Biotransformation of selected natural products and phytochemistry of fermented Alnus sieboldiana and liverwort Conocephalum conicum / Nurunajah Ab Ghani
Biotransformation is a process by which organic compounds are transformed into its derivatives, aided by organisms such as fungi, bacteria and enzymes. Biotransformations are used as a valuable strategy to diversify chemistry of compounds particularly natural products. The aim of this work is to explore biotransformation on natural products using several concepts, in order to obtain varieties of natural entities. This thesis presents biotransformation studies on two classes of bioactive natural products represented by an anthraquinone and chalcones, followed by in-situ transformation of chemical constituents of male flowers by fungus, and changes in biosynthetic pathways when Japanese liverwort is grown under stressed condition. Small scale biotransformation of the bioactive anthraquinone nordamnacanthal 8 using 19 selected strains revealed its sturdy nature where only Absidia coerulea managed to convert the compound into lucidin 143. Then, in-labo biotransformation was pursued with microbial transformation of hydroxychalcones; 4'- hydroxychalcone 145 and 4-hydroxychalcone 146 by Aspergillus niger. After 7 days of fermentation, four dihydrochalcone derivatives were obtained. Isolated products were identified as 4'-hydroxydihydrochalcone 147, 4-hydroxydihydrochalcone 149, 3\4'-dihydroxydihydrochalcone 148 and 3,4-dihydroxydihydrochalcone 150, resulting from bioreduction at a,P-unsaturated double bond of hydroxychalcone and hydrogenation reaction at the activated phenyl rings. On the other hand, in-situ transformation of Alnus sieboldiana male flowers by fungus Penicillium sp. is of interest due to the common infection causing significant change in the smell. Infected male flowers were allowed to ferment for six months. Analysis of the volatile components of the fermented male flowers revealed P-phenylethyl cinnamate 174 (10%) as a major component followed by 2-phenylethanol 170 (8.7%). The level of 2- phenylethanol 170 in the fermented male flowers is three times higher as compared to the fresh male flowers (2.7%) which explained the unpleasant odor of fermented male flowers. Yashabushidiol A 72, yashabushidiol B 73 and naringenin 69, which were known to be original constituents of the fresh male flowers, were successfully isolated from the ethyl acetate extract of fermented male flowers. Additional transformation products isolated includes six flavonoids kaempferol 195, quercetin 196, pinocembrin dimethyl ether 197, /Lram-3-hydroxy-5,7-dimethoxyflavanone 198, galangin-5,7- dimethyl ether 199 and 5-methoxy-3,6,7-trihydroxyflavanone 200. Detailed analysis of the metabolic pathways of isolated compounds suggested flavanone-3-hydroxylase, flavonoid-3'-hydroxylase and plant-O-methyl-transferases enzymes were released due to the enzymatic action of fungus Penicillium sp. When Japanese liverwort Conocephalum conicum was grown under stressed condition, the biosynthesis pathways taking place in the plant seem to be affected resulting in confusions from chemotype perspective. Under normal growth conditions, (+)-bornyl acetate 94 is the major component in the type-II C. conicum while ds-methyl cinnamate 204 and transmethyl cinnamate 87 should not be present. However, when grown under stressed conditions, ^nms-methyl cinnamate 87 was found to be present as the major component instead of (+)-bornyl acetate 94, indicating activation of shikimate pathway along with mevalonic acid pathway. Thus, it is suggested that the stress C conicum to be categorized under Vnms-methyl cinnamate > bornyl acetate' subtype, since there were dual biogenetic pathways present at stressed condition
