Polyenyl cations and radical cations – synthesis, spectroscopic properties and reactions

In the present work, polyene precursors for the formation of charged polyenyl species were synthesised. Their conversion to charge delocalised radical cations and diamagnetic mono- and dications was carried out by treatment with Brønsted and Lewis acids. Reaction conditions were optimised to achieve sufficient stability of the charged polyenes for characterisation by modern spectroscopic methods; in particular nearinfrared absorption spectroscopy (NIR), two-dimensional nuclear magnetic resonance (2D NMR), electron paramagnetic resonance (EPR) and dynamic light scattering. The full assignment of 13C NMR chemical shifts of mono- and dications was used as basis for charge distribution estimates in charge delocalised polyenes. Coulombic repulsions are dominant features in dicationic systems, whereas monocations show a more even distribution of charge throughout the polyene system. The size limit of charge delocalisation regions, suggested by current theories, has been investigated using an empirical approach. Treatment of the cationic polyenes with nucleophiles gave conversion to neutral compounds, which were characterised by mass spectrometry (MS) and ultraviolet/ visible absorption spectroscopy (UV/Vis), in addition to NMR. In most cases, theidentified neutral compounds supported the structural characterisation of their charged precursors. The work is of relevance to the classical blue colour reactions of polyenes developed in the early 20th century. The chemistry behind these reactions has previously not been elucidated. Only during the last 15-20 years has the instrumental methods necessary for the study of this chemistry been available. In current studies on the colouration mechanism of the carotenoproteins present in external tissues of some marine organisms, a polarisation of the polyene chain appear to be of importance. Moreover, radical cations of polyenes are unstable intermediates in Nature, where they are shown to be of importance in photosynthetic processes in green plants and bacteria. The delocalised polyenylic cations studied here, representing a new direction of structural studies in the carotenoid/retinoid field, are of interest in a wider context for carbocation structure and stability in basic organic chemistry and the various applied aspects outlined above

Quantification of Fatty Acids and their Regioisomeric Distribution in Triacylglycerols from Porcine and Bovine Sources Using 13C NMR Spectroscopy

The uptake of specific fatty acids in humans is dependent on their position on the glycerol backbone. There is a great interest in methods that can access this information fast and accurately. By way of high‐resolution NMR, we have analyzed TAG extracted from pig and beef tissues and obtained quantitative data for the composition and regioisomeric distribution of all major unsaturated fatty acids usually found in these source materials, using a combination of manual integration and deconvolution of 13C NMR spectra. In addition, we have developed a method for determining composition and regioisomeric distribution of the two main saturated fatty acids found in pork (16:0, 18:0). The results are discussed in relation to species‐specific genetic characteristics of fatty acid and TAG biosynthesis. The developed method could support decisions related to breeding for desired fatty acid profiles, and stimulate further methodology developments using high field NMR

Quantification of Fatty Acids and their Regioisomeric Distribution in Triacylglycerols from Porcine and Bovine Sources Using 13C NMR Spectroscopy

The uptake of specific fatty acids in humans is dependent on their position on the glycerol backbone. There is a great interest in methods that can access this information fast and accurately. By way of high-resolution NMR, we have analyzed TAG extracted from pig and beef tissues and obtained quantitative data for the composition and regioisomeric distribution of all major unsaturated fatty acids usually found in these source materials, using a combination of manual integration and deconvolution of 13C NMR spectra. In addition, we have developed a method for determining composition and regioisomeric distribution of the two main saturated fatty acids found in pork (16:0, 18:0). The results are discussed in relation to species-specific genetic characteristics of fatty acid and TAG biosynthesis. The developed method could support decisions related to breeding for desired fatty acid profiles, and stimulate further methodology developments using high field NMR

Compound "J'' in Late Cretaceous/Tertiary terrigenous oils revisited: Structure elucidation of a rearranged oleanane coeluting on GC with 18 beta(H)-oleanane

A C-30 pentacyclic triterpane eluting slightly after 18 alpha(H)-oleanane in the m/z 191 mass chromatograms of Late Cretaceous/Tertiary terrigenous oils (peak "J'' in the early literature) has been isolated from a Niger Delta oil and identified using NMR spectroscopy as 3 beta-methyl-24-nor-18 alpha(H)-oleanane. The previous assignment as 18 beta(H)-oleanane is therefore partly erroneous. 3 beta-Methyl-24-nor-18 alpha(H)-oleanane affords a larger m/z 412 - gt 356 response than the oleananes and the relative contribution of 3 beta-methyl-24-nor-18 alpha(H)-oleanane to the 412 - gt 191 "oleanane peak'' can be roughly estimated from comparison of the 412 - gt 356/412 - gt 191 ratio from the oleanane peak with that of the pure compounds. 3 beta-Methyl-24-nor-18 alpha(H)-oleanane can be as abundant as 18a(H)-oleanane in oils having a high concentration of early eluting rearranged oleananes. 3 beta-Methyl-24-nor-19 alpha(H)-taraxastane was also tentatively assigned in the oils on the basis of its mass spectrum as well as its gas chromatography and high performance liquid chromatography retention times. 3 beta-Methyl-24-nor-gammacerane was tentatively assigned in a similar way in an oil containing gammacerane. All 3 beta-methyl-24-nor-triterpanes could be formed via dehydration, rearrangement and hydrogenation of triterpenoids having an OH group at C-3. (C) 2014 Elsevier Ltd. All rights reserved

Identification of a Novel Series of Benzohopanes and Their Geochemical Significance

series of novel C-33-C-35 hexacyclic benzohopanes (C(33)b-C(35)b) were identified in 39 samples of coal extracts and 39 crude oils of different ages from all over the world. C(33)b and C(34)b homologues were isolated, and their structures were determined by nuclear magnetic resonance. The structure of C(35)b benzohopane was proposed based on the mass spectrum and its similarity with the mass spectra of structurally defined C(33)b and C(34)b homologues. The structures of the C(33)b-C(35)b hexacyclic benzohopanes are closely related to isohopanes; both groups are typical for terrestrial organic matter and can be useful in the correlation analysis. A possible pathway of formation of these novel benzohopanes and their hopanoid precursors with an additional branch in the aliphatic side chain is proposed. C(33)b-C(35)b hexacyclic benzohopanes are stable up to the maturity level corresponding to random vitrinite reflectance (Rr) of similar to 0.80%, which was demonstrated by analyzing the samples of different maturity and by the maturation simulation experiments: hydrous pyrolysis of two bituminous coals (Rr = 0.55 and 0.59%) and pyrolysis of an extracted bituminous coal (Rr = 0.56%) and its asphaltenes. This represents a confirmation that the formation of these novel benzohopanes is related to specific depositional conditions and microbial activity during diagenesis. Mature samples (Rr = 0.8%) and hydrous pyrolysate of the bituminous coals (Rr lt 0.60%) obtained at 330 degrees C show a distinct distribution of benzohopanes in comparison to immature and moderately mature samples, which is characterized by a low abundance of the b series benzohopanes and the presence of regular and numerous other benzohopane isomers. The latter most likely represent isomers of regular and novel benzohopanes with different substitution patterns on the aromatic ring. This isomerization of alkyl groups attached to the aromatic ring, leading to the formation of thermodynamically more stable isomers, is a well-known maturation scenario so far reported in the series of alkylated naphthalenes, phenanthrenes, and dibenzothiophenes. Therefore, in the same way, a distribution of benzohopanes can indicate thermal maturity. In addition to the novel benzohopanes, three series (2 alpha, 2 beta, and 3 beta) of their methylated derivatives were identified in numerous samples. Finally, a novel C-35 heptacyclic benzohopane with an additional cyclopentane ring was also observed in the studied samples, and its structure was tentatively identified based on the mass spectrum. Opposite to the hexacyclic C(33)b-C(35)b benzohopanes, the formation of the C-35 heptacyclic benzohopane does not require a specific hopanoid precursor with two branches in the side chain. Therefore, this compound seems to have less geochemical significance than the new hexacyclic benzohopanes

Dehydroicetexanes in sediments and crude oils: Possible markers for Cupressoideae

Two previously unidentified dehydroabietane isomers were isolated from Miocene Serbian lignite and Rhaetian (Late Triassic) coaly mudstones from South Sweden and characterized using NMR-spectroscopy as cis- and trans-dehydroicetexane. Both have a 9(10→20)-abeo-abietane or icetexane skeleton consisting of a 6-7-6 tricyclic framework with seven carbons in ring B instead of the usual six in common diterpanes of the abietane-type. Dehydroicetexanes can be detected using GC-MS-MS in m/z 270 → 146 chromatograms without interference from dehydroabietane or other isomers. Dehydroicetexanes are often abundant in high latitude coals and mudstones ranging fromTriassic to Miocene, and in high latitude oils (Canada and Greenland) sourced from terrigenous organic matter. The trans/(cis+ trans) dehydroicetexane ratio is low in immature sediments, but usually around 0.83 in oils and mature sediments with vitrinite reflectance (%Rr) above 0.5 suggesting an equilibrium from the start of the oil window. Dehydroicetexanes are more stable than dehydroabietane and some oils, rich in dehydroicetexanes, contain no dehydroabietane. Precursors could be plant diterpenoids having the icetexane structure, which have been known for more than 40 years and isolated from a variety of higher plant sources, including some angiosperms. Many of the relatively simple icetexanes were isolated for the first time from Chamaecyparis pisifera and related species where they seem to be particularly abundant, suggesting that dehydroicetaxanes may be used as markers for the genus Chamaecyparis or for Cupressoideae in general.This is the peer-reviewed version of the following article: Nytoft, H. P.; Kildahl-Andersen, G.; Lindström, S.; Rise, F.; Bechtel, A.; Mitrović, D.; Đoković, N.; Životić, D.; Stojanović, K. A. Dehydroicetexanes in Sediments and Crude Oils: Possible Markers for Cupressoideae. Organic Geochemistry 2019, 129, 14–23. [https://doi.org/10.1016/j.orggeochem.2019.01.001

Synthesis and biological evaluation of zinc chelating compounds as metallo-β-lactamase inhibitors

International audienceThe syntheses of metallo-β-lactamase inhibitors comprising chelating moieties, with varying zinc affinities,and peptides partly inspired from bacterial peptide sequences, have been undertaken. The zinc chelatorstrength was varied using the following chelators, arranged in order of ascending binding affinity:dipicolylamine (DPA, tridentate), dipicolyl-1,2,3-triazolylmethylamine (DPTA, tetradentate) dipicolyl ethylenediamine(DPED, tetradentate) and trispicolyl ethylenediamine (TPED, pentadentate). The chosen peptideswere mainly based on the known sequence of the C-terminus of the bacterial peptidoglycan precursors.Biological evaluation on clinical bacterial isolates, harbouring either the NDM-1 or VIM-2 metallo-β-lactamase, showed a clear relationship between the zinc chelator strength and restoration of meropenemactivity. However, evaluation of toxicity on different cancer cell lines demonstrated a similar trend, and thusinclusion of the bacterial peptides did possess rather high toxicity towards eukaryotic cells