J. Augusto R. Rodrigues

Regioselectivity of the nitration of phenol by acetyl nitrate adsorbed on silica gel

Abstract The reaction of phenol with acetyl nitrate in chloroform gives nitrophenol with an ortho/para ratio of 1.8. This ratio increase to 13.3 when the reaction was carried out with acetyl nitrate pre-adsorbed on dry silica gel. Silica may be acting as a template to bring phenol close to acetyl nitrate by hydrogen bonds forming a ternary complex, which undergoes a six-center rearrangement to o-nitrophenol. The formation of this ternary complex is evaluated by ab initio molecular orbital calculation.

Effect of immobilized cells in calcium alginate beads in alcoholic fermentation

Saccharomyces cerevisiae cells were immobilized in calcium alginate and chitosan-covered calcium alginate beads and studied in the fermentation of glucose and sucrose for ethanol production. The batch fermentations were carried out in an orbital shaker and assessed by monitoring the concentration of substrate and product with HPLC. Cell immobilization in calcium alginate beads and chitosan-covered calcium alginate beads allowed reuse of the beads in eight sequential fermentation cycles of 10 h each. The final concentration of ethanol using free cells was 40 g L-1 and the yields using glucose and sucrose as carbon sources were 78% and 74.3%, respectively. For immobilized cells in calcium alginate beads, the final ethanol concentration from glucose was 32.9 ± 1.7 g L-1 with a 64.5 ± 3.4% yield, while the final ethanol concentration from sucrose was 33.5 ± 4.6 g L-1 with a 64.5 ± 8.6% yield. For immobilized cells in chitosan-covered calcium alginate beads, the ethanol concentration from glucose was 30.7 ± 1.4 g L-1 with a 61.1 ± 2.8% yield, while the final ethanol concentration from sucrose was 31.8 ± 6.9 g L-1 with a 62.1 ± 12.8% yield. The immobilized cells allowed eight 10 h sequential reuse cycles to be carried out with stable final ethanol concentrations. In addition, there was no need to use antibiotics and no contamination was observed. After the eighth cycle, there was a significant rupture of the beads making them inappropriate for reuse.

Baker's yeast reduction of α-haloacetophenones

Abstract The fermenting bakers yeast reductions of α-haloacetophenones were carried out by three different procedures. While the α-fluoro-, α-chloro- and α-bromoacetophenones gave the correspondent (−)-halohydrins, the reduction of α-iodoacetophenone gave acetophenone and (−)-1-phenylethanol.

Highly efficient extractive biocatalysis in the asymmetric reduction of an acyclic enone by the yeast Pichia stipitis

Abstract A concise highly chemo- and enantioselective preparation of ( S )-2-ethyl-1-phenylprop-2-en-1-ol 6 (65% yield, >99% e.e.) via extractive biocatalysis by the yeast Pichia stipitis CCT 2617-mediated reduction of 2-ethyl-1-phenylprop-2-en-1-one 5 adsorbed on Amberlite™ XAD-7 is reported.

Continuous process for large-scale preparation of chiral alcohols with baker's yeast immobilized on chrysotile fibers

Abstract Bioreductions of prochiral ketones in a continuous process were carried out in a Packed-bed-reactor with bakers yeast ( Saccharomyces cerevisiae ) immobilized on chrysotile fibers (IMBY). The performance of the reactor was observed for 30 days, under a constant dilution rate of 1.7×10 −1 h −1 using ethylbenzoylformate as substrate. The steady state showed 2.9×10 −2 g l −1 h −1 of productivity, 50% chemical yield, and 90% ee (enantiometric excess). Using ethylacetoacetate at the same dilution rate for 8 days, the steady state showed 65% chemical yield and 95% ee. No significant change on the IMBY integrity was observed. The results show that chrysotile is an excellent carrier for immobilization of bakers yeast (BY) cells to be used in the continuous process of bioreduction

Baker's yeast reduction of α-methyleneketones

Abstract The bioreduction of α-methyleneketones, R 1 C(O)C(CH 2 )R 2 (R 1 =Me, Et, Pr, iso- Bu, Ph, CH 2 CH 2 Ph; R 2 =Cl, Me, Et, n- Pr, iso- Pr, n- Bu, n- C 6 H 13 , Ph, CH 2 Ph), was mediated by bakers yeast ( Saccharomyces cerevisiae ) to obtain the corresponding α-methylketones. The R 1 and R 2 groups had a significant influence on the rate and enantioselectivity of the reductions. The rate of CC bond reduction was higher than that of CO bond reduction. Only α-methyleneketones having R 1 =Me yielded α-methylketones in high enantioselectivity with e.e.s of 88–99%.

Characterization of Saccharomyces cerevisiae immobilized onto chrysotile for ethanol production

Saccharomyces cerevisiae (CCT 3174 and commercial bakers yeast) was immobilized by adsorption onto chrysotile. The adsorbed yeast cells were easily washed out, but cells grown in situ were strongly attached by entrapment by chrysotile microfibres. In fermentation experiments with 30% (w/v) glucose solution, the immobilized cells showed a 1·3-fold increase in initial reaction velocity. For immobilized CCT 3174, the final ethanol yield was 26% higher than that with free cells.

Baker's yeast reduction of (E)-1-phenyl-1,2-propanedione 2-(O-methyloxime). A key step for a (−)-norephedrine synthesis

Abstract The enantioselective Bakers yeast reduction of (E)-1-phenyl-1,2-propanedione 2-(O-methyloxime) 1 afforded (−)-(R)-1-hydroxy-1-phenyl-2-propanone 2-(O-methyloxime) 2 with 97% of enantiomeric excess (ee) which was diastereoselectively reduced by LiAlH4 to obtain the (−)-(R,S)-norephedrine with ee=82% and (−)-(R,R)-norpseudoephedrine with ee=93% in a ratio 4:1 respectively.

Hydride transfer versus electron transfer in the baker's yeast reduction of α-haloacetophenones

Abstract The bakers yeast reduction of α-iodoacetophenone gave acetophenone. Some evidence for a free radical chain process in this reduction was obtained by addition of DNB which not only provoked a decrease in the formation of acetophenone but also allow the appearance of the enzyme-controlled formation of (−)-(R)-2-iodo-1-phenylethanol.

Preparation of α-Methylene Ketones by Direct Methylene Transfer

Abstract Four methods for the preparation of α-methylene ketones by direct methylene transfer are presented. The procedures were optimized in order to obtain high yields.