Antimetabolites are small molecules that inhibit enzymes by mimicking physiological substrates. We report the discovery and structural elucidation of the antimetabolite 7-deoxy-sedoheptulose (7dSh). This unusual sugar inhibits the growth of various prototrophic organisms, including species of cyanobacteria, Saccharomyces, and Arabidopsis. We isolate bioactive 7dSh from culture supernatants of the cyanobacterium Synechococcus elongatus. A chemoenzymatic synthesis of 7dSh using S. elongatus transketolase as catalyst and 5-deoxy-d-ribose as substrate allows antimicrobial and herbicidal bioprofiling. Organisms treated with 7dSh accumulate 3-deoxy-d-arabino-heptulosonate 7-phosphate, which indicates that the molecular target is 3-dehydroquinate synthase, a key enzyme of the shikimate pathway, which is absent in humans and animals. The herbicidal activity of 7dSh is in the low micromolar range. No cytotoxic effects on mammalian cells have been observed. We propose that the in vivo inhibition of the shikimate pathway makes 7dSh a natural antimicrobial and herbicidal agent.

Edited by Chris Whitfield 5-Deoxyadenosine (5dAdo) is the byproduct of many radical S-adenosyl-L-methionine enzyme reactions in all domains of life. 5dAdo is also an inhibitor of the radical S-adenosyl-Lmethionine enzymes themselves, making it necessary for cells to construct pathways to recycle or dispose of this toxic metabolite. However, the specific pathways involved have long remained unexplored. Recent research demonstrated a growth advantage in certain organisms by using 5dAdo or intermediates as a sole carbon source and elucidated the corresponding salvage pathway. We now provide evidence using supernatant analysis by GC-MS for another 5dAdo recycling route. Specifically, in the unicellular cyanobacterium Synechococcus elongatus PCC 7942 (S. elongatus), the activity of promiscuous enzymes leads to the synthesis and excretion first of 5-deoxyribose and subsequently of 7-deoxysedoheptulose. 7-Deoxysedoheptulose is an unusual deoxy-sugar, which acts as an antimetabolite of the shikimate pathway, thereby exhibiting antimicrobial and herbicidal activity. This strategy enables organisms with small genomes and lacking canonical gene clusters for the synthesis of secondary metabolites, like S. elongatus, to produce antimicrobial compounds from primary metabolism and enzymatic promiscuity. Our findings challenge the view of bioactive molecules as sole products of secondary metabolite gene clusters and expand the range of compounds that microorganisms can deploy to compete for their ecological niche.

The design of distinctive chemical synthesis strategies aims for the most efficient routes towards versatile compounds in drug target studies. Here, we establish a powerful hybrid synthetic approach of total chemical and chemoenzymatic synthesis to efficiently obtain various 7-deoxy-sedoheptulose (7dSh, 1) analogues, unique C 7 sugars, for structure-activity relationship studies. 7dSh (1) is a rare microbial sugar with in planta herbicidal activity. As natural antimetabolite of 3-dehydroquinate synthase (DHQS), 7dSh (1) inhibits the shikimate pathway, which is essential for the synthesis of aromatic amino acids in bacteria, fungi, and plants, but absent in mammals. As glyphosate, the most used chemical herbicide faces restrictions worldwide, DHQS has gained more attention as valid target of herbicides and antimicrobial agents. In vitro and in vivo analyses of the C 7 -deoxysugars confirm DHQS as enzymatic target, highlight the crucial role of uptake for inhibition and add molecular aspects to target mechanism studies of C 7 -sugars as our contribution to global efforts for alternative weed-control strategies.

Abstract7-Deoxysedoheptulose is an unusual deoxy-sugar, which acts as antimetabolite of the shikimate pathway thereby exhibiting antimicrobial and herbicidal activity. It is produced by the unicellular cyanobacterium Synechococcus elongatus PCC 7942, which has a small, stream-lined genome, assumed to be free from gene clusters for secondary metabolite synthesis. In this study, we identified the pathway for the synthesis of 7-deoxysedoheptulose. It originates from 5-deoxyadenosine, a toxic byproduct of radical S-adenosylmethionine (SAM) enzymes, present in all domains of life. Thereby we identified a novel 5-deoxyadenosine salvage pathway, which first leads to the synthesis and excretion of 5-deoxyribose and subsequently of 7-deoxysedoheptulose. Remarkably, all reaction steps are conducted by promiscuous enzymes. This is a unique example for the synthesis of a bioactive compound without involving a specific gene cluster. This challenges the view on bioactive molecule synthesis by extending the range of possible compounds beyond the options predicted from secondary metabolite gene clusters.