Synthesis and biological activity of arylspiroborate salts derived from caffeic Acid phenethyl ester

Preliminary investigations into the synthesis and antimicrobial activities of boron-containing capsaicinoids

This preliminary study reports on the synthesis of two new boron-capsaicin derivatives containing either a short or long chain aliphatic tail group using an iridium catalyzed hydroboration reaction with pinacolborane. The boronate ester groups reside on the terminal position of the tail group and are necessary for the bioactivity of these compounds. Indeed, both compounds showed considerable activity against two Gram-positive bacteria, including Vancomycin-resistant Enterococcus. Vancomycin is considered the last resort medication for the treatment of septicemia, and new antibacterial agents that can treat sepsis are of paramount importance. The more lipophilic boron compound with the longer aliphatic chain also showed antifungal activity against Saccharomyces cerevisiae.

Structural and biological overview of Boron-containing amino acids in the medicinal chemistry field

Amino acids are the basic structural units of proteins as well as the precursors of many compounds with biological activity. The addition of boron reportedly induces changes in the chemical-biological profile of amino acids.

METHODS

We compiled information on the biological effect of some compounds and discuss the structure-activity relationship of the addition of boron. The specific focus presently is on borinic derivatives of α-amino acids, the specific changes in biological activity caused by the addition of a boron-containing moiety, and the identification of some attractive compounds for testing as potential new drugs.

RESULTS

Borinic derivatives of α-amino acids have been widely synthesized and tested as potential new therapeutic tools. The B-N (1.65 A°) or B-C (1.61 A°) or B-O (1.50 A°) bond is often key for the stability at different pHs and temperatures and activity of these compounds. The chemical features of synthesized derivatives, such as the specific moieties and the logP, polarizability and position of the boron atom are clearly linked to their pharmacodynamic and pharmacokinetic profiles. Some mechanisms of action have been suggested or demonstrated, while those responsible for other effects remain unknown.

CONCLUSION

The increasing number of synthetic borinic derivatives of α-amino acids as well as the recently reported crystal structures are providing new insights into the stability of these compounds at different pHs and temperatures, their interactions on drug targets, and the ring formation of five-membered heterocycles. Further research is required to clarify the ways to achieve specific synthesis, the mechanisms involved in the observed biological effect, and the toxicological profile of this type of boron-containing compounds (BCCs).

Crystal structure of pyridinium bis(naphthalane-2,3-diolato-κ2 O,O′)borate monohydrate, C25H20BNO5

C25H20BNO5, triclinic, P1̅ (no. 2), a = 7.0868(6) Å, b = 10.3522(6) Å, c = 15.3140(10) Å, α = 74.088(7)°, β = 89.996(7)°, γ = 79.190(1)°, V = 1059.71(13) Å3, Z = 2, R gt(F) = 0.0445, wR ref(F 2) = 0.1105, T = 298 K.

Fabrication of Novel Bioactive Cellulose-Based Films Derived from Caffeic Acid Phenethyl Ester-Loaded Nanoparticles via a Rapid Expansion Process: RESOLV

Caffeic acid phenethyl ester (CAPE) nanoparticles (NPs) with an average size of ∼40 nm obtained from TEM and binomial average sizes of ∼90 and ∼400 nm obtained from DLS were successfully produced by rapid expansion of subcritical solutions into liquid solvents (RESOLV). The minimum inhibitory concentrations (MICs) and minimum bactericidal concentrations (MBCs) of CAPE and CAPE-NPs were determined by plate count method against 12 pathogenic and spoilage bacteria and 3 strains of yeast. Total phenolic content (TPC) and antioxidant activities of CAPE-NPs were quantified and subsequently investigated using two assays, including 2,2-diphenyl-1-picrylhydrazyl (DPPH) radical scavenging and ferric reducing antioxidant power (FRAP). CAPE-NP-incorporated cellulose-based films were prepared and characterized. MICs and MBCs of CAPE-NPs against most bacteria and Candida albicans were 700 and 1400 μg/mL, respectively. CAPE-NPs yielded a TPC value of 426.74 μgGAE/mg and lower antioxidant activities than those of CAPE in ethanol (CAPE-EtOH), whereas BHT yielded lower FRAP than that of CAPE-NPs. The impregnation of CAPE into cellulose-based films was confirmed by FTIR spectra. Moreover, incorporation of only 0.5 wt % CAPE-NPs into the films resulted in an inhibitory effect against microorganisms. Fortunately, incorporation of higher concentration of CAPE-NPs-MC films led to a significantly higher antioxidant activity and vice versa. This indicated that CAPE-NPs significantly enhanced the antimicrobial and antioxidant activities of CAPE. The results show that the environmentally benign supercritical CO2 technique should be generally applicable to NP fabrication of other important bioactive ingredients, especially in liquid form. In addition, it is suggested that CAPE-NPs can be used to reduce the dosage of CAPE and improve their bioavailability and thus merit further investigation for bioactive packaging film and coating applications.