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Simple densitometric TLC analysis of plaunotol for screening of high-plaunotol-containing plants of Croton stellatopilosus Ohba
(2009-02-01)
Rinthong, Prasob Orn
;
Jindaprasert, Aphacha
;
De-Eknamkul, Wanchai
Plaunotol, an anti-peptic diterpenoid present in the leaves of Croton stellatopilosus Ohba, was separated from other components of crude methanolic extracts and quantified by densitometric TLC. Validation of precision, repeatability, and accuracy showed the technique was reliable, with 98.7% recovery of externally added plaunotol. Crude extracts of different leaf samples could be applied directly to silica gel TLC plates without prior sample preparation or concentration of the extracts. Plates were chromatographed with chloroform-n-propanol 96:4 (v/v) as mobile phase then scanned at 220 nm. The results showed that the plaunotol content of the leaves of C. stellatopilosus was highly variable (range 0.14 to 0.79% w/w of dry weight). Although most (35%) leaf samples seemed to contain 0.3-0.4% plaunotol, 8% contained more than 0.6%. This densitometric TLC method could, therefore, be a useful tool for screening of high-plaunotol-producing C. stellatopilosus plants as effective sources of the compound. © 2009 Akadémiai Kiadó.
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Pyrone polyketides synthesized by a type III polyketide synthase from Drosophyllum lusitanicum
(2008-12-01)
Jindaprasert, Aphacha
;
Springob, Karin
;
Schmidt, Jürgen
;
De-Eknamkul, Wanchai
;
Kutchan, Toni M.
To isolate cDNAs involved in the biosynthesis of acetate-derived naphthoquinones in Drosophyllum lusitanicum, an expressed sequence tag analysis was performed. RNA from callus cultures was used to create a cDNA library from which 2004 expressed sequence tags were generated. One cDNA with similarity to known type III polyketide synthases was isolated as full-length sequence and termed DluHKS. The translated polypeptide sequence of DluHKS showed 51-67% identity with other plant type III PKSs. Recombinant DluHKS expressed in Escherichia coli accepted acetyl-coenzyme A (CoA) as starter and carried out sequential decarboxylative condensations with malonyl-CoA yielding α-pyrones from three to six acetate units. However, naphthalenes, the expected products, were not isolated. Since the main compound produced by DluHKS is a hexaketide α-pyrone, and the naphthoquinones in D. lusitanicum are composed of six acetate units, we propose that the enzyme provides the backbone of these secondary metabolites. An involvement of accessory proteins in this biosynthetic pathway is discussed. © 2008 Elsevier Ltd. All rights reserved.
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Rapid TLC-densitometric analysis of plaunotol from Croton sublyratus leaves
(1998-01-01)
Vongchareonsathit, Aphacha
;
De-Eknamkul, Wanchai
A simple, rapid, and accurate method of TLC-densitometry was developed to quantitate plaunotol, an antipeptic ulcer diterpenoid, in the leaves of Croton sublyratus Kurz (Euphorbiaceae). Plaunotol was extracted with boiling 95% ethanol and the unpurified extracts were used directly for the analysis of plaunotol by the TLC-densitometric method. TLC was carried out using silica gel and the solvent system of chloroform: n-propanol, 96:4. Densitometric scanning of the TLC plate was performed using the wavelength of 220 nm. The developed technique showed high accuracy and precision as compared with the GC method and could detect plaunotol at a quantity of as low as 0.12 μg. Preliminary experiments indicate that the technique can be a useful tool in the screening of Croton sublyratus plants containing high plaunotol content.

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