By A. Douglas Kinghorn, Heinz Falk, Simon Gibbons, Jun'ichi Kobayashi
The first contribution studies the incidence of xanthine alkaloids within the plant country and the elucidation of the caffeine biosynthesis pathway, offering info of the N-methyltransferases, belonging to the motif B' methyltransferase relatives which catalyze 3 steps within the 4 step pathway prime from xanthosine to caffeine. the second one contribution during this ebook presents a heritage at the molecule and similar compounds and replace wisdom at the latest advances in Iboga alkaloids. The 3rd contribution provides a entire research of usually taking place mistakes with appreciate to 13C NMR spectroscopic facts and proposes an easy protocol to put off a excessive percent of the obvious errors.
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Additional resources for Progress in the Chemistry of Organic Natural Products 105
However, current data from a series of studies on in situ metabolism of labeled precursors and characterization of enzymes and genes have established that the main caffeine (8) biosynthesis pathway is a four-step sequence consisting of three methylations and one nucleosidase reaction starting with xanthosine (16) serving as the initial substrate. The conversion of 16 to 8 involves three N-methylation steps (steps 1, 3, and 4 in Fig. 6) and the removal of a ribose moiety (step 2 in Fig. 6). The main pathway is via theobromine (5).
These observations strongly suggest that 8 accumulated in coffee seeds is mainly synthesized in the seeds. This contradicts an early paper in which Baumann and Wanner  argued that in Coffea arabica fruits 8 in the seeds was derived from the pericarp. Theobroma The biosynthetic activity of theobromine (5) has been investigated in the leaves and fruits of Theobroma cacao [56, 61]. Koyama et al.  examined purine metabolism in young small leaves, developing, intermediate-sized leaves, and fully developed leaves from flush shoots of cacao trees, and aged leaves from 1-year-old shoots.
Conversion to 24 was enhanced at higher concentrations of 17 in the Table 7 Substrate specificity and products of native and recombinant 7-methylxanthosine synthase from coffee plantsa Sample C. arabica (native, crude) Substrate Xanthosine (16) XMP (17) C. arabica (recombinant) C. arabica (recombinant) C. canephora (recombinant) Xanthosine (16) XMP (17) Xanthosine (16) XMP (17) Xanthosine (16) XMP (17) Product(s) 7mXR (23) 7mX (2) 7mXMP (24) 7mXR(23) 7mX (2) 7mXR (23) None 7mXR (23) None 7mX (2) None 7mX ¼ 7-methylxanthine (2), 7mXR ¼ 7-methylxanthosine (23) a Relative rate/% 29 71 18 57 23 100 – 100 – 100 – Ref.