Ishmael B. Masesane

Reactions of salicylaldehyde and enolates or their equivalents: versatile synthetic routes to chromane derivatives

Summary The reported methodologies for the synthesis of chromane derivatives through the reaction of salicylaldehyde and enolates are discussed. The enolates and their equivalents involved in the reactions discussed in this article were derived from ketones, nitroalkanes, malononitrile and α,β-unsaturated compounds.

The oxanorbornene approach to 3-hydroxy, 3,4-dihydroxy and 3,4,5-trihydroxy derivatives of 2-aminocyclohexanecarboxylic acid

The nitro oxanorbornene adduct derived from the Diels-Alder reaction of ethyl (E)-3-nitroacrylate and furan provides a versatile template for the stereoselective synthesis of hydroxylated derivatives of 2-aminocyclohexanecarboxylic acid (ACHC).

Tylosema esculentum extractives and their bioactivity

The investigation of Tylosema esculentum (Morama) husks, cotyledons, and tuber yielded griffonilide 2, compound 1, griffonin 3, gallic acid 4, protocatechuic acid 5, β-sitosterol 6, behenic acid 7, oleic acid 8, sucrose 9, 2-O-ethyl-α-D-glucopyranoside 10, kaempferol 11 and kaempferol-3-O-β-D-glucopyranoside 12. The structures of the isolates were determined by NMR, HR-TOF EIMS, IR and UV-vis spectroscopy, and by comparison with literature data. The husk EtOAc and n-butanol extracts demonstrated >90% DPPH radical scavenging activity at concentrations of 25, 50 and 250 μg/mL. Furthermore the husk extracts showed higher total phenolic content (233 mg GAE/g). The extractives exhibited minimum inhibitory quantities of 50-100 μg or no activity against Staphylococcus aureus, Escherichia coli, Bacillus subtilis, Pseudomonas aeruginosa and Candida albicans. The tuber extracts were inactive against Caco-2 and Hela cell lines, while the husk extracts showed low activity against Caco-2 and Vero cell line with IC(50) values >400 μg/mL. The GC-MS analysis showed the beans and tuber non-polar (n-hexane) extracts major constituents as fatty acids.

From nature, through chemical synthesis, toward use in agriculture: Oryzoxymycin case study

The Diels-Alder adducts of ethyl (E)-3-nitroacrylate and furan provided a common and versatile template for the stereocontrolled synthesis of an isomer of the natural product oryzoxymycin and polyhydroxylated cyclohexyl β-amino acid derivatives. The strategy for the synthesis of the polyhydroxylated cyclic β-amino acid derivatives involved base-induced fragmentation of the oxanorbornene skeleton and face selective oxidation reactions. A Pd-catalyzed transfer hydrogenation reaction in the presence of organic acids is also described. This reaction is amenable to being enantioselective through use of optical pure chiral organic acids.

Flavanones of Erythrina livingstoniana with antioxidant properties

Six new flavanones (1-6), together with six known compounds were isolated from Erythrina livingstoniana. Their structures were elucidated on the basis of NMR data and HRMS(n) fragmentation pathway and by comparison with literature data. Compounds 5, 7 and 8 showed remarkable DPPH free radical scavenging efficacies. The compounds, however, did not demonstrate an anti-inflammatory potential when tested using a PGE2 (prostaglandin E2) competitive enzyme immunoassay. The plausible biosynthetic pathways of the isolated compounds are described.

A sensitive LC-MS/MS method employing a THF–water solvent system for the determination of chloramphenicol, thiamphenicol and florfenicol in bovine muscle

A THF–water solvent system was used in the development of a method for the LC-MS/MS determination of chloramphenicol (CAP), thiamphenicol (TAP) and florfenicol (FFC) in bovine muscle. The tetrahydrofuran (THF)–water solvent system was recently demonstrated to possess superior figures of merit compared to either the methanol–water or acetonitrile–water solvent systems which are almost exclusively used in LC-MS for the determination of fenicols in food producing animals. The figures of merit included ease of de-solvation when electrospray ionization (ESI) is employed in the negative mode thus leading to more intense mass spectral signals. This phenomenon was shown to be due to greater association of the methyl groups in methanol or acetonitrile with the amide nitrogen common in all the three fenicols. This association is absent in a THF–water solvent system since it is devoid of methyl groups that can easily interact with the amide nitrogen. As a result of the use of the THF–water solvent system, the method detection limits (MDLs) were 0.047, 2.1 and 4.3 μg kg−1 for CAP, TAP and FFC respectively while the limits of quantitation were 0.141, 6.3 and 12.9 μg kg−1 for CAP, TAP and FFC respectively. The decision limits i.e. CCα values according to the Commission Decision 2002/657/EC criteria were 0.36, 50 and 111 μg kg−1 for CAP, TAP and FFC respectively. Linearities were also within acceptable values i.e. 0.9983, 0.9916 and 0.9996 for CAP, TAP and FFC respectively.

Efficient and Green Preparation of 2-Amino-4H-chromenes by a Room-Temperature, Na2CO3-Catalyzed, Three-Component Reaction of Malononitrile, Benzaldehydes, and Phloroglucinol or Resorcinol in Aqueous Medium

Abstract The preparation of substituted 2-amino-4H-chromenes by a Na2CO3-catalyzed reaction of malononitrile, benzaldehydes, and phloroglucinol or resorcinol in aqueous medium and at room temperature is reported. The merits of this procedure include limited use of organic solvents, easy workup technique, and high purity of products. The 2-amino-4H-chromenes were prepared in yields of 54–96%. GRAPHICAL ABSTRACT

A flavanone and antimicrobial activities of the constituents of extracts from Mundulea sericea.

In this study, 12 compounds, which include a new flavanone 5-methoxy mundulin (1), were isolated from the leaves, stem bark and twigs of Mundulea sericea (Willd.) A. Chev. (Fabaceae; Papilionoideae). The structures of the compounds were identified based on spectral data analyses. The constituents of M. sericea also showed antimicrobial activities (MIQ = 0.01–100 µg) against Staphylococcus aureus, Bacillus subtilis, Escherichia coli, Pseudomonas aeruginosa and Candida albicans.

Fast and efficient synthesis of flavanones from cinnamic acids

ABSTRACT A fast and efficient synthesis of flavanones from cinnamic acids in three steps has been developed. First, the cinnamic acid was converted to cinnamyol chlorides using SOCl2. The acid chlorides were then treated with substituted phenols in BF3 · OEt2 to furnish corresponding chalcones in 42(75% yields. Base-catalyzed cyclization of the chalcones at room temperature afforded corresponding flavones in 85–95% yields. The conversion of the cinnamic acid derivatives to corresponding chalcones was found to be sensitive to the position and nature of the substituents on the aromatic rings. GRAPHICAL ABSTRACT

Comparative Review of the Synthesis of Flavanones via the Reaction of Cinnamic Acids and Phenols and the Reaction of 2-Hydroxyacetophenones and Benzaldehydes

This review compares the efficiency of a three-step procedure developed by the authors for the synthesis of flavanones that relied on the boron trifluoride diethyl etherate (BF3·OEt2)-mediated reaction of cinnamic acid and phenols to the one-step or two-step procedures reported in literature involving the reaction of 2-hydroxyacetophenones and benzaldehydes. The three-step procedure was found to give the flavanones in comparable yields to both the one-step and the two-step literature methods.