An efficient chemoenzymatic method to prepare optically active O-methyl-l-serine

O-Methyl-l-serine and its derivatives are relevant in peptide synthesis (food, pharmaceuticals, and cosmetics). Optically active O-methyl-l-serine was prepared using a chemoenzymatic method from inexpensive acrylamide. Our method is a four step reaction sequence; bromination of acrylamide; etherification of dibromopropionamide; ammonolysis of α-bromo-β-methoxy-propionamide; enzymatic racemization; and selective hydrolysis. The double-enzyme catalyst system, which consists of α-amino-ε-caprolactam racemase (Locus, E01594) and peptidase B (Locus, D84499), was successfully applied to produce enantiopure O-methyl-l-serine (ee >99.9%) in high yield (>99.7%). Optically active O-methyl-l-serine was obtained with a total yield of 82.4%.     

The racemization of an optically active sulfilimine and optically active aminosulfonium salts

The racemization of an optically active sulfilimine and optically active aminosulfonium salts was kinetically measured. The mechanism of the racemization of optically active sulfilimine (?)-1 has been established. The activation parameters for the racemization of (?)-1 and (?)-7 were calculated. A plausible pathway for the decomposition of (?)-6, (?)-7 and (?)-8 with tetra-n-butylammonium bromide in the presence of methyl ethyl ketone to provide 3-p-tolylthio-2-butanone 22 is proposed.     

Stereoselective synthesis of optically active cyclitol precursors via a chemoenzymatic method

Racemic α′-acetoxy α,β-unsaturated cyclohexanone has been converted to the corresponding enantiomerically enriched α′-hydroxylated and acetoxylated compounds with 97% ee via enzymatic resolution with PLE. OsO₄-Catalyzed dihydroxylation of enantiomerically enriched α′-acetoxylated compound afforded a single diastereomer in 85% chemical yield. The absolute configuration of 2,3,6-triacetoxycylohexanone was determined by X-ray diffraction analysis. Subsequent Luche reduction allowed us to obtain corresponding syn-type cyclitol precursors in a highly stereoselective manner as expected.     

Synthesis of optically active bihelicenols

All six stereoisomers of dimethyl 5,5′-dihydroxy-1,1′,12,12′-tetramethyl-[6,6′]bi(benzo[c]phenanthrenyl)-8,8′-dicarboxylate (bihelicenol) were synthesized by the oxidative coupling of methyl 8-hydroxy-1,12-dimethylbenzo[c]phenanthrene-5-carboxylate (helicenol), and their structures were determined by X-ray analysis.     

Synthesis of optically active penems

A general synthesis for optically active penems is described. Penems undergo a novel thermal isomerisation reaction.     

Synthesis of optically active lipoaminoacids

Conclusions S--(Distearoyl-L-phosphatidyl)--L-alanylglycerol and its R-isomer have been synthesized.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 6, pp. 1098–1100, June, 1966.     

Pyridylethylation of optically active amines

Summary A study has been made of the addition of (R)- and (S)-1 phenylethylamines and (R)- and (S)-1cyclohexylethylamines to the C=C bond of 2- and 4-vinylpyridines in the presence of an acid catalyst. The corresponding monoadducts have been synthesized with high preparative yields. By reactions of these adducts with 2- and 4-vinylpyridines, bis-adducts have been obtained. All of the products had high optical purities (9199%, HPLC).Institute of Organic Catalysis, Rostock City University, Rostock 18055. Latvian Institute of Organic Synthesis, Riga LV-1006. Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 6, pp. 843–850, June, 1995. Original article submitted May 10, 1995.     

Synthesis of optically active tetrahydrozerumbone

Tetrahydrozerumbone 2, which has a powerful balmy fragrance, has a stereogenic carbon at C2 and can be easily prepared from zerumbone 1, which is one of the most important materials that displays an NMRDOS character. Reduction of 2 gave two diastereomers 3 and 4; their optically active (>99% ee) alcohols were obtained by lipase-catalyzed stereoselective transesterification of each racemic alcohol. The enantioselectivity of tetrahydrozerumbol does not entirely depend on the hydroxyl position but on the 2-methyl position. Compounds (R)-2 and (S)-2 were obtained by Dess–Martin oxidation of the corresponding alcohols. Interestingly, (R)-2 showed a strong balmy fragrance while (S)-2 had hardly any fragrance.     

Synthesis of optically active hydroxyphosphonates

The reduction of dimenthyl ketophosphonates with sodium borohydride involves asymmetric induction at the α‐carbon atom, resulting in a small excess of the (R)‐enantiomer of the α‐hydroxyphosphonate formed. A higher ee purity was achieved if the reduction of chiral dimenthyl ketophosphonates was carried out by the chiral complex of NaBH₄‐L ‐proline, owing to the double asymmetric induction at the α‐carbon atom. The hydroxyphosphonates obtained were isolated in a diastereomerically pure state and were transformed to the optically active, free hydroxyalkylphosphonic acids. The (R)‐configuration of one of them was proved by X‐ray crystal structure analysis. © 2008 Wiley Periodicals, Inc. Heteroatom Chem 19:133–139, 2008; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/hc.20391     

Authenticity assessment: a permanent challenge in food flavor and essential oil analysis

Both phenomena, enantioselectivity as well as isotope discrimination during biosynthesis, may serve as "endogenous" parameters, provided that suitable methods and comprehensive data from authentic sources are available. This review reports on enantioselective capillary gas chromatography and online methods of isotope-ratio mass spectrometry in the authentication of food flavor and essential oil compounds, referring to literature references published in the last decade.     

Development of a chemoenzymatic strategy for the synthesis of optically active and orthogonally protected polyamines

The chemical preparation and stereoselective enzymatic desymmetrization of a series of prochiral 2-substituted-1,3-propanediamines have been carried out using Pseudomonas cepacia lipase as biocatalyst. Syntheses of novel optically active orthogonally protected di- or triamines have been achieved for the first time with different grade of enantiodiscrimination depending on the C-2 substitution of the propane-1,3-diamine fragment. Final monoselective deprotection reactions of (S)-3-allyl-2-tert-butyl-1-(9-fluorenylmethyl)propane-1,2,3-triyltriscarbamate have allowed us to obtain a panel of novel enantiomerically enriched disubstituted triamines, compounds of difficult access by conventional synthetic methods.     

A general method for constructing optically active supramolecular assemblies from intrinsically achiral water-insoluble free-base porphyrins

We have developed a general method to construct optically active porphyrin supramolecular assemblies by using a simple air-water interfacial assembly process. The method involved the in situ diprotonation of the free-base porphyrins at the air-water interface and subsequent assembly under compression. We showed that two intrinsically achiral water-insoluble free-base porphyrin derivatives, 2,3,7,8,12,13,17,18-octaethyl-21H,23H-porphine (H(2)OEP) and 5,10,15,20-tetra-p-tolyl-21H,23H-porphine (H(2)TPPMe), could be diprotonated when spread onto a 2.4 M hydrochloric acid solution surface, and the Langmuir-Schaefer (LS) films fabricated from the subphase exhibited strong circular dichroism (CD) absorption, whereas those fabricated from pure Milli-Q water subphase did not. The experimental data suggested that the helical stacking of the achiral porphyrin building blocks was responsible for the supramolecular chirality of the assemblies. Interestingly, such a method was successfully applied to a series of other intrinsically achiral free-base porphyrins such as 5,10,15,20-tetrakis(4-methoxyphenyl)-21H,23H-porphine (H(2)TPPOMe), 5,10,15,20-tetraphenyl-21H,23H-porphine (H(2)TPP), 5,10,15,20-tetrakis(4-(allyloxy)phenyl)-21H,23H-porphine (H(2)TPPOA), and 5,10,15,20-tetrakis(3,5-dimethoxyphenyl)-21H,23H-porphine (H(2)TPPDOMe). A possible mechanism has been proposed. The method provides a facile way to obtain optically active porphyrin supramolecular assemblies by using intrinsically achiral water-insoluble free-base porphyrin derivatives.     

Synthesis of optically active 5,6,7,8-tetrahydroquinolines

(+)-(R)-5-Methyl- and (+)-(R)-2,5-dimethyl-8-isopropylidene-5,6-dihydro-7H-quinoline, 7 and 11 , were synthesized by reaction of (R)-pulegon morpholino-enamine with acrolein or methyl vinyl ketone. The Michael adducts thus formed were reacted with hydroxylammonium hydrochloride in polar media. Compound 7 was also obtained by thermal rearrangement of the O-allyl ether of pulegone oxime. The selectivity of both synthetic methods were rather poor (30–49%). Isolation of 7 and 11 in the pure state was accomplished by preparative glc.     

Syntheses of optically active trifluoronorcoronamic acids

Syntheses of optically active trifluoronorcoronamic acid 6 and its diastereomer 9 are described. Highly stereospecific and diastereoselective S(N)2 cyclization of gamma-cyanohydrins 3a and 3b gave cyclopropyl nitriles 4a and 4b. Hydrolysis of the cyano group and deprotection of the amino group of 4a provide trifluoronorcoronamic acid 6. Hofmann rearrangement of the amide which was generated by hydrolysis of the cyano group and oxidative cleavage of the aryl ring of 4b to provide trifluoro-allo-norcoronamic acid 9.     

光学活性炔丙醇的合成

具有光学活性的炔丙醇是有机合成的重要中间体，其合成方法较多，通常使用 不对称还原、不对称1，2－加成、动力学拆分、2，3σ－重排、消除、还原裂解等 方法合成，其ee值和化学产率均达到了良好的水平，作者将对这类化合物的不对称 合成方法作一总结。