Extraction, Purification, Quantification, and Stability of Bioactive Spilanthol from Acmella oleracea.

Acmella oleracea is an ethnobotanically significant plant with a relatiwely high content of spilanthol. Due to its broad spectrum of activity, including anti-inflammatory, antioxidant, analgesic, antifungal, and bacteriostatic properties, it is considered a valuable bioactive natural product. In addition, spilanthol as its main bioactive component inhibits facial muscle contractions, making it an attractive ingredient in anti-wrinkle and anti-aging cosmetics. Due to its muscle paralyzing effects, it is called herbal botox. The commercial interest in spilanthol encourages the development of effective methods of isolating it from plant material. The methodology used in this paper allows for the obtaining of extracts from Acmella oleracea with a relatively high content of spilanthol. An effective method of spilanthol extraction from all aerial parts of Acmella oleracea as well as methods of enriching spilanthol concentration in extracts achieved by removing polar and acidic substances from crude extracts was developed. To quantify the concentration of spilanthol, a simple, fast and economically feasible quantification protocol that uses nuclear magnetic resonance (HNMR) was developed. In addition, it has been proven, that oxidation of spilanthol by air gives (2E,7Z)-6,9-endoperoxy-N-(2-methylpropyl)-2,7-decadienamide. The studies on spilanthol solutions stability were carried out and the conditions for the long-time storage of spilanthol solutions have also been developed. Additionally, for confirmation of obtained results a sensitive (LOQ=1 ng/mL), precise (RSD lower than 7%) and accurate (RE lower than 7.5%), new HPLC-MS/MS method was applied.

Generation and Reactivity of 1-Imidocarbenium Cations in the Friedel-Crafts-type Reaction.

Herein, we discuss the formation and reactivity of 1-imidocarbenium cations in Friedel-Crafts-type reaction between 1-imidoalkylphosphonium salts and arenes. The observed weakening of Cα-P+ bond is described qualitatively and quantitatively. The determination of rate constants and activation energies of Cα-P+ bond cleavage enabled systematic reactivity investigations of a series of phosphonium salts with different structures. Finally, the application scope for the imidoalkylation of aromatic hydrocarbons was explored. The results confirm that the generated 1-imidocarbenium cations are reactive enough to alkylate strongly activated, less-activated, or even inactivated aromatic compounds.

1-Imidoalkylphosphonium salts with modulated Cα-P+ bond strength: synthesis and application as new active α-imidoalkylating agents.

An effective synthesis of the hitherto unknown 1-imidoalkylphosphonium salts has been developed in the reported study. The crucial step in the method included the decarboxylative α-methoxylation of N-phthaloyl- or N-succinylamino acids to the corresponding N-(1-methoxyalkyl)imides, followed by the displacement of the methoxy group by the triarylphosphonium group through melting of the imide derivative with triarylphosphonium tetrafluoroborate. The imidoalkylating properties of the obtained 1-imidoalkylphosphonium salts were tested using the Tscherniac-Einhorn-type reaction with aromatic hydrocarbons as a model reaction. It was found that the Cα-P+ bond strength can be considerably reduced and the imidoalkylation of arenes can be markedly facilitated using 1-imidoalkylphosphonium salts derived from triarylphosphines with electron-withdrawing substituents such as tris(m-chorophenyl)phosphine, tris(p-chlorophenyl)phosphine and tris[p-(trifluoromethyl)phenyl]phosphine. Microwave irradiation also considerably facilitates the cleavage of the highly polar Cα-P+ bond.

Vinylphosphonium and 2-aminovinylphosphonium salts - preparation and applications in organic synthesis.

The main synthetic routes towards vinylphosphonium salts and their wide applications in organic synthesis are discussed in this review. Particular attention is paid to the use of these compounds as building blocks for the synthesis of carbo- and heterocyclic systems after their prior transformation into the corresponding phosphorus ylides, followed by the intramolecular Wittig reaction with various types of nucleophiles containing a carbonyl function in their structures.

A new method for the synthesis of α-aminoalkylidenebisphosphonates and their asymmetric phosphonyl-phosphinyl and phosphonyl-phosphinoyl analogues.

A convenient approach has been developed to α-aminoalkylidenebisphosphonates and their asymmetric phosphonyl-phosphinyl and phosphonyl-phosphinoyl analogues by α-phosphonylation, α-phosphinylation or α-phosphinoylation of 1-(N-acylamino)alkylphosphonates, that, in turn, are easily accessible from N-acyl-α-amino acids. Effective electrophilic activation of the α-position of 1-(N-acetylamino)alkylphosphonates was achieved by electrochemical α-methoxylation of these compounds in methanol, mediated with NaCl, followed by displacement of the methoxy group with triphenylphosphonium tetrafluoroborate to give hitherto unknown 1-(N-acetylamino)-1-triphenylphosphoniumalkylphosphonate tetrafluoroborates. The latter compounds react smoothly with trialkyl phosphites, dialkyl phosphonites or alkyl phosphinites in the presence of Hünig's base and methyltriphenylphosphonium iodide in a Michaelis-Arbuzov-like reaction to give the expected alkylidenebisphosphonates, 1-phosphinylalkylphosphonates or 1-phosphinoylalkylphosphonates, respectively, in good yields.

1-(N-acylamino)alkyl sulfones from N-acyl-α-amino acids or N-alkylamides.

A variety of N-(1-methoxyalkyl)amides or carbamates react readily with sodium aryl sulfinates in the presence of triphenylphosphonium tetrafluoroborate or bromide in CHCl3 under mild conditions to give 1-(N-acylamino)alkyl sulfones in good yields. A combination of this reaction with the recently described electrochemical decarboxylative α-methoxylation of N-acyl-α-amino acids to give N-(1-methoxyalkyl)amides in the presence of 3-(1-piperidino)propyl-functionalized silica gel (SiO2-Pip) enables an effective two-pot transformation of N-acyl-α-amino acids to 1-(N-acylamino)alkyl sulfones. Alternatively, N-(1-methoxyalkyl)amides can be obtained by electrochemical α-methoxylation of either N-alkylamides, lactams, or N-alkylcarbamates.

α-Amidoalkylating agents from N-acyl-α-amino acids: 1-(N-acylamino)alkyltriphenylphosphonium salts.

N-Acyl-α-amino acids were efficiently transformed in a two-step procedure into 1-N-(acylamino)alkyltriphenylphosphonium salts, new powerful α-amidoalkylating agents. The effect of the α-amino acid structure, the base used [MeONa or a silica gel-supported piperidine (SiO(2)-Pip)], and the main electrolysis parameters (current density, charge consumption) on the yield and selectivity of the electrochemical decarboxylative α-methoxylation of N-acyl-α-amino acids (Hofer-Moest reaction) was investigated. For most proteinogenic and all studied unproteinogenic α-amino acids, very good results were obtained using a substoichiometric amount of SiO(2)-Pip as the base. Only in the cases of N-acylated cysteine, methionine, and tryptophan, attempts to carry out the Hofer-Moest reaction in the applied conditions failed, probably because of the susceptibility of these α-amino acids to an electrochemical oxidation on the side chain. The methoxy group of N-(1-methoxyalkyl)amides was effectively displaced with the triphenylphosphonium group by dissolving an equimolar amount of N-(1-methoxyalkyl)amide and triphenylphosphonium tetrafluoroborate in CH(2)Cl(2) at room temperature for 30 min, followed by the precipitation of 1-N-(acylamino)alkyltriphenylphosphonium salt with Et(2)O.

1H NMR spectroscopic criteria for the configuration of N-acyl-alpha,beta-dehydro-alpha-amino acid esters.

The diagnostic values of the following three spectral criteria for the configuration of N-acyl-alpha,beta-dehydro-alpha-amino acid esters were examined: (i) the proton at the beta-position at the double bond of a Z-isomer is shielded if compared with the respective E-isomer (delta(beta)Z < delta(beta)E); (ii) the proton at the nitrogen atom is shielded in a Z-isomer in comparison with the corresponding E-isomer (delta(NH)Z < delta(NH)E); and (iii) changing of the solvent from CDCl3 to deuterated trifluoroacetic acid (TFA) causes shielding of the H(beta) vinylic proton of an E-isomer or deshielding of the respective proton of the Z-isomer (delta(CDCl3)E > delta(TFA)E or delta(CDCl3)Z < delta(TFA)Z). The investigations were based on a set of 22 (Z)- and (E)-N-acyl-alpha,beta-dehydro-alpha-amino acid esters of diverse structures, with aliphatic, aromatic and heteroaromatic substituents at the vinylic beta-carbon; most of the examined compounds were hitherto unknown. The application of the substituent effect additivity rule given by Pascual et al. for olefinic protons leads to evidently erroneous configuration assignments of N-acyl-alpha,beta-dehydro-alpha-amino acid esters. The considered criteria were fulfilled for all the examined cases with one exception [the second criterion for the alpha-pivaloylamino-beta-(2-furyl)acrylates]. The comparison of changes in the chemical shifts of H(beta) vinylic protons in CDCl3 and deuterated TFA seems to be the most reliable and useful configuration criterion, as it can be used in the case of a single isomer.