The chemical reactivity of cannabidiol is based on its ability to undergo intramolecular cyclization driven by the addition of a phenolic group to one of its two double bonds. The main products of this cyclization are Δ9-THC (trans-Δ-9-tetrahydrocannabinol) and Δ8-THC (trans-Δ-8-tetrahydrocannabinol). These two cannabinoids are isomers, and the first one is a frequently investigated psychoactive compound and pharmaceutical agent. The isomers Δ8-iso-THC (trans-Δ-8-iso-tetrahydrocannabinol) and Δ4(8)-iso-THC (trans-Δ-4,8-iso-tetrahydrocannabinol) have been identified as additional products of intramolecular cyclization. The use of Lewis and protic acids in different solvents has been studied to investigate the possible modulation of the reactivity of CBD (cannabidiol). The complete NMR spectroscopic characterizations of the four isomers are reported. High-performance liquid chromatography analysis and 1H NMR spectra of the reaction mixture were used to assess the percentage ratio of the compounds formed.
Resource partitioning has been intensely studied in fish assemblages of tropical reefs, whereas surprisingly little research has been conducted on the benthic Mediterranean. Here we describe the composition of a fish assemblage of the rocky slopes at Tremiti Islands, southern Adriatic Sea, the vertical distribution at depths from 0 to 42 m, habitat choice and food use of the different species, and we identify the resources along which species are ecologically segregated. Species composition and fish density showed high similarities with the few other assemblages that have been censused on the rocky coasts of the Mediterranean. We observed a wide overdispersion among species in their use of food and habitat, while very little segregation occurred at the level of depth distribution. No coincident use of food, habitat or active periods occurred among fish species, and no trophic guilds exist in the threedimensional niche. ProblemBenthic euphotic zones have high primary production and a wide structural heterogeneity. These factors diversify microhabitats and promote rich animal communities, which are particularly suitable for studies of community structure and resource partitioning. The shallow benthic Mediterranean includes three main biocoenoses: sand flats, seagrass beds and rocks. The latter can be further divided into rocky bottoms with variously sized blocks and into rocky slopes, where the concretions of algae and of other organisms with calcareous skeletons create a high structural complexity .
In the past few decades natural and non-natural prolines-and among the latter, a-quaternary derivatives are of great interest-have found wide application in the design of new organocatalysts [1] and chiral auxiliaries [2] for asymmetric synthesis. Furthermore, non-natural proline units have been incorporated in new peptide chains, affording peptidomimetics with different conformational flexibility and correlated drastic changes of their secondary structures. [3] In the best cases, these alterations enhance the resistance of the modified proteins to metabolic and chemical degradation and hence their overall biological activity.A number of strategies [4] -and, among them, those that adopt the well-known Kawabatas principles of "memory of chirality" (MOC) [5] and of "chiral non-racemic enolate" [6] emerge as the most appealing-have been proposed for the stereoselective synthesis of quaternary a-amino acids. In particular, the synthetic methods for quaternary prolines [7] involve the enantioselective functionalization of l-proline derivatives, for example, through self-reproduction of chirality, diastereoselective alkylation, or transfer of stereochemical information via cyclic ammonium ylides.Recently, we reported a straightforward protocol for the enantioselective synthesis of quaternary N-alkyl-a-4-nitrophenyl-a-amino tert-butyl esters, through N-alkylation of the corresponding a-N-(4-nitrophenyl)sulfonamido esters, followed by degradative rearrangement, with loss of SO 2 .[8]The one-pot overall process is highly stereoselective, ees up to 98 %; in contrast, the reaction conducted with the preformed N-alkyl-a-N-(4-nitrophenyl)sulfonamido ester gave the corresponding quaternary amino ester with very low ees, for example, 28 % ee in the case of N-allyl phenylalanine derivative. In the present paper we describe the rearrangement under basic conditions of N-(arylsulfonyl)proline tert-butyl esters 1, which showed a different behavior of that found for N-alkylated open-chain sulfonamido esters. Preliminary runs (Table 1), conducted on N-(4-nitrobenzenesul-[a] F.
Phase-transfer catalysis (PTC) is a well-known useful tool to develop sustainable processes. Benefits deriving from using PTC are particularly evident in oxidation chemistry where it has been possible to replace many toxic, aggressive reagents with harmless and milder oxidants such as bleach or hydrogen peroxide.
The 'one-pot' stereoselective conversion of N-(4-nitrobenzene)sulfonyl-alpha-amino acid tert-butyl esters into the corresponding N-alkyl-alpha-(4-nitrophenyl)-alpha-amino esters has been realized through N-alkylation of the starting amido esters, followed by N-C(alpha) migration of the p-nitrophenyl group and the loss of sulfur dioxide; the asymmetric induction is determined by an intermediate non-racemic enolate, without the need of an external source of chirality.
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