Questions

1. Note that reserpine (Figure 9.1) has a mixed biosynthetic origin. The centre part is more difficult, but what are the precursors of the left-and right-hand parts?

2. Note that both portions of the molecule of exochomine (Figure 9.9) have 13 carbon atoms. Suggest a biosynthetic scheme for the formation of the dimethylaza-acenaphthalenone portion.

3. The biosynthesis of solenopsin (cis and trans) was studied by feeding sodium [l-14C]acetate (activity 60 mCi mmol"1) to several thousand ants of S. geminata over 60 h. The solenopsins were then isolated and found to contain 6.1 x 10~3 mCi mmol-1. Calculate the % incorporation of acetate into solenopsins.

4. (a) In the experiment above with sodium [l-14C]acetate, the methyl group on the pyrimidine ring of the solenopsins was selectively removed (for details of the method, see Leclercq, Braekman, Daloze, Pasteels and Vander Meer, Naturwissenschaften, 1996, 83, 222). What fraction of the total radioactivity would be expected in this carbon atom?

(b) In a repeat of the experiment with [2-14C]acetate, used in exactly the same way, how much of the radioactivity would be expected in this same carbon atom?

5. The pupae of the ladybird Subcoccinella vigintiquatuorpunctata are protected by hairs which contain oily droplets. HPLC-mass spectrometry showed the secretion consisted mainly of three compounds that have molecular masses of 530, 532, and 534. They are derived from the compounds below (compare Figure 3.29). Suggest molecular structures for the three compounds. The three compounds all contain free NH groups but are not acidic.

mol. mass 283 mol. mass 285

mol. mass 283 mol. mass 285

In a study of luciferin biosynthesis in the beetle Pyrearinus termitil-luminans uniformly labelled cysteine (14C(U)cysteine, 30 nCi per insect) was injected into five insects and after two days the luciferin was separated by thin layer chromatography and counted. In the total extract of five insects, 480 dps were found. What is the specific incorporation of cysteine into luciferin?

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