Bård Helge Hoff

Chemo-enzymatic synthesis of the antidepressant duloxetine and its enantiomer

Sodium borohydride reduction of 3-chloro-1-(2-thienyl)-1-propanone gave the corresponding racemic alcohol which was kinetically resolved with lipase B from Candida antarctica as catalyst to yield the chiral building blocks (S)-3-chloro-1-(2-thienyl)-1-propanol and the corresponding (R)-butanoate. The enantiopure chiral building blocks were converted into Duloxetine and its enantiomer.

Resolution of derivatives of 1,2-propanediol with lipase B from Candida antarctica. Effect of substrate structure, medium, water activity and acyl donor on enantiomeric ratio.

The glycerol-related racemic derivatives 1a-15a and 1b-15b have been resolved by hydrolysis and transesterifications using lipase B from Candida antarctica. Influence of substrate structure for the enantiomeric ratio E has been explained on the basis of previous molecular modelling. E values and equilibrium constants Keq have been calculated on the basis of ees and eep measured throughout the reaction, and ping-pong bi-bi mechanism using the computer program E&K calculator. Medium effects have been studied for hydrolysis with organic co-solvents and transesterifications in different solvents with varying water activity, aw. For some substrates addition of 30% acetone to the hydrolysis reaction gave a large increase of E. High water activity gave for some substrates an increase of E, but was unfavourable for the reversibility. However, this did not significantly influence the ee of product fraction. The influence of the alkoxy part of various butanates as acyl donors has been studied with respect to E and Keq. It was generally found that 2-chloroethyl butanate gave higher E than vinyl butanate; however, the latter gave irreversible conditions.

Structure-activity study leading to identification of a highly active thienopyrimidine based EGFR inhibitor.

Based on the thieno[2,3-d]pyrimidine scaffold, a series of new 4-amino-6-aryl thienopyrimidines have been prepared and evaluated as EGFR tyrosine kinase inhibitors. The in vitro activity was found to depend strongly on the substitution pattern in the 6-aryl ring, the stereochemistry, and the basicity at the secondary 4-amino group. A stepwise optimization by combination of active fragments led to the discovery of three structures with EGFR IC50 < 1 nM. The most potent drug candidate had an IC50 of 0.3 nM towards EGFR and its mutants L858R and L861Q. Studies using human cancer cell lines and an EGFR-L858R reporter cell system revealed good cellular potency, verifying the identified thienopyrimidines as promising lead structures.

Enantioselective enzymatic preparation of chiral glutaric monocarboxylic acids and amides

Enantioselective hydrolyses and ammonolyses of diethyl-3-hydroxyglutarate (1) and dimethyl-3-hydroxyglutarate (2) gave a maximum of 91 and 98% enantiomeric excess (ee), respectively, using immobilized lipase B from Candida antarctica. The ees were determined using chiral GLC of the monoamides and achiral GLC of diasteromeric derivatives of the monocarboxylic acids. The catalyst was re-used more than 10 times with retention of high activity and selectivity.

Calculation of enantiomer ratio and equilibrium constants in biocatalytic ping-pong bi-bi resolutions

Abstract A computer program for the determination of kinetic and thermodynamic parameters in biocatalytic ping-pong bi-bi resolutions has been developed. The program uses enantiomeric excesses of both product ( ee p ) and remaining substrate ( ee s ) measured at more than one conversion (ξ), and determines both the equilibrium constant K eq , the enantiomer ratio E and the selectivity factor α. The program has been tested for transesterification of 1-phenoxy-2-propanol using different excesses of acyl donor.

Synthesis and in vitro EGFR (ErbB1) tyrosine kinase inhibitory activity of 4-N-substituted 6-aryl-7H-pyrrolo[2,3-d]pyrimidine-4-amines

A series of 4-N-substituted 6-aryl-7H-pyrrolo[2,3-d]pyrimidine-4-amines have been synthesised, characterised and tested for their in vitro EGFR (ErbB1) tyrosine kinase inhibitory activity. The compounds were prepared from ethyl cyanoacetate and α-bromoacetophenones via the 2-amino-3-ethoxycarbonyl-5-aryl-pyrroles and 4-chloro-6-arylpyrrolopyrimidines. Aromatic substitution with benzylic amines was performed by conventional thermal substitution, and palladium catalysed coupling. The two methods resulted in similar yields, but the palladium coupling had the benefit of lower chemical consumption and reduced reaction times. Eight of the new compounds had IC(50) values in the range of 2.8-9.0 nM. Four of these have a fluorine atom positioned at sites otherwise potentially susceptible to oxidative metabolism. Structural variation of the 6-aryl group indicated that the inhibitory action was only moderately sensitive to modifications in this fragment. However, the potency depended strongly on the structure of the aromatic part of the 4-amino group, and any aromatic substitution except fluorine reduced the in vitro activity. The cellular EGFR internalization response of selected compounds was evaluated using HeLa cells. Three fluorinated derivatives had a pronounced effect in inhibiting EGFR internalization.

The enantiomer ratio strongly depends on the alkyl part of the acyl donor in transesterification with lipase B from Candida antarctica

Abstract Three secondary alcohols, 1-phenoxy-, 1-phenylmethoxy- and 1-(2-phenylethoxy)-2-propanol, have been resolved by transesterification with the acyl donors 2-chloroethyl butanoate, 2,2,2-trichloroethyl butanoate, vinyl butanoate and butanoic anhydride using lipase B from Candida antarctica as catalyst in hexane. The enantiomer ratio E , which was calculated on the basis of a ping-pong bi-bi mechanism, was highest when 2-chloroethyl butanoate was used as acyl donor, however the reaction was reversible. It was shown that the E -value increased when the amount of 2,2,2-trichloroethyl butanoate was reduced. It is also indicated that butanoic anhydride and vinyl butanoate make the lipase less specific probably by acylation.

Resolution of 1-phenoxy-, 1-phenylmethoxy- and 1-(2-phenylethoxy)-2-propanol and their butanoates by hydrolysis with lipase B from Candida antarctica

Abstract Resolutions of butanoic esters of 1-phenoxy-2-propanol, 1-phenylmethoxy-2-propanol and 1-(2-phenylethoxy)-2-propanol have been studied with four different lipases as catalysts. Using lipase B from Candida antarctica very high enantiomer ratios were obtained. These substrate-lipase pairs represent an excellent way of getting enantiomerically pure protected 1,2-propanediols in high chemical yield.

Extended structure–activity study of thienopyrimidine-based EGFR inhibitors with evaluation of drug-like properties

Thieno[2,3-d]pyrimidines are attractive derivatives for cancer treatment, among others through regulation of the epidermal growth factor receptor tyrosine kinase (EGFR-TK). In an extended SAR study, 44 new compounds of this class have been evaluated as inhibitors, while simultaneously focussing on ADME properties. Through the application of bioisosters, hybrid structures, solubilizing tails, and a combination approach several successful alterations in terms of activity and physiochemical properties were accomplished. Compounds based on benzylamines were found superior to aniline hybrid structures with respect to activity and ADME profile. Exploration of the former class revealed meta- and para amides as favourable 6-aryl substituents, contributing to an increase in activity and acting as a linker for solubilizing tails. Next, combinations of activity-inducing groups on the same scaffold resulted in new drug candidates. Compounds containing 6-aryls with the (2-(dimethylamino)ethyl)carbamoyl substituent were found equipotent to Erlotinib. Compared to this commercial drug, improved solubility and metabolic stability were observed. However, the thieno[2,3-d]pyrimidines with a solubilizing tail was by Caco-2 experiments found to have permeability issues, making further drug development difficult. Selected compounds were further analysed for toxicity and teratogenicity in zebrafish embryos. Two thienopyrimidines were both found to be less lethal than Erlotinib and to perform as well in terms of teratogenicity. Finally, the most promising thienopyrimidine drug was evaluated in a panel of human cancer cell lines, showing a clear potential for thienopyrimidines as anti-cancer agents.

Gas chromatographic enantiomer separation of C-3 and C-4 synthons: Prediction of absolute configuration from elution order and enzymatic resolution

Enantiomers of C-3 secondary alcohols, 3-hydroxybutanoates, and cyclic 1,3-dithioacetals were separated by chiral GLC using CP-Chirasil-Dex CB and Chiraldex G-TA columns. The former was most successful for analysis of n-alkyl esters of secondary alcohols and the separation depended on the chain length of the acyl group and the electronic and steric properties of the other substituents. The Chiraldex G-TA column was efficient for analysis of secondary alcohols, derivatized as their trifluoroacetates. The elution order of the secondary alcohols and the corresponding acetates was always the same with respect to the size of groups connected to the stereocenter. However, when the secondary alcohols were analyzed as their trimethylsilyl derivatives, the elution order was reversed. Elution order on chiral columns and enantiomeric ratios, E-values, obtained in kinetic resolutions catalyzed by lipase B from Candida antarctica (CALB) were evaluated as a method for prediction of absolute configuration. The usefulness of the method was demonstrated using 22 pairs of enantiomers. Copyright 1999 Wiley-Liss, Inc.