UC Berkeley

The following Dissertation discusses the use of transition metals to enable the installation and modification of benzylic difluoromethylene units and the use of homogenous, heterogenous, and chemo-enzymatic catalysts to enable the selective functionalization of olefins.Chapter 1 reviews recent applications of biocatalysis in the pharmaceutical industry during the period 2020–2025. The application of biocatalysis to industrial chemistry has been a longstanding challenge, and has been historically limited due to the small amounts of enzyme that were typically available. Over the last 70 years, major advances in technology in the fields of proteomics, enzyme engineering, chemical biology, and process engineering have reduced the barrier to entry for the use of biocatalysis. These technological improvements have enabled the efficient and sustainable synthesis biocatalysts that are capable of transformations relevant to the synthesis of active pharmaceutical ingredients, key intermediates, and valuable chemical building blocks under mild, often aqueous conditions and with minimal environmental impact. Case studies; including the synthesis of Esomeprazole, Nemtabrutinib, Belzutifan, Molnupiravir, and Uvelostinag; illustrate the transformation of traditional chemical manufacturing routes into processes that integrate biocatalytic transformations. These examples, and others, highlight the successful application of enzymes to the synthesis of biologically-active compounds in the pharmaceutical industry. Key to the success of biocatalytic methods is the strategic use of enzyme engineering to enhance activity and selectivity, and the development of robust multi-enzyme cascades that streamline manufacturing while reducing waste and energy demand.Chapter 2 describes the development of a sequential chemoenzymatic method to form linear, primary amines from olefins. Methods that form amines from feedstock chemicals are an important component of industrial chemistry. Many methods for the synthesis of amines yield mixtures of primary, secondary, and tertiary amines, necessitating costly downstream separations. We present a chemoenzymatic approach to hydroaminomethylation that addresses these challenges by combining hydroformylation catalyzed by a phosphine-bound rhodium complex with enzymatic transamination catalyzed by an ω-transaminase from Vibrio fluvialis (VfTA). This sequential chemoenzymatic hydroaminomethylation reaction converts olefins to linear primary amines with high regioselectivity and chemoselectivity for the linear primary amine, and we demonstrate that this process occurs with a series of olefins with varying structures. Furthermore, we report progress toward a tandem process that incorporates a biocatalytic cascade for recycling an intermediate amine donor, which is required for the transaminase enzyme to use an ammonium salt as the terminal nitrogen source. This study illustrates the potential to combine chemo- and biocatalytic reactions to produce valuable materials from readily available feedstocks in both tandem and sequential processes, with selectivities that have not been achieved with transition-metal catalysts.Chapter 3 describes the development of a tandem chemoenzymatic method to achieve the synthesis of linear, primary amines from olefins using feedstock reagents and mild conditions. Linear primary amines serve as crucial building blocks in pharmaceuticals, fine chemicals, polymers, and surfactants. Despite their importance, conventional methods for the synthesis of linear primary amines often suffer from overalkylation and the requirement for elevated temperatures and pressures. Herein, we report a tandem chemoenzymatic hydroaminomethylation strategy that converts terminal olefins into linear primary amines under mild conditions by integrating a Rh/DPPon‐catalyzed hydroformylation performed in surfactant micelles with a wild‐type ω‐ transaminase from wild-type Vibrio fluvialis (WT-VfTA) and an amine donor recycling system composed of wild‐type alanine dehydrogenase (WT-AlaDH) and wild-type glucose dehydrogenase (WT-GDH) enzymes. This cooperative cascade uses inexpensive feedstock reagents—including ammonium salts, alanine, carbon monoxide, hydrogen, and glucose—to achieve high selectivity for primary amines without the formation of secondary and tertiary amine byproducts. Moreover, the system’s versatility is demonstrated by the synthesis of 15N‐labeled primary amines and biologically relevant compounds containing linear primary amines, underscoring the potential of this integrated tandem process and other chemoenzymatic methods for applications ranging from medicinal chemistry to industrial manufacturing.Chapter 4 describes the development of a copper-mediate C–C bond-forming reaction that installs a cyanodifluoromethyl group in the place of (hetero)aryl iodides and bromides. The cyanodifluoromethyl group is unique because its size is closer than that of any other substituted difluoromethyl group to the size of the trifluoromethyl group, but its electronic properties are distinct from those of the trifluoromethyl group. In addition, the presence of the cyano group provides synthetic entry to a wide range of substituted difluoromethyl groups. However, the synthesis of cyanodifluoromethyl compounds requires multiple steps, highly reactive reagents (such as DAST, NSFI, or IF5), or specialized starting materials (such as α,α-dichloroacetonitriles or α-mercaptoacetonitriles). Herein, we report a copper-mediated cyanodifluoromethylation of aryl and heteroaryl iodides and activated aryl and heteroaryl bromides with TMSCF2CN. This cyanodifluoromethylation tolerates an array of functional groups, is applicable to late-stage functionalization of complex molecules, yields analogues of FDA-approved pharmaceuticals and fine chemicals, and enables the synthesis of a range of complex molecules bearing a difluoromethylene unit by transformations of the electron-poor CN unit. Calculations of selected steps of the reaction mechanism by Density Functional Theory indicate that the barriers for both the oxidative addition of iodobenzene to [(DMF)CuCF2CN] and the reductive elimination of the fluoroalkyl product from the fluoroalkyl copper intermediate lie in between those of [(DMF)CuCF3] and [(DMF)CuCF2C(O)NMe2].Chapter 5 describes the development of a palladium-catalyzed desymmetrization reaction of benzylic difluoromethylene units. Molecules containing fluorine are widespread in modern materials, agrochemicals, and pharmaceuticals because the inclusion of fluorine in a molecule can beneficially modulate the physiochemical properties of the parent molecule. Stereocenters bearing fluorine are particularly valuable as bio-isosteres of alcohols and of C(sp3)-H bonds. Preparing different isomers of secondary and tertiary benzylic fluorides can affect molecular conformation and modulate biological activity; however, synthesizing these chiral alkyl fluorides from nonchiral starting materials is challenging. We report a palladium-catalyzed desymmetrization strategy for the alkylation of (hetero)aryl-α,α-difluoromethylene units that enables the synthesis of enantioenriched 2° and 3° C(sp3) stereocenters bearing fluorine. The use of Ba(OTf)2 as Lewis acid, LiOtBu as base, and the novel germanium-containing bisphosphine ligand (R)-DTMGMBINAP (DTMGM = 3,5-(trimethylgermanyl)-4-methoxyphenyl), enables the desymmetrization of (hetero)aryl-α,α-difluorides in high yields and in high enantioselectivities under mild conditions. We demonstrate that a wide range of carbon nucleophiles and a wide range of benzylic difluorides react under the developed conditions. Additionally, the use of a masked acyl cyanide nucleophile enables rapid functionalization of the fluorinated products to form stereo-defined α-fluorinated carbonyl compounds.