Aza-tryptamine substrates in monoterpene indole alkaloid biosynthesis

Abstract

Biosynthetic pathways can be hijacked to yield novel compounds by introduction of novel starting materials. Here we have altered tryptamine, which serves as the starting substrate for a variety of alkaloid biosynthetic pathways, by replacing the indole with one of four aza-indole isomers. We show that two aza-tryptamine substrates can be successfully incorporated into the products of the monoterpene indole alkaloid pathway in Catharanthus roseus. Use of unnatural heterocycles in precursor-directed biosynthesis, in both microbial and plant natural product pathways, has not been widely demonstrated, and successful incorporation of starting substrate analogs containing the aza-indole functionality has not been previously reported. This work serves as a starting point to explore fermentation of aza-alkaloids from other tryptophan- and tryptamine-derived natural product pathways.

Figure 1

The aza-indole moiety (highlighted in red) in natural and synthetic compounds. A. Aza-indoles in natural products. B. Aza-indole moiety in an indole natural product analog. C. Synthetic pharmaceutically important compounds containing an aza-indole group.

Figure 2

Synthesis of aza-tryptamine compounds 1–4.

Figure 3

Figure 3A. Reaction of aza-tryptamine compounds 1–4 in a Pictet-Spengler reaction. B. Formation of downstream alkaloid and aza-alkaloid products.

Figure 4

LC-MS spectra showing production of new compounds by Catharanthus roseus when supplemented with deglycosylated strictosidine derived from 1 and 4. Starred peaks indicate compounds found only in cultures supplemented with deglycosylated strictosidine derived from 1 or 4. LC-MS spectra showing the results of feeding deglycosylated strictosidine 11 derived from natural tryptamine 5 to cell cultures are shown in the Supporting Information.