Pchiral hydroxy phosphorus Pboranes

Yeast Infection No More

Best Home Remedy for Candida

Get Instant Access

Among the useful chiral organophosphorus compounds, the trivalent derivatives play a special role. They are used both as chiral auxiliaries in stoichiometric reactions and as chiral ligands in transition metal catalysts. However, trivalent phosphorus compounds are prone to oxidation and usually difficult to handle. Therefore, their borane complexes, which are stable and which can be easily converted into the parent compounds without racemization, are becoming more and more popular.9697 Among various attempts at their synthesis, the enzymatic approach proved suitable for the preparation of chiral non-racemic hydrox-yalkylphosphine P-boranes. Thus, racemic hydroxyalkylphosphine P-boranes rac-85 were subjected to stereoselective acetylation in the presence of various enzymes. As a result of a kinetic resolution, both the unreacted alcohols 85 and acetylation products 86 were obtained in reasonable yields but with moderate ees only (Equation 41, Table 9). The ee values were higher for the same substrates when the reaction was performed in a highly non-polar solvent -cyclohexane.98'99

Also, desymmetrization of prochiral hydroxyalkylphosphine P-boranes was successfully performed using similar reagents and conditions. In the case of bis(hydroxymethyl)phenylphosphine P-borane 87, both its acetylation and hydrolysis of the diacetyl derivative 89 gave good results, although in addition to the expected monoacetate 88, the diol 87 and diacetate 89 were always present in the reaction mixture (Equation 42).100

Lipase

Method

Product distribution

Monoacetate 88

87:88:89

ee (%)

Abs. conf.

ANL

A

63:36:1

70

R

BCL

A

75:23:2

21

R

PPL

A

65:34:1

21

R

PFL

A

41:53:6

62

R

CAL-B

A

0:48:52

92

R

CAL-B

B

48:49:3

90

S

Lipase: ANL, lipase from Aspergillus niger; BCL, lipase from Burkholderia cepacia (formerly Pseudomonas cepacia); CAL-B, lipase from Candida antarctica B; PFL, lipase from Pseudomonas fluorescens; PPL, pig pancreatic lipase.

Lipase: ANL, lipase from Aspergillus niger; BCL, lipase from Burkholderia cepacia (formerly Pseudomonas cepacia); CAL-B, lipase from Candida antarctica B; PFL, lipase from Pseudomonas fluorescens; PPL, pig pancreatic lipase.

In turn, bis(2-hydroxyethyl)phenylphosphine P-borane 90 underwent acety-lation only in the presence of the lipase from Pseudomonas fluorescens, but its stereochemical outcome depended on the solvent used (Equation 43). The absolute configuration of 91 was not determined.99

Solvent Monoacetate 91

CHCl3 43 -10 90

Was this article helpful?

0 0
Natural Remedy For Yeast Infections

Natural Remedy For Yeast Infections

If you have ever had to put up with the misery of having a yeast infection, you will undoubtedly know just how much of a ‘bummer’ it is.

Get My Free Ebook


Post a comment