Enzymatic Removal of Carboxyl Protecting Groups. III. Fast Removal of Allyl and Chloroethyl Esters by Bacillus subtilis Esterase (BS2)

Abstract

An esterase from Bacillus subtilis (BS2) allows the fast and selective removal of allyl, 2-chloroethyl, and 2,2,2-chloroethyl esters under mild conditions in high yields. In addition, BS2 easily hydrolyzes phenacyl esters, while the hydrolysis of sterically hindered diphenylmethyl esters is slow, requiring longer reaction time and higher enzyme/substrate ratio.

Bacillus subtilis Esterase (BS2) and its Double Mutant Have Different Selectivity in the Removal of Carboxyl Protecting Groups

“…We have previously demonstrated the quick hydrolysis of the allyl ester of Z-GABA (Z-GABA-OAll) by BS2. [11] The double mutant E188W/ M193C quickly hydrolyzed this ester within 15 min. The curves for their hydrolysis are included in Figure 1 and Figure 2.…”

“…The hydrolysis of these esters and the corresponding ethyl ester [11] 1a by BS2 in a mixture of buffer/hexane (9:1) containing a small amount of methanol was studied. Their hydrolysis was monitored by HPLC and the results are presented in Figure 1.…”

“…After removal of DMF, EtOAc (20 mL) was added, the organic layer was washed consecutively with a saturated solution of NaHCO 3 , water and brine, dried over Na 2 SO 4 The syntheses of substrates 1a and 3c were described previously. [11] General Procedure for the Enzymatic Hydrolysis…”

“…[9] In addition, we have reported that BS2 was a versatile agent for the efficient removal of a variety of carboxyl protecting groups under mild conditions that avoid side reactions. [10,11] Point mutations in BS2 had a remarkable influence on both activity and enantioselectivity. [12] Most interestingly, the double mutant E188W/M193C of BS2 presented complete inversion of enantioselectivity towards acetylated tertiary alcohols.…”

Chemoenzymatic Synthesis of Both Enantiomers of 2‐tert‐Butyl‐2‐methyl‐1,3‐benzodioxole‐4‐carboxylic (TBMB) Acid

“…To enhance the enzyme activity of the ester, particularly of the "fast" (R)-isomer, the methyl substituent was replaced with the more electron-withdrawing chloroethyl ester group. [3] The reaction with substrate 1c proceeded at lower temperature (30 8C), indicating that the activity was indeed enhanced; however, the selectivities were disappointing. All of the hydrolytic enzymes (Table 1, entries 3-5) showed low enantioselectivities.…”