The electrochemical cathodic reduction of cyclic imides (maleimides) to succinimides can be achieved chemoselectively in the presence of alkene, alkyne, and benzyl groups. The efficiency of the system was demonstrated by using a 3D electrode in a continuous flow reactor. The reduction of 3,4‐dimethylmaleimides to the corresponding succinimides proceeds with a 3:2 diastereomeric ratio, which is independent of the nitrogen substituent and electrode surface area. The stereoselectivity of the process was rationalized by using DFT calculations, involving an acid‐catalyzed tautomerization of a half‐enol occurring through a double hydrogen‐transfer mechanism.

The elucidation of enigmatic enzymatic chlorination timing in ambiguine indole alkaloid biogenesis led to the discovery and characterization of AmbO5 protein as a promiscuous non-heme iron aliphatic halogenase. AmbO5 was shown capable of selectively modifying seven structurally distinct ambiguine, fischerindole and hapalindole alkaloids with chlorine via late-stage aliphatic C-H group functionalization. Cross-comparison of AmbO5 with a previously characterized aliphatic halogenase homolog WelO5 that has a restricted substrate scope led to the identification of a C-terminal sequence motif important for substrate tolerance and specificity. Mutagenesis of 18 residues of WelO5 within the identified sequence motif led to a functional mutant with an expanded substrate scope identical to AmbO5, but an altered substrate specificity from the wild-type enzymes. These observations collectively provide evidence on the evolvable nature of AmbO5/WelO5 enzyme duo in the context of hapalindole-type alkaloid biogenesis and implicate their promise for the future development of designer biocatalysis for the selective late-stage modification of unactivated aliphatic carbon centers in small molecules with halogens.

In vitro reconstitution of a newly discovered isonitrile synthase (AmbI1 and AmbI2) and the detection of an elusive intermediate (S)-3-(1H-indol-3-yl)-2-isocyanopropanoic acid 1 in indolyl vinyl isocyanide biogenesis are reported. The characterization of iron/2-oxoglutarate (Fe/2OG) dependent desaturases IsnB and AmbI3 sheds light on the possible mechanism underlying stereoselective alkene installation to complete the biosynthesis of (E)- and (Z)-3-(2-isocyanovinyl)-1H-indole 2 and 5. Establishment of a tractable isonitrile synthase system (AmbI1 and AmbI2) paves the way to elucidate the enigmatic enzyme mechanism for isocyanide formation.

Promiscuous cis-indolyl vinyl isonitrile biosynthetic pathway allowed the preparatively useful generation of nine halosubstituted antibiotic analogues with increased lipophilicity.

…A mbO5 was identified in studies of ambiguine alkaloid biogenesis.I nt heir Communication on page 5780 ff., X. Liu et al. show that AmbO5 can selectively chlorinate seven structurally distinct ambiguine,fischerindole,and hapalindole alkaloids by late-stage CÀHf unctionalization. Thec haracterization of aC -terminal sequence motif in AmbO5 important for substrate tolerance and specificity provides evidence on the evolvable nature of this newly discovered halogenase family towards small molecules.