Enzymatic resolution of racemic secondary cyclic allylic alcohols

New Hydroxylactones and Chloro-Hydroxylactones Obtained by Biotransformation of Bicyclic Halolactones and Their Antibacterial Activity

The aim of this study was to obtain new halolactones with a gem-dimethyl group in the cyclohexane ring (at the C-3 or C-5 carbon) and a methyl group in the lactone ring and then subject them to biotransformations using filamentous fungi. Halolactones in the form of mixtures of two diasteroisomers were subjected to screening biotransformations, which showed that only compounds with a gem-dimethyl group located at the C-5 carbon were transformed. Strains from the genus Fusarium carried out hydrolytic dehalogenation, while strains from the genus Absidia carried out hydroxylation of the C-7 carbon. Both substrates and biotransformation products were then tested for antimicrobial activity against multidrug-resistant strains of both bacteria and yeast-like fungi. The highest antifungal activity against C. dubliniensis and C. albicans strains was obtained for compound 5b, while antimicrobial activity against S. aureus MRSA was obtained for compound 4a.

Oxidation of α,β-Unsaturated Ketones by Organophotocatalysis Using Rhodamine 6G under Visible Light Irradiation: Insight into the Reaction Mechanism

The oxidative transformation of α,β-unsaturated ketones was investigated under visible-light-induced photocatalytic conditions using rhodamine 6G as an organophotocatalyst. In this organocatalysis, the mild co-oxidant bromotrichloromethane (BrCCl3) acts not only as a quencher toward the activated photocatalyst species, having reductant properties, but also as a brominating reagent for the intermediate radicals. This study shows that bromine atom transfer from BrCCl3 to intermediate radicals is a key step in the reaction mechanism of our oxidation method.

Synthesis, structural assignments and antiinfective activities of 3-O-benzyl-carvotacetone and 3-hydroxy-2-isopropyl-5-methyl-p-benzoquinone

In an attempt to synthesize carvotacetone analogues, new 3-O-benzyl-carvotacetone (10) and previously reported 3-hydroxy-2-isopropyl-5-methyl-p-benzoquinone (11) were synthesized from piperitone (7). In this work, we describe the synthesis of 10 and other analogues from 7. Luche reduction of 7 to cis-piperitol (8), followed by benzylation yielded 3-O-benzyl-piperitol (9). Riley oxidation of 9 afforded corresponding ketone 10, 11 and 3-benzyloxy-4-isopropylcyclohex-1-enecarbaldehyde (12). Structures of these compounds were determined based on NMR, IR and LC-MS spectral data. Compound 11, exhibited antiplasmodial activities against chloroquine-sensitive (D6) and resistant (W2) strains of Plasmodium falciparum with IC₅₀ values of 0.697 and 0.653 µg/mL, respectively. In addition, compound 11 was active against Cryptococcus neoformans with an IC₅₀ value of 3.11 µg/mL, compared to reference standard fluconazole (IC₅₀ value of 1.87 µg/mL), while 10 and 12 were inactive against both organisms. This is the first report of the antiplasmodial and anticryptococcal activity of compound 11.

The selectivity of 6-nor-ABA and 7'-nor-ABA for abscisic acid receptor subtypes

Abscisic acid (ABA), a plant hormone, is involved in many plant development processes and environmental stress responses that are regulated by a Pyrabactin Resistant 1 (PYR)/Pyrabactin Resistant-Like (PYL)/Regulatory Component of ABA Receptor (RCAR) receptor protein-mediated signal transduction pathway. In Arabidopsis thaliana, PYL proteins constitute a 14-member family comprising two distinct subclasses: dimeric receptors (PYR1 and PYL1-PYL3) and monomeric receptors (PYL4-PYL13). The individual contributions of PYL subclasses/subtypes with specific physiological actions are still poorly understood; consequently, the development of PYL subclass/subtype-selective agonists should be useful to reveal the different functions of these receptors. In this study, we focused on the ABA analogs 6-nor-ABA and 7'-nor-ABA, which were expected to function as monomeric receptor-selective agonists on the basis of crystal structures of PYL-ABA complexes and sequence alignments of PYL subtypes. In a protein phosphatase 2C (PP2C) assay, the agonist activities of both analogs were lower than those of ABA toward all tested PYL proteins, regardless of subclass/subtype. Nevertheless, we found that 6-nor-ABA acts as a selective agonist at the physiological level: it induced stomatal closure but did not inhibit seed germination and root growth. On the basis of observed inhibitory activity against PP2C among different PYL subtypes, this biological effect of 6-nor-ABA may be attributed to the activity of that agonist on PYL5 and/or PYL6.

Synthesis and Antifeedant Activity of Racemic and Optically Active Hydroxy Lactones with the p-Menthane System

Two racemic and two enantiomeric pairs of new δ-hydroxy-γ-lactones based on the p-menthane system were prepared from racemic and optically active cis- and trans-piperitols. The Johnson-Claisen rearrangement of the piperitols, epoxidation of the γδ-unsaturated esters, and acidic lactonization of the epoxy esters were described. The structures of the compounds were confirmed spectroscopically. The antifeedant activities of the hydroxy lactones and racemic piperitone were evaluated against three insect pests: lesser mealworm, Alphitobius diaperinus (Panzer); Colorado potato beetle, Leptinotarsa decemlineata (Say); and peach-potato aphid, Myzus persicae (Sulz.). The chemical transformation of piperitone by the introduction of a lactone moiety and a hydroxy group changed its antifeedant properties. Behavioral bioassays showed that the feeding deterrent activity depended on the insect species and the structure of the compounds. All hydroxy lactones deterred the settling of M. persicae. Among chewing insects, the highest sensitivity showed A. diaperinus adults.

Structure-related antifeedant activity of halolactones with a p-menthane system against the lesser mealworm, Alphitobius diaperinus Panzer

BACKGROUND

Feeding deterrent activity of synthetic halogen lactones against larvae and adults of the lesser mealworm, Alphitobius diaperinus Panzer, in laboratory choice and no-choice tests was studied. The compounds were synthesised from racemic and enantiomerically enriched (ee = 91-98%) cis- and trans-piperitols, which were obtained from (±)-piperitone.

RESULTS

Structure-activity relationship studies identified several synthetic halolactones with a very strong feeding deterrent activity. The most active were the enantiomeric chlorolactones with chiral centre configurations (1S,4S,5R,6R) and (1R,4R,5S,6S) and their racemic mixture. The racemic bromo- and iodolactones obtained from cis-piperitol and saturated lactones with a chiral centre configuration (1R,4S,6R) were also very good antifeedants in comparison with piperitone. Most of the studied compounds were better antifeedants against adults than against larvae-among the 21 compounds, only one bromolactone with a chiral centre configuration (1S,4R,5R,6R) was a weaker deterrent for adults.

CONCLUSION

Chemical transformation of the piperitone molecule by the introduction of a lactone function and a halogen atom strongly changed its antifeedant properties against the lesser mealworm. Optimum activity is dependent on the presence of a chlorine atom at C-5 of the cyclohexane ring. The activity of bromo- and iodolactones depended strongly on the chiral centre configuration and the halogen substituent.

A Model Study toward the Concise Synthesis of Bromotyrosine Derived Spiroisoxazoline Natural Products and Analogous Core Structures

A model study of the first non-aromatic ring based approach toward α-hydroxyspiroisoxazolines resembling the bromotyrosine derived natural product and analogous spiroisoxazoline core structures were implemented. The desired molecular architecture was achieved through the multifunctionalization of a key 1,3-diketo spiroisoxazoline. Our strategy could serve as an efficient alternative of previously developed approaches that utilize an aromatic ring oxidation as the essential step to synthesize this class of natural products.

Piperitone-derived saturated lactones: synthesis and aphid behavior-modifying activity

Two racemic and two enantiomeric pairs of new saturated lactones with the p-menthane system were obtained. The lactones were synthesized from racemic and enantiomerically enriched cis- and trans-piperitols, which were obtained from piperitone. The structures of the compounds were confirmed by spectroscopic data. The antifeedant activity of piperitone to Myzus persicae was studied, and the biological consequences of structural modifications of piperitone, that is, lactonization and chiral center configuration, were examined as well. The behavioral responses of M. persicae to piperitone and piperitone-derived saturated lactones were investigated to reveal the biological background of their deterrent activity. Piperitone appeared rather neutral or weakly deterrent to aphids. The introduction of a lactone moiety into a piperitone molecule dramatically changed its biological activity. All piperitone-derived lactones evoked negative aphid responses. However, the deterrent activity of individual compounds varied in potency, the time of expression, and the duration of the effect, depending on the spatial structure of the lactone. Lactones (1R,3S,6R)-3-isopropyl-6-methyl-9-oxabicyclo[4.3.0]nonan-8-one and trans-3-isopropyl-6-methyl-9-oxabicyclo[4.3.0]nonan-8-one showed the broadest ranges and the highest potencies and durabilities of deterrent activity to M. persicae: they acted immediately after application, caused a cessation of probing before aphids reached phloem elements, and decreased the quality of phloem sap.