Department of Chemistry, University of Kentucky, Lexington, Kentucky, 40546-0312, USA.
Department of Chemistry, The Pennsylvania State University, University Park, Pennsylvania, 16802, USA.
Chembiochem. 2022 Jul 5;23(13):e202200081. doi: 10.1002/cbic.202200081. Epub 2022 May 17.
LolO, a 2-oxoglutarate-dependent nonheme Fe oxygenase, catalyzes both the hydroxylation of 1-exo-acetamidopyrrolizidine (AcAP), a pathway intermediate in the biosynthesis of the loline alkaloids, and the cycloetherification of the resulting alcohol. We have prepared fluorinated AcAP analogues to aid in continued mechanistic investigation of the remarkable LolO-catalyzed cycloetherification step. LolO was able to hydroxylate 6,6-difluoro-AcAP (prepared from N,O-protected 4-oxoproline) and then cycloetherify the resulting alcohol, forming a difluorinated analogue of N-acetylnorloline and providing evidence for a cycloetherification mechanism involving a C(7) radical as opposed to a C(7) carbocation. By contrast, LolO was able to hydroxylate 7,7-difluoro-AcAP (prepared from 3-oxoproline) but failed to cycloetherify it, forming (1R,2R,8S)-7,7-difluoro-2-hydroxy-AcAP as the sole product. The divergent LolO-catalyzed reactions of the difluorinated AcAP analogues provide insight into the LolO cycloetherification mechanism and indicate that the 7,7-difluorinated compound, in particular, may be a useful tool to accumulate and characterize the iron intermediate that initiates the cycloetherification reaction.
LolO 是一种依赖 2-氧代戊二酸的非血红素 Fe 加氧酶，能够催化 1-外消旋-乙酰氨基吡咯里西啶（AcAP）的羟化以及所得醇的环醚化，AcAP 是洛洛碱生物合成途径中的中间产物。我们已经制备了氟化的 AcAP 类似物，以帮助进一步研究 LolO 催化的环醚化反应的显著机制。LolO 能够羟化 6,6-二氟-AcAP（由 N,O-保护的 4-氧代脯氨酸制备），然后环醚化所得醇，形成 N-乙酰降洛林的二氟类似物，并提供涉及 C(7)自由基而不是 C(7)碳正离子的环醚化机制的证据。相比之下，LolO 能够羟化 7,7-二氟-AcAP（由 3-氧代脯氨酸制备），但不能环醚化它，形成（1R,2R,8S）-7,7-二氟-2-羟基-AcAP 作为唯一产物。二氟代 AcAP 类似物的不同 LolO 催化反应提供了对 LolO 环醚化机制的深入了解，并表明特别是 7,7-二氟代化合物可能是一种有用的工具，可以积累和表征引发环醚化反应的铁中间物。
