One‐Pot Deracemization of sec‐Alcohols: Enantioconvergent Enzymatic Hydrolysis of Alkyl Sulfates Using Stereocomplementary Sulfatases

Abstract

Hand in Hand: Die Titelumsetzung gelang mit einem Paar von Sulfatasen, die unter Inversion und Retention der Konfiguration an entgegengesetzten Substrat‐Enantiomeren agieren. Setzt man die Arylsulfatase PAS und die Alkylsulfatase PISA1 im selben Reaktionsansatz ein, entstehen sec‐Alkohole (80 bis >99 % Umsatz) mit 91 bis über 99 % ee.

Enhancing the Steroid Sulfatase Activity of the Arylsulfatase from Pseudomonas aeruginosa

“…From this analysis, it was clear that subtle changes in active site flexibility and the positioning of key residues could have a major impact on enzymatic activity and substrate scope. Significantly, previous experimental 25,26,34,42,43 and computational 33,44,45 studies have focused primarily on smaller model substrates, like pNPS, with activated leaving groups, whereas the present work examines larger steroid substrates of applied interest. Such substrates are notable for two reasons: they incorporate unstabilised leaving groups and so have a strict requirement for general acid catalysis during hydrolysis, and they are large and so more completely fill the PaS active site.…”

Inverting hydrolases and their use in enantioconvergent biotransformations

“…When both enzymes show high enantioselectivity, they can act simultaneously on both substrate enantiomers ( A and ent - A ) in a one-pot protocol. Type-2 reactions have so far been shown for epoxide hydrolases [25–27] and alkyl sulfatases [16].…”

“…Because the second step starts with a single enantiomer A or ent - A (which was not converted in the preceding kinetic resolution step), enantioselectivity is not required. Examples of bi-enzymatic type-3 reactions are known for alkyl sulfatases [16]. Alternatively, chemocatalytic methods may be used for the second (nonenantioselective) step to furnish chemoenzymatic type 3 protocols.…”

“…In addition, benzylic sec -alkylsulfate esters, which also showed severe autohydrolysis, could be stabilized by the presence of electron-withdrawing groups on the aromatic ring (M. Toesch et al, unpublished). A chemoenzymatic deracemization protocol requiring medium change (Figure 2, type 3a) using Pisa1 (in the first step) and acidic hydrolysis ( p -toluenesulfonic acid, MTBE/H 2 O 98:2) in the second step, could be developed (Table 1) [16]. This protocol was successfully applied to 5-hexen-2-yl sulfate as the key step in the total asymmetric synthesis of ( R )-lasiodiplodin methyl ether, a precursor of the anti-leukemic agent lasiodiplodin [42].…”

“…An analogous one-pot two-step protocol was developed for 2-octyl sulfate [41], but its applicability was limited by the strongly acidic reaction conditions. These drawbacks could be circumvented by the discovery of retaining sec -alkyl sulfatase activity for P. aeruginosa arylsulfatase (PAS) [16]. Because the enzyme showed opposite enantiopreference compared with Pisa1, both enzymes could be combined in three different types of one-pot enantioconvergent processes of type 3: In the first case, highly enantioselective inverting Pisa1 yielded a homochiral mixture of formed alcohol and nonconverted sulfate via kinetic resolution.…”