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Spiro-oxindole scaffolds have been studied due to their promising therapeutic potential. In the Amazon rainforest there are two important  Uncaria  species known as “cat’s claw”, which biosynthesize spirocyclic oxindole alkaloids;  Uncaria tomentosa  (Willd. ex Schult.) DC. and  Uncaria guianensis  (Aublet) Gmell. We carried out a precursor-directed biosynthesis approach with  U. guianensis  and successfully obtained oxindole alkaloid analogues with molecular mass corresponding to the addition of a methyl or fluorine group on the oxindole ring using tryptamine analogue precursors. Two of these novel oxindole alkaloid analogues ( 3b -7-methyl-isomitraphylline and  3c -6-fluoro-isomitraphylline) were isolated and characterized by NMR spectroscopy and ESI-QTOF-MS/MS. Having established a substrate feeding protocol for these plantlets, the biosynthetic route for mitraphylline ( 1 ), rhynchophylline ( 2 ), isomitraphylline ( 3 ) and isorhynchophylline ( 4 ) was also investigated using  13 C-precursors (1- 13 C-D-glucose, 2- 13 C-tryptophan, 1- 13 C-DL-glyceraldehyde, and methyl- 13 C-D-methionine).

Unnatural spirocyclic oxindole alkaloids biosynthesis in Uncaria guianensis