UBC Theses and Dissertations
Studies on the biosynthesis of coumarins Verma, Ashok Kumar
This thesis describes the investigations on the biosynthesis of coumarins from Thamnosma montana Torr. and Frem plants and tissue cultures. Part I of this thesis discusses the degradative sequences developed for the furanocoumarins, isoimperatorin (13), allimperatorin methyl ether (7) and isopimpinellin (2) and for the coumarin, umbelliprenin (9). These degradative sequences were developed to gain information as to the distribution of radioactivity in the radioactive compounds made available from the subsequent biosynthetic studies. In Part II of this thesis, the role of mevalonate (85) in the biosynthesis of the alkyl side chains and the furan ring of furano- coumarins of Thamnosma montana tissue cultures is described. In preliminary studies, it was shown that D,L-phenylalanine-[3-¹⁴C] was being efficiently incorporated into three furanocoumarins, isoimperatorin (13), alloimperatorin methyl ether (7) and isopimpinellin (2). Incorporation experiments with various tritium labelled forms of mevalonic acid showed that mevalonic acid-[5-³H] was being incorporated into the alkyl side chain and the 6-position of the furan ring of the furanocoumarins. Similarly, experiments with mevalonic acid-[4-³H] indicated it to be a precursor of the alkyl side chains and the 7- position of the furan ring of the furanocoumarins. Mevalonic acid- [2-³H] was incorporated into the alkyl side chains but was not incorporated into the furan ring. Incorporation studies with mevalonic acid-[5-¹⁴C] supported the data already obtained with mevalonic acid- [5-³H] and revealed that any activity in the methoxy groups of furanocoumarins obtained from the [5-³H]- and [2-³H]-mevalonic acid feeding experiments was either due to a tritium exchange between the tritiated mevalonic acid and the C₁-pool in the tissue culture system or by some other unknown mechanism. Part III of this thesis describes the role of glycine (124) in the biosynthesis of the coumarins, umbelliprenin (9), alloimperatorin methyl ether (7) and isopimpinellin (2), in Thamnosma montana plants. By specific degradations, it was shown that glycine-[2-¹⁴C] was acting as an efficient precursor of the methoxyl groups of alloimperatorin methyl ether (7) and isopimpinellin (2). Glycine-[2-¹⁴C] was also shown to incorporate almost exclusively into the farnesyl-ether side chain of umbelliprenin (9) and to a small extent into the C₅-alkyl side chain of allimperatorin methyl ether (7). However, very little activity could be found in the furan ring and the coumarin portion of alloimperatorin methyl ether (7) and isopimpinellin (2). These results suggest that glycine-[2-¹⁴C] is acting as an efficient precursor of the C₁ source in Thamnosma montana plants and can also be utilized by the plant system for the biosynthesis of the C₅-alkyl side chain and, in turn, the C₁₅-alkyl-ether side chain of alloimperatorin methyl ether (7) and umbelliprenin (9), respectively.
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