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Here, we report a novel diastereo- and enantioselective photobiocatalytic three-component radical coupling unknown in both organic chemistry and enzymology, enabled by cooperative catalysis employing an evolved pyridoxal biocatalyst and a transition-metal photosensitizer. Directed evolution using high-throughput photobiocatalysis furnished two threonine aldolase variants, enabling the stereoselective assembly of contiguous tri- and tetrasubstituted stereocenters as well as vicinal tetrasubstituted stereocenters, which were long regarded as a challenging goal for stereoselective radical chemistry and asymmetric catalysis. Furthermore, a variety of radical precursors, including \u03b1-iodoesters, \u03b1-iodoamides, \u03b1-iodoketones, and \u03b1-iodonitriles, could be transformed into structurally diverse, densely substituted non-canonical amino acid derivatives via C\u2013H functionalization with excellent stereocontrol. Leveraging the broad substrate compatibility of engineered pyridoxal biocatalysts, combinatorial biocatalysis was achieved by simultaneously varying all three coupling partners, delivering products with a 98% success rate. Collectively, this diversity-generating multicomponent photobiocatalytic radical coupling afforded a powerful strategy for addressing long-standing challenges in asymmetric catalysis while enabling access to valuable stereochemically complex small molecules with applications in medicinal chemistry.<\/jats:p>","DOI":"10.64898\/2026.09.25.754468","type":"posted-content","created":{"date-parts":[[2026,9,28]],"date-time":"2026-09-28T10:45:13Z","timestamp":1790592313000},"source":"Crossref","is-referenced-by-count":0,"title":["Asymmetric assembly of congested contiguous stereocenters via photobiocatalytic three-component radical coupling"],"prefix":"10.64898","author":[{"ORCID":"https:\/\/orcid.org\/0000-0002-1750-0058","authenticated-orcid":false,"given":"Qingdong","family":"Hu","sequence":"first","affiliation":[{"name":"Department of Chemistry and Biochemistry, University of California, Santa Barbara, California 93106, USA"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Cang-Xin","family":"Zheng","sequence":"additional","affiliation":[{"name":"Department of Chemistry and Biochemistry, University of California, Santa Barbara, California 93106, USA"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"ORCID":"https:\/\/orcid.org\/0000-0001-8487-1417","authenticated-orcid":false,"given":"Binh Khanh","family":"Mai","sequence":"additional","affiliation":[{"name":"Department of Chemistry, University of Pittsburgh, Pittsburgh, Pennsylvania 15260, USA"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"ORCID":"https:\/\/orcid.org\/0000-0002-8188-632X","authenticated-orcid":false,"given":"Peng","family":"Liu","sequence":"additional","affiliation":[{"name":"Department of Chemistry, University of Pittsburgh, Pittsburgh, Pennsylvania 15260, USA"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"ORCID":"https:\/\/orcid.org\/0000-0002-4956-2034","authenticated-orcid":false,"given":"Yang","family":"Yang","sequence":"additional","affiliation":[{"name":"Department of Chemistry and Biochemistry, University of California, Santa Barbara, California 93106, USA"},{"name":"Department of Bioengineering, University of California, Santa Barbara, California 93106, USA"},{"name":"Biomolecular Science and Engineering (BMSE) Program, University of California, Santa Barbara, California 93106, USA"},{"name":"Howard Hughes Medical Institute, University of California, Santa Barbara, California 93106, USA"}],"role":[{"vocabulary":"crossref","role":"author"}]}],"member":"54368","reference":[{"key":"2026093008501400000_2026.09.25.754468v1.1","doi-asserted-by":"crossref","first-page":"5459","DOI":"10.1021\/acs.chemrev.2c00767","volume":"123","year":"2023","journal-title":"Chem. 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