One-pot access to l-5,6-dihalotryptophans and l-alknyltryptophans using tryptophan synthase

A Panel of TrpB Biocatalysts Derived from Tryptophan Synthase through the Transfer of Mutations that Mimic Allosteric Activation

“…Pf TrpB 0B2 has even greater difficulty with 5-bromoindole, but the Tm variant is almost six times as fast for this substrate, allowing us to obtain 5-bromotryptophan in 88% isolated yield (Table 4, entry 2). These results compare favorably with previous reports, in which TrpS from Salmonella enterica was shown to form 5-chloro and 5-bromotryptophan in 61% and 26% yield, respectively [1f] .…”

“…TrpS also reacts with myriad indole analogs, providing a direct biocatalytic route to making tryptophan derivatives. [1] In such reactions, only the β-subunit (TrpB) performs catalysis (Figure 1b), but its activity is greatly diminished in the absence of the α-subunit (TrpA), limiting its utility as a biocatalyst. [2] Recently, we applied directed evolution to the β-subunit from Pyrococcus furiosus ( Pf TrpB) to identify mutations that emulate the effect of TrpA binding and imbue the β-subunit with high activity in isolation.…”

“…This, in turn, alters properties like solubility and creates new binding interactions through effects such as π-stacking and halogen bonding. [1b, 13] Halogens can also provide handles for further diversification of biologically active compounds through cross-coupling reactions. [14] While biocatalytic routes to tryptophan derivatives tend to be inefficient and limited in substrate scope, TrpS can provide direct access to many of these products.…”

“…[14] While biocatalytic routes to tryptophan derivatives tend to be inefficient and limited in substrate scope, TrpS can provide direct access to many of these products. Previously, however, 5-substituted indoles bearing anything larger than fluorine caused a substantial decrease in activity [1d, 1f, 15] . Furthermore, TrpS activity with electron-deficient indoles had not been explored.…”

Hot off the press

“…A recent issue of Tetrahedron (2016, 72, issue 46) has been dedicated to "modern developments in biotransformations" and contain a range of articles on biocatalyst development, including the one-pot preparation of L-dihalotryptophans and Lalkynyltryptophans (Scheme 4) from L-serine and indoles using tryptophan synthase. 27 Extensive protein engineering of the transaminase from Ruegeria sp.…”