In Situ Enzymatic Screening (ISES): A Tool for Catalyst Discovery and Reaction Development

Abstract

Can enzymes help organic chemists identify new transition‐metal catalysts? The first example of the in situ enzymatic monitoring of an organic transformation is described. Thus, a transition‐metal‐mediated allylic‐amination reaction in the organic layer (see scheme; R=para‐methoxyphenyl, tosyl) leads to release of ethanol which causes the spectroscopically observable formation of NADH in the aqueous phase. This approach uncovers a new Ni0‐promoted route to β,γ‐unsaturated amino acids. HMDS=1,1,1,3,3,3‐hexamethyldisilazane.

Exploiting Enzymatic Dynamic Reductive Kinetic Resolution (DYRKR) in Stereocontrolled Synthesis

“…[12] Our own interest in dehydrogenase enzymes stems from their utility as “reporting enzymes” in a method for catalyst discovery that we have developed known as In Situ Enzymatic Screening (ISES). [13] In this approach, an alcohol dehydrogenase (ADH) oxidizes the alcoholic product or byproduct of a reaction of interest. The concomitant increase in Abs 340 associated with the formation of NAD(P)H is monitored spectroscopically.…”

A new dehydrogenase from Clostridium acetobutylicum for asymmetric synthesis: dynamic reductive kinetic resolution entry into the Taxotère side chain

“…8,9 Of late, that focus has been especially on alcohol dehydrogenases (ADHs), both for asymmetric carbonyl reduction 10 and for installation of a center alpha- to a carbonyl, via dynamic reductive kinetic resolution (DYRKR), using a hyperthermophilic archael dehydrogenase. 11 …”

The In Situ Enzymatic Screening (ISES) Approach to Reaction Discovery and Catalyst Identification

“…For example, the product must diffuse into the aqueous reporting phase readily enough to obtain useful initial rate information. Adjusting the solvent composition may facilitate product diffusion and can also limit the rate of water diffusion into the organic layer (Berkowitz et al, 2002). Proper solvent choice also limits precipitation at the organic/aqueous interface, a significant issue when an upper organic layer is used.…”

“…The first iteration of ISES was developed to explore catalytic combinations for a transition metal-mediated intramolecular amination (Berkowitz et al, 2002; Berkowitz and Maiti, 2004; Berkowitz et al, 2004) reaction upon an allylic ethyl carbonate substrate (Figure 1, Basic Protocol 1). Turnover of such substrates is expected to proceed via formation of a π-allyl or σ-allyl-metal intermediate with release of the ethyl carbonate leaving group in each catalytic cycle.…”

“…This is an example of the use of ISES for air-sensitive chemistry, as can be seen in Figure 1B, the cuvettes have all been purged with Ar, and are held under inert atmosphere via septa. Indeed, ISES was used to identify the combination of p-methoxyphenyl (PMP) protection on the nucleophilic nitrogen, Ni(cod) 2 and bidentate phosphine ligands were found to be optimal based solely on iterative ISES screening (Berkowitz et al, 2002). This ultimately led to the first examples of asymmetric Ni(0)-mediated allylic amination chemistry and to the first asymmetric base metal-mediated synthesis of L-vinylglycine (Berkowitz and Maiti, 2004; Berkowitz et al, 2004).…”