Studies on the constituents of Thamnosma montana
Creators: name: Young, Robert N.
Publisher: name: University of British Columbia
Year: 2011

description: This thesis describes investigations on the natural products found in Thamnosma montana Torr. and Frem., commonly known as turpentine broom. In Part I is described the isolation and identification of fifteen constituents of Thamnosma montana. Of those compounds already known to occur in the plant, alloimperatorin methyl ether (7) and isopimpinellin (2) were found in the shoots and leaves, while β-sitosterol (6), thamnosin (8) and the alkaloids N-methylacridone (4), skimmianine (5a) and ƴ-fagarine (5b) were isolated from the roots. A number of coumarins were recognized for the first time in this plant. Umbelliprenin (83) and a new natural product, alloimperatorin methyl ether epoxide (97) were isolated from the shoots and leaves, while the coumarins, isoimpera-torin (87), phellopterin (96), psoralen (68), bergapten (67) and xantho-toxin (55) were obtained from the roots. Finally a new coumarin which we have named thamnosmin was isolated from the roots and on the basis of chemical and spectral data was assigned the structure 6-(l',2'-epoxy-3'-methyl-3-butenyl)-7-methoxycoumarin (90). Part II presents a discussion of degradative sequences developed for the furanocoumarins, isopimpinellin (2) and alloimperatorin methyl ether (7) and for the coumarin umbelliprenin (83). These sequences were developed in order to be able to gain information about the distribution of radioactivity in these compounds made available from subsequent biosynthetic studies. In Part III is described some biosynthetic experiments performed with Thamnosma montana plants. In preliminary studies it was shown that D,L-phenylalanine-[3-¹⁴C] (14) serves as an efficient precursor of the coumarin constituents in the shoots and that the rate of biosynthesis of these natural products was quite rapid. In studies on the roots, cinnamic acid-[2-¹⁴C] was shown to incorporate into the monomeric coumarin constituents but all attempts to observe positive incorporation into the dimeric coumarin thamnosin (8) were fruitless. Mevalonic acid (57) was found to be a very poor precursor of all coumarins found in Thamnosma montana shoots except in the case of umbelliprenin (83) where reasonable incorporations were observed. Mevalonic acid-[2-³H] lactone (78) was shown to incorporate essentially exclusively into the farnesyl ether side chain of umbelliprenin. Mevalonic acid-[2-³H] lactone (78) was shown not to incorporate into isopimpinellin (2) while mevalonic acid-[3R,4R-4-³H, 3S,4S-4-³H] lactone (78) did provide radioactive 2. This latter material was shown, by means of specific degradation, to have essentially all the activity at the 7-position. Sodium acetate-[2-¹⁴C] was shown to incorporate considerably more efficiently into isopimpinellin (2) and alloimperatorin methyl ether (7) than did mevalonic acid. By means of specific degradations it was shown that sodium acetate-[2-¹⁴C] provided isopimpinellin (2) labeled at C(4), C(7) and the methoxyl carbon atoms. Specific degradations revealed that the activity present in alloimperatorin methyl ether (7) was present, in part, in the C₅ side chain and the methoxyl group. These results suggest that acetate is acting both as a C-l and as a C-2 source in this plant. Possible explanations are presented.