed that the sulfone derivatives (designated as Tubathians) are superior to their non-oxidized sulfide analogues, and the two most active sulfones showed good to excellent HDAC6 selectivity compared to all other HDAC isoform classes.

Purine-β-lactam chimera were prepared as a novel class of hybrid systems through N-alkylation of 6-benzylamino- or 6-benzyloxypurine with (ω-haloalkyl)-β-lactams, followed by reductive ring opening of the β-lactam ring by LiEt(3)BH to provide an entry into the class of purine-aminopropanol hybrids. Both new types of hybrid systems were assessed for their antiviral activity and cytotoxicity, resulting in the identification of eight purine-β-lactam hybrids and two purine-aminopropanol hybrids as promising lead structures.

The interplay between metals and N-heterocyclic carbenes (NHCs) has provided a window of opportunities for the development of novel catalytic strategies within the past few years. The recent successful combination of Brønsted acids with NHCs has added a new dimension to the field of cooperative catalysis, enabling the stereoselective synthesis of functionalized pyrrolidin-2-ones as valuable scaffolds in heterocyclic chemistry. This Commentary will briefly highlight the concept of N-heterocyclic carbene/Brønsted acid cooperative catalysis as a new and powerful methodology in organic chemistry.