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Substrate specificity of chalcone synthase from Petroselinum hortense. Formation of phloroglucinol derivatives from aliphatic substrates.

The substrate specificity of chalcone synthase, the key enzyme of flavonoid biosynthesis, was investigated. A purified enzyme preparation from cell suspension cultures of parsley (Petroselinum hortense) catalyzed chain elongations with acetate units from malonyl-CoA, using various aromatic and aliphatic CoA esters as starter molecules. Malonyl-CoA could not be replaced by malonyl acyl carrier protein in the standard chalcone synthase assay. Butyryl-CoA, hexanoyl-CoA, and benzoyl-CoA served as substrates for the condensation reaction with similar efficiency as 4-coumaroyl-CoA, the natural substrate of the enzyme. Acetyl-CoA and octanoyl-CoA were relatively poor substrates. Among the products formed with the two most efficient aliphatic substrates tested, butyryl-CoA and hexanoyl-CoA, were the respective chalcone analogues, phlorobutyrophenone and phlorocaprophenone. The possibility is discussed that chalcone synthase and the corresponding enzyme of fatty acid synthesis in higher plants, beta-ketoacyl-acyl carrier protein synthase, have a common evolutionary origin.

Acetyl Coenzyme A↗

In vitro availability of trimethylphloroglucinol and its degradation product from dosage formulations by RP-HPLC.

A simple, sensitive, reliable, and rapid high-performance liquid chromatographic method for the simultaneous determination of phloroglucinol and trimethyl phloroglucinol has been developed. Acetonitrile-water (1:1 v/v) was used as mobile phase, with flow rate 2 ml/minutes. pH was adjusted to 3 with phosphoric acid. U.V detection was performed at 242 nm. The results obtained showed a good agreement with the declared content. Recovery values for phloroglucinol were from 99.91% to 100.62% and recovery values for trimethylphloroglucinol were from 98.44% to 100.04%. The proposed method is rapid, accurate, and selective, it may be used for the quantitative analysis of phloroglucinol and trimethylphloroglucinol. The method was found to be specific, accurate, precise and reliable for the determination of phloroglucinol and trimethylphloroglucinol in the form of raw materials, in bulk drugs and formulation. It was possible to determine both phloroglucinol and trimethylphloroglucinol in the concentration range of 5 nano gram to 30 nano grams. The detection limit of both phloroglucinol and trimethylphloroglucinol were 0.4 nano gram.

Biological Availability↗

Anti-inflammatory acylphloroglucinol derivatives from Hops (Humulus lupulus).

The polyphenol-enriched fraction of an ethanolic hops extract (Humulus lupulus) was separated to provide four acylphloroglucinol-glucopyranosides (1-4). 1-(2-Methylpropanoyl)phloroglucinol-glucopyranoside 1 has been isolated from hops before, whereas 1-(2-methylbutyryl)phloroglucinol-glucopyranoside 2, known as multifidol glucoside, and 1-(3-methylbutyryl)phloroglucinol-glucopyranoside 3 were found in hops for the first time. 5-(2-Methylpropanoyl)phloroglucinol-glucopyranoside 4 was identified as a new natural product. The compounds were tested for inhibition of COX-1 activity. The aglycon 5, obtained by acid hydrolysis of 1, was equally effective as phloroglucinol, with an IC(50) of 3.8 microM. The inhibitory potential of the glucosides was 1>2>3 and decreased with increasing length of the acyl side chain. Compound 4 was about 2.5-fold less active than 1 (IC(50): 23.7 and 58.7 microM, respectively).

Anti-Inflammatory Agents↗

Regulation of production of the antifungal metabolite 2,4-diacetylphloroglucinol in Pseudomonas fluorescens F113: genetic analysis of phlF as a transcriptional repressor.

The antifungal metabolite 2,4-diacetylphloroglucinol plays a major role in the biocontrol capabilities of Pseudomonas fluorescens. The phloroglucinol biosynthetic locus of P. fluorescens F113 has been isolated previously. From nucleotide sequence data, a putative regulator gene (phlF) was identified upstream and divergently transcribed from the phlACBD phloroglucinol biosynthetic genes. PhlF shows similarity to various transcriptional repressors in the EMBL database and exhibits a helix-turn-helix motif in its amino acid sequence. phlF was cloned into an expression vector and the PhlF protein product was purified. Gel retardation experiments demonstrated PhlF to be a DNA-binding protein and showed that it binds to the phlA-phlF intergenic region. Introduction of phlF into P. fluorescens F113 in multiple copies resulted in repression of phloroglucinol production in this strain. This effect was mediated at the transcription level since the expression of a phloroglucinol biosynthetic gene fusion in this background was equally repressed. Furthermore, the inactivation of phlF results in derepression of phloroglucinol production in this strain.

Antifungal Agents↗