On the photochemical reaction of pyridinium salts with nucleophiles.

DFT calculations on the photochemical reaction of 1-n-N-butylpyridinium salt in water with hydroxide anion is in agreement with a singlet state process where the S2 state at λ = 253 nm can be converted into a Dewar isomer (2-butyl-2-azabicyclo[2.2.0]hexa-2,5-dien-2-yl cation). The Dewar isomer can react with hydroxide anion giving the product, 6-n-butyl-6-azabicyclo[3.1.0]hex-3-en-2-ol.

Hydrogen atom transfer in the photochemical isomerization of hydrazones of 1,2,4-oxadiazole derivatives.

DFT calculations on the photoisomerization of hydrazones of 1,2,4-oxadiazole derivatives to 1,2,5-triazoles have been performed showing that the reaction occurred through the first excited singlet state. The Z isomer gave the reaction through a hydrogen atom transfer of the hydrazonic nitrogen atom to the nitrogen atom in four position on the oxadiazole ring. In this case, the isomerization was a concerted reaction. The E isomer could undergo the same reaction. However, it could not be a concerted reaction but required the presence of a ring opening intermediate.

The Paternò-Büchi reaction - a comprehensive review.

The photochemical reaction between an excited state of carbonyl compounds and an alkene to give the oxetane deriving from a cycloaddition reaction (the Paternò-Büchi reaction) is presented. The mechanism of the reaction is discussed on the basis of kinetic, spectroscopic, and theoretical evidence, showing that the reaction can involve both singlet and triplet excited states of the carbonyl compounds, the high probable presence of an exciplex, and the possible presence of electron transfer processes, and when triplet excited carbonyl compounds are involved, the presence of a biradical intermediate is observed. The reactivity of electron-poor and electron-rich alkenes is discussed. Regio- and stereochemical behavior of the reaction are presented showing that, in some cases, very high regio- and stereoselectivities are obtained. The possible theories explaining this behavior are presented. In this field, the stereoselectivity observed, when chiral auxiliaries are used, when the reaction is performed in organized media, and when the presence of a hydroxyl directing effect can be supposed, is presented. The effect of light, temperature, solvent on the reaction is discussed. The possible application of this reaction in organic synthesis is discussed, presenting both previous synthetic schemes where the synthesis of an oxetane is a key step, the possible use of the oxetane in synthesis, and comparing the photochemical approach with the other approaches used to synthesize the oxetane ring.

The chiral photocycloaddition of a cyclohexenone derivative with a chiral alkene. A DFT study.

The photochemical reaction of 3-carboxymethylcyclohexenone with a cyclohexene bearing a chiral auxiliary group has been examined in a DFT study. GIAO simulation of the NMR spectra (DFT/B3LYP/6-311G++(d,2p) level of theory) is not in agreement with the syn-anti-syn product described in the literature for this reaction but is in agreement with the formation of a syn-cis-syn dimer. The analysis of the frontier orbitals involved in this reaction shows that the main interaction is that between the HOMO of the alkene and the LSOMO of the carbonyl compound in its first excited triplet state. The atomic coefficients do not allow a frontier orbital control of the regiochemistry of the reaction. The study of the possible biradical intermediates and the energies of the transition states involved agree with the formation of a syn-cis-syn biradical intermediate. The coupling of the radical carbon atoms in this biradical intermediate allows the obtainment of a more stable dimer. Furthermore, the coupling reaction occurs via a conrotatory process that is able to give only one of the possible syn-cis-syn dimers.

Pollination features and floral volatiles of Gymnospermium scipetarum (Berberidaceae).

The discovery of few isolated populations of Gymnospermium scipetarum (since now considered as an amphi-Adriatic endemic) in the S-Apennines prompted to investigate, also for conservation purposes, some aspects of its reproductive biology. We aim: (1) to determine if insects play an important role in pollination; (2) to describe the pollinator community; (3) to detect floral scent composition. Experiments of insect exclusion were carried out in the field using 24 flowering individuals: one raceme was capped whereas the nearest one was used as control to ascertain differences in seed set. Pollinator community was detected during the blooming phase of two consecutive flowering seasons by visual observation; insect identification was made at the highest possible taxonomic resolution with the help of digital photographs. In order to determine the chemical composition of the volatiles, we used SPME sampling of cultivated plants. Mann-Whitney U test reveals significant differences for treatment in mean seed set with very low values for capped flowers, thus clearly indicating as insects are crucial for successful pollination. During the 42 h of observations we detected 326 visitors belonging to only three guilds: 79% were Diptera, 20% Hymenoptera and 1% Coleoptera. We identified overall 36 floral organic compounds with only two compounds common to the other studied Berberidaceae. Ambrox was never identified before in the floral scents of any angiosperm. The presence in the scent of several aldehydes and one ketone (benzophenone) could be related to the detected dominance of muscoid flies as pollinators. Floral morphology and composition of the pollinators community indicate a generalist pollination behaviour probably related to its phenology and habitat preference. The possibility of being pollinated also by muscoid flies can be considered an advantage for the reproductive fitness of the species, since these Diptera are abundant in the mountain pastures surrounding the forest habitat of Gymnospermium.

A DFT Study of the Photochemical Dimerization of Methyl 3-(2-Furyl)acrylate and Allyl Urocanate.

A DFT study of the photochemical dimerization of methyl 3-(2-furyl)acrylate is reported. The photochemical reaction gave a mixture of two dimers with high regioselectivity and good stereoselectivity. Calculations showed that benzophenone was able to act as a photosensitizer of the reaction. This compound populated the first excited triplet state of the substrate. The frontier orbitals interaction between LSOMO of the triplet state and HOMO of the ground state accounted for the observed high regioselectivity. Furthermore, the energy of all the possible triplet biradicals has been calculated, showing that the precursor of the main product was the triplet biradical with the lowest energy. The coupling of the atomic coefficients on the radical centres in the biradical intermediates allowed to justify the observed products. The same behavior was observed in the case of the photochemical dimerization of an urocanate ester and in the dimerization of liquid methyl cinnamate.

Oxetane synthesis through the Paternò-Büchi reaction.

The Paternò-Büchi reaction is a photochemical reaction between a carbonyl compound and an alkene to give the corresponding oxetane. In this review the mechanism of the reaction is discussed. On this basis the described use in the reaction with electron rich alkenes (enolethers, enol esters, enol silyl ethers, enanines, heterocyclic compounds has been reported. The stereochemical behavior of the reaction is particularly stressed. We pointed out the reported applications of this reaction to the synthesis of naturally occuring compounds.

Volatile organic compounds from Citrus australasica growing in Basilicata (Southern Italy).

SPME-GCMS analysis of vesicles of Sanguinea cultivar showed the presence of limonene (45.63%), sabinene (22.65%), and bicyclogermacrene (10.80%). The analysis of the peel showed that the main components were limonene (48.24%), sabinene (37.15%), and α-pinene (4.26%). In Pink Ice cultivar the main components of the vesicles were sabinene (31.68%), limonene (20.71%), and bicyclogermacrene (14.18%). Peel analysis showed the presence of limonene (37.68%), sabinene (33.33%), and α-pinene (5.55%). In Faustrime limonene (51.54%), γ-terpinene (10.01%), α-bergamotene (7.48%), ß-bisabolene (7.07%), and a-phellandrene (5.68%) were detected. In peel analysis limonene (27.84%), α-pinene (9.41%), γ-terpinene (10.00%), and citronellal (10.51%) were found.

Composition and seasonal variation of volatile organic compounds in Santolina etrusca (Lacaita) Marchi & D'Amato found at Acquapendente (Viterbo, Central Italy).

The main component of the essential oil of Santolina etrusca is viridiflorol (23.98-42.23%). a compound not found in the essential oil of Santolina camaecyparissus. The main component found in this study is the same found in the essential oil obtained from plants collected in Tuscany and Umbria. However, there are important differences in the other components of the essential oil, where we found the presence of eucalyptol (2.98-9.73%) and germacrene D (2.39-19.59%). Finally, seasonal variation of the essential oil composition induces a reduction of sesquiterpenes amounts with the corresponding increase of the monoterpenes during spring and summer.

HS-SPME-GC-MS determination of the scent of Anacamptis taxa (fam. Orchidaceae) from Basilicata (Southern Italy).

The scent of Anacamptis species has been analyzed by using HS-SPME-GC-MS. The sample was collected in Basilicata (Southern Italy). Every species showed a different composition of the scent in the analyses we performed. 1,2,4-Trimethoxybenzene and methyl 4-mehoxybenzoate were the main components of that of Anacamptis coriophora subsp. fragrans. The scent of Anacamptis laxiflora was due to the presence of caryophyllene. Linear hydrocarbons but also decanal were components of the scent of Anacamptis pyramidalis. Eucalyptol was found in the scent of Anacamptis papilonacea. Finally, ß-sesquiphellandrene was the main component of the scent of Anacamptis morio.

A potential host and virus targeting tool against COVID-19: Chemical characterization, antiviral, cytoprotective, antioxidant, respiratory smooth muscle relaxant effects of Paulownia tomentosa Steud.

COronaVIrus Disease 2019 (COVID-19) is a newly emerging infectious disease that spread across the world, caused by the novel coronavirus Severe Acute Respiratory Syndrome CoronaVirus 2 (SARS-CoV-2). Despite the advancements in science that led to the creation of the vaccine, there is still an urgent need for new antiviral drugs effective against SARS-CoV-2. This study aimed to investigate the antiviral effect of Paulownia tomentosa Steud extract against SARS-CoV-2 and to evaluate its antioxidant properties, including respiratory smooth muscle relaxant effects. Our results showed that P. tomentosa extract can inhibit viral replication by directly interacting with both the 3-chymotrypsin-like protease and spike protein. In addition, the phyto complex does not reduce lung epithelial cell viability and exerts a protective action in those cells damaged by tert-butyl hydroperoxide , a toxic agent able to alter cells' functions via increased oxidative stress. These data suggest the potential role of P. tomentosa extract in COVID-19 treatment, since this extract is able to act both as an antiviral and a cytoprotective agent in vitro.

Photochemical isomerization of aryl hydrazones of 1,2,4-oxadiazole derivatives into the corresponding triazoles.

The photochemical version of the Boulton-Katritzky reaction has been studied, examining the behaviour of the arylhydrazones of 3-benzoyl-5-X-1,2,4-oxadiazoles. The effect of several modifications of the substrates structure (the E and/or Z structures of arylhydrazones, the possible presence of substituents in the arylhydrazono moiety, and the nature of substituents at C-5 of the 1,2,4-oxadiazole ring) on the course of the photochemical rearrangement has been examined.

Characterization of the volatile fraction of mastic oil and mastic gum.

GC-MS of ethyl acetate solutions and HS-SPME-GC-MS of mastic oil and mastic gum showed the presence of α-pinene and ß-myrcene as main components of the mixture. In the GC-MS analysis of mastic oil 19 compounds were detected, while mastic gum allowed to detect only twelve compounds. Mastic gum showed the presence of compounds with a higher molecular weight. In HS-SPME analysis the amount of ß-myrcene increased in comparison to the results obtained in the analyses performed in solution. The relative ratio between α-pinene and ß-myrcene showed that SPME analysis induces a preferential detection for ß-myrcene (α-pinene/ß-myrcene in the mastic oil 16.18 in GC-MS analysis, and 5.06 in SPME analysis; α-pinene/ß-myrcene in mastic gum 10.64 in GC-MS analysis, and 2.25 in SPME analysis). These results can be explained considering a different absorption selectivity of these compounds on the SPME fiber.

Fragrance components of Gymnadenia conopsea and Gymnadenia odoratissima collected at several sites in Italy and Germany.

The SPME-GC-MS analysis of the aroma components of Gymnadenia conopsea subsp. conopsea, subsp. densiflora, var. alpina and Gymnadenia odoratissima var. odoratissima, var. idae were reported. The main components of in total 78 found in G. conopsea subsp. conopsea were elemicin, cis-9-hexadecenal, hexadecanal, isoelemicin and (Z)-11-hexadecen-1-ol acetate; in subsp. densiflora benzyl benzoate, eugenol and trans-isoeugenol; in var. alpina benzyl benzoate, methyleugenol and elemicin. In the scent of G. odoratissima var. odoratissima were found 2-phenylethyl acetate, eugenol and pentadecane, in var. idae mainly C15-C21 alkanes and C16, C18 carbonic acids and some isoprenoid-derivatives. As all tested Gymnadenia-taxa are allogamous, the differences in scent composition may play a role in pollinator attraction.

The scent of Neotinea orchids from Basilicata (Southern Italy).

The scent of Neotinea species has been performed by using solid-phase microextraction- gas chromatography- mass spectrometry (SPME-GC-MS). The scent of Neotinea ustulata showed the presence of 9-tricosene, 1-nonadecanol and heinecosane. The analysis of the scent of Neotinea tridentata gave α-ionone as the main component. The scent of Neotinea lactea showed the presence of pentadecane, heptadecane and isopropyl palmitate. Neotinea maculata showed the presence in the scent of 1-decene and ethyl dodecanoate.

The composition of the aroma of Serapias orchids in Basilicata (Southern Italy).

The SPME-GC-MS analysis of the aroma components of Serapias cordigera, Serapias cordigera subsp. lucana, Serapias vomeracea, Serapias lingua, and Serapias parviflora were reported. The relevant components of the scent of Serapias cordigera were α-amorphene, ethyl oleate, heneicosane, heptadecane, 2-heptadecanone, ethyl elaidate, pentadecane, octadecane, farnesylacetaldehyde, nonadecane, and ethyl stearate. Serapias cordigera subsp. lucana gave α-amorphene, pentadecane, propyl undecanoate, heptadecane, ethyl elaidate and oleate, ethyl stearate, and 8-heptadecene. Serapias vomeracea showed pentadecane, 5-nonadecene, 1-nonadecene, 3-heptadecene, benzyl benzoate, 2-undecanone, and octadecane. Serapias lingua showed the presence of heptadecane, 3-heptadecene, isopropyl myristate, pentadecane, nonadecane, isopropyl palmitate, octadecane, and benzyl benzoate. Serapias parviflora gave pentadecane, pentadecene, hexadecane, heptadecane, nonadecane, and ethyl elaidate.

Aroma components of Cephalanthera orchids.

The SPME-GC-MS analysis of the aroma components of Cephalanthera damasonium, Cephalanthera rubra, and Cephalanthera longifolia were reported. The main components found in C. damasonium were pentadecane, hexadecane, heptadecane and α-farnesene. The same compounds were found in the scent of C. rubra. Although C. damasonium and C. rubra have different pollination mechanisms, their spectrum of volatile compounds surprisingly does not differ significantly. In C. longifolia pentadecane and heptadecane were found together with cis-ß-farnesene. As C. longifolia is allogamous, the differences in scent composition may play a role in pollinator attraction.

Paternò-Büchi reaction between furan and heterocyclic aldehydes: oxetane formation vs. metathesis.

The photochemical reaction of 2-substituted heterocyclic aldehydes with furan gave the corresponding exo oxetane derivatives through the excited triplet state. However, in situ the oxetane derivatives were converted through a metathesis reaction into the corresponding Z,E-butadienyl formate derivatives. On the contrary, 3-substituted heterocyclic aldehydes gave the corresponding exo oxetane derivatives. The effect of 2-substituted heterocyclic ring in order to facilitate the metathesis reaction is explained considering the possible participation of the pi aromatic orbitals in the oxetane C-O bond cleavage.

High temperature treatment allows the detection of episesamin in paulownia wood extractives.

The composition and the relative variation of secondary metabolites of Paulownia tomentosa S. wood under thermal effect is a little explored area. Wood material was previously thermo-treated at 210 °C for 3 hours using a press vacuum technology. Extractives of untreated and thermo-treated wood material achieved with Soxhlet extraction techniques were obtained. Then the extracts were chromatographed by using thin layer chromatography. Component groups in extracts were determined by gas chromatography in combination with mass spectrometry. In terms of wood change the thermo-treatment of wood induces a darkening of wood color surface (ΔL* = 28.3), an increase of mass loss (3.5%) and an increase of the amount of extractives and lignin content as well as an increase of the chloroform soluble fraction. This work mainly describes the chemical exploration of the extract from paulownia wood, leading to the isolation and identification of episesamin.

Fragrance components of Platanthera bifolia subsp. osca and Platanthera chlorantha collected in several sites in Italy.

Platanthera bifolia subsp. osca sample collected at Grisolia showed as main components linalool (17.8%), benzyl benzoate (55.8%), and benzyl 2-hydroxybenzoate (6.7%). Four samples of P. bifolia subsp. osca were collected at Pignola: the main components of the aroma are lilac derivatives (49.02-79.00%), mainly lilac alcohols B (7.41-13.52%), C (10.10-18.45%), and D (7.50-34.28%). Three samples were analyzed from the site of Marsico Nuovo. The main components of the scent found in this site were linalool (1.54-10.00%), lilac aldehydes (3.98-11.15%), and mainly lilac alcohols (50.68-61.51%). The main components of the sample collected at Palena were methyl benzoate (9.04%) and benzyl benzoate (74.72%). The analysis of the composition of the aroma of a Platanthera chlorantha plant has been performed. The main components were lilac derivatives. The reported behavior could be explained admitting an adaptive modification of the scent considering the nature of possible pollinating agents due to different habitats.