L- -ephedrine

Reaction of the enantiomerically pure alkoxyamines 3, prepared from L-ephedrine or norephedrine derivatives 1 with acetaldehyde, isobutyraldehyde or benzaldehyde using ethanol as the solvent, afford the corresponding oxime ethers 4 as mixtures of E/Z-stereoisomers11. 

C,4H2f,03 626-27-7) see Norethisterone enanthate Prasterone enanthate testosterone enanthate l.-ephedrine... 

The asymmetric synthesis of 2-aryl(alkyl)-l,3,2-oxazaphospholidines 52 was based on the reaction of achiral organophosphonous diamides 51 with L-ephedrine (42) (Scheme 19) [44], The diastereomeric excess ranges from 0% (R=Ph) to 95%... 

Ephedrine was originally isolated as the active agent present in plant extracts used in ancient Chinese medicine for respiratoiy ailments. As long ago as 1921 the formation of optically active phenylacetyl carbinol (PAC) from benzaldehyde and pyravate by brewers yeast and cell-free yeast extracts was reported. The PAC can then be reductively animated to produce optically active L-ephedrine (Figure 4.18). L-Ephedrine is widely used in the treatment of asthma and hay fever as a bronchodilating agent and decongestant. 

L-Ephedrine is a well accepted and widely used drag so that markets are significant. 

Rogers, P.L., Shin, H.S. and Wang, B. (1997) Biotransformation for L-ephedrine production. Advances in Biochemical Engineering, 56, 33-59. 

With benzaldehyde 144 or halogenated derivatives (Cl, F) as acceptors the yeast-PDC-catalyzed addition proceeds with almost complete stereoselectivity to furnish the corresponding (R)-configurated 1-hydroxy-1-phenylpropanones 145 [447]. For practical reasons, whole yeast cells are most often used as the catalyst, with only small loss of enantioselectivity [423,424]. The conversion of benzaldehyde in particular has gained industrial importance because the acyloin is an important precursor for the synthesis of L-(-)-ephedrine [448]. Otherwise, the substrate tolerance is remarkably broad for aromatic aldehydes on the laboratory scale, however, yields of acyloins are usually low because of the prior or consequent reductive metabolism of aldehyde substrate and product, giving rise to considerable quantities of alcohol 146 and vicinol diols 147, respectively [423,424,449], The range of structural variability covers both higher a-oxo-acids (e.g. -butyrate, -valerate) as the donor component, as well as a,/J-un-saturated aldehydes (e.g. cinnamaldehyde 148) as the acceptor [450]. 

Chiral formylcyclopropanes.2 The oxazolidine (1), obtained by reaction of cinnamaldehyde with l>-( -)-ephedrine, reacts with diazomethane [Pd(OAc)2 catalysis] to give 2 in at least 90% ee. Hydrolysis of 2 to 3 is effected by moist SiO,. It is also possible to prepare cyclopropanes with three chiral centers, such as 5. 

Optimization of a continuous enzymic reaction yielding (R)-phenylacetylcarbinol (PAC), an L-ephedrine intermediate (Chapter 7, Section 7.5.2), from acetaldehyde and benzaldehyde with PDC from Zymomonas mobilis demonstrated that... 

The production of (-R)-PAC by fermenting yeast was one of the first industrially applied biotransformations, which is used to nowadays to obtain (R)-PAC as a chiral pre-step for L-ephedrine 2 [6-9] (Scheme 1), and the optimization of the fermentation process is still a matter of research [10 23],... 

Enantiomerically pure mandelic acid has also been prepared by resolution of the racemic substance through the formation of a dissociable diastereomer with ephedrine [5]. In a typical preparation, 12 g of (L)-ephedrine and 12 g of racemic mandelic acid are heated together in 40 mL of 90% ethanol. The diastereomer salt is obtained upon cooling of the solution, and may be purified by recrystallization from a small volume of alcohol. )-... 

The enzymic oxidative deamination of simple phenethylamines is exemplified by the reported bio transformations of mescaline (146) (114, 115) and ephedrine (148) (116). Mescaline is metabolized to 3,4,5-trimethoxy-phenylacetic acid by tissue homogenates of mouse brain, liver, kidney, and heart (114,115). 3,4,5-Trimethoxybenzoic acid is also formed as a minor metabolite. The formation of jV-acetylmescaline (147), a significant metabolite in vivo, was not observed in the in vitro studies. Both D-(—)-and L-(+)-ephedrine have been incubated with enzyme preparations from rabbit liver norephedrine (149), benzoic acid, and 1-phenyl-1,2-propanediol were characterized as metabolites (116). The D-(—)-isomer was the better substrate, being more rapidly converted. Similar results were previously reported with rabbit liver slices as the source of enzyme (153,154). The enzymic degradation of the side chain of /i-phenethylamines has been extensively investigated with nonalkaloid substrates such as amphetamine (151) and jV-methylamphetamine (150) (10,155-157), and the reader is referred to these studies for a more comprehensive coverage of this aspect of the subject. 

The a-keto acid decarboxylases such as pyruvate (E.C. 4.1.1.1) and benzoyl formate (E.C. 4.1.1.7) decarboxylases are a thiamine pyrophosphate (TPP)-dependent group of enzymes, which in addition to nonoxidatively decarboxylating their substrates, catalyze a carboligation reaction forming a C-C bond leading to the formation of a-hydroxy ketones.269-270 The hydroxy ketone (R)-phenylacetylcarbinol (55), a precursor to L-ephedrine (56), has been synthesized with pyruvate decarboxylase (Scheme 19.35). BASF scientists have made mutations in the pyruvate decarboxylase from Zymomonas mobilis to make the enzyme more resistant than the wild-type enzyme to inactivation by acetaldehyde for the preparation of chiral phenylacetylcarbinols.271... 

C7H6() 100-52-7) see Acetorphan Amphetaminil Atorvastatin calcium Azimilide hydrochloride Benzathine benzylpenicillin Docetaxel L(-)-Ephedrine Ethotoin Fenipentol Fenquizone Furazolidone Imolamine Isocarboxazid Metamizole sodium Oxacillin Paclitaxel Phensuximide Phentermine Pildralazine Propiverine benzaldehyde [6-[(2-hydroxypropyl)methylamino]-3-py-ridazinyl]hydrazone... 

Two new stereospecific syntheses of L-ephedrine were reported in 1984. Reduction of the N-protected amino ketone 5 with dimethylphenylsilane in trifluoro-acetic acid (TFA) gave the N-protected amino alcohol 6 with high (>99%)... 

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