羰基还原酶CR2重组酶体系不对称合成(S)-N,N-二甲基-3-羟基-3-(2-噻吩)-1-丙胺

构建了羰基还原酶CR2重组酶体系,并优化了相关的酶促催化反应条件.通过在催化体系中添加辅酶NADP+(0.1 mmol/L)和辅底物葡萄糖(120 g/L),在30℃及p H=8.0的条件下反应4 h,CR2重组酶体系不对称还原N,N-二甲基-3-酮-3-(2-噻吩)-1-丙胺(DKTP,10 g/L),合成了高光学纯度(S)-N,N-二甲基-3-羟基-3-(2-噻吩)-1-丙胺[(S)-DHTP,e.e.值99.9%],产率为62%.在酶促催化过程中,由于辅酶循环生成葡萄糖酸导致反应体系p H值下降而影响催化效率.通过调控反应体系p H值,(S)-DHTP的产率提高到68%.不同浓度底物的反应过程表明底物对CR2酶促反应具有抑制作用,且在10 g/L底物浓度下反应的时空产率可达1.3 g·L-1·h-1.     

微波辅助铜合成2-(N,N-二甲氨基)苯并噁唑衍生物

建立了一种简单实用、经济高效的以取代2-碘芳胺和N,N-二甲基氨基硫代甲酰氯为原料,以碘化亚铜为催化剂,吡啶为溶剂,100 ℃条件下,串联合成2-(N,N-二甲氨基)苯并噁唑衍生物的微波催化体系,合成了一系列中等至良好产率的2-(N,N-二甲氨基)苯并噁唑衍生物,最高产率达90%。     

A totally stereocontrolled route to N-methyl-γ-amino-β-hydroxy acids: Asymmetric synthesis of the amino acid component of hapalosin

A new approach to the synthesis of N-methyl-γ-amino-β-hydroxy acids, compounds that are essential components of several depsipeptides exhibiting highly interesting therapeutic profiles, is presented. Relevant steps in the synthetic sequence involve the totally stereoselective preparation of a protected aminoalkyl epoxide from a highly enantiopure 2,3-epoxy alcohol, efficient N-methylation and three-step conversion to the desired N-methyl amino acid. The method is exemplified by the enantioselective synthesis of (3R,4S)-4-(N-methylamino)-3-hydroxy-5-phenylpentanoic acid in two differently protected forms.     

Asymmetric silyl nitronate cycloadditions with bornane-10,2-sultam derivatives

Asymmetric silyl nitronate cycloadditions with N-acryloyl (2R)-bornane-10,2-sultam, N-acryloyl (2S)-bornane-10,2-sultam, and N-methacryloyl (2R)-bornane-10,2-sultam have been studied. The asymmetric silyl nitronate cycloaddidon/elimination methodology provides a general route for the asymmetric synthesis of 2-isoxazolines.     

Synthesis of new enantiomerically pure C1- and C2-symmetric N-alkyl-benzimidazolium and thiazolium salts

Starting from the commercially available enantiopure (1S,2S)-2-amino-1-phenyl-1,3-propanediol novel enantiomerically pure benzimidazoles were prepared; N-alkylation gave chiral benzimidazolium salts, which were tested in asymmetric benzoin condensations. The synthesis of conceptually new, enantiomerically pure, C₂ symmetric bis-thiazolium and bis-benzimidazolium salts was also developed. These new chiral heterocycles were employed as catalysts in the asymmetric dimerisation of benzaldehyde to give benzoin with moderate enantioselectivity.     

Chemoenzymatic synthesis of enantiomerically pure terminal 1,2-diols

A new practical method for the enzymatic synthesis of 1,2-diols has been developed by employing a lipase catalyzed one-pot transesterification protocol. A series of substituted -acetoxyphenylethanones 3a–g have been reduced to the corresponding alcohols under mild conditions employing sodium borohydride and moist neutral alumina, and further subjected for lipase catalyzed irreversible transesterification in the same pot to give mono- and diacetate diols (R)-4 and (S)-5, which on hydrolysis afforded terminal 1,2-diols, (R)- and (S)-6 in high enantiomeric excess.     

Stereoselective synthesis of (1R,2S)-2-amino-1,3-diols from (R)-cyanohydrins

Vinyl substituted (1R,2S)-amino alcohols 5 were obtained by addition of vinyl magnesium bromide to the corresponding cyanohydrin O-trimethylsilyl ethers (R)-2. The O- and N-protected vinyl amino alcohols 6 were ozonized at −78°C in methanol yielding (1R,2S)-2-amino-1,3-diols7 in high enantiomeric and diastereomeric excesses. For purification, compounds 7 in some cases were acetylated to give the derivatives (1R,2S)-8. Racemic 6a was converted by oxidative ozonolysis at −78°C in methanolic NaOH solution to the corresponding methyl N-acetyl-β-hydroxy propanoate 9a. The configuration of (1R,2S)-8a was confirmed by x-ray crystallographic analysis.     

Metal complexes of biologically important ligands: Synthesis of amino acidato complexes of Pd containing a C,N-cyclometallated group as an ancillary ligand

New amino acidato complexes of Pd^II of stoichiometry [Pd(C---N)(Aa)] (C---N=C,N-cyclometallated ligand, Aa = N,O-amino acidato ligand) have been obtained by reaction of [Pd(C---N)(acac)] (C---N=N,N-dimethylbenzylamine-C²,N (dmba) (1) or N,N-dimethyl(S--phenylethyl)amine-C²,N (S-dmphea) (2)) with glycine, chiral amino acids (alanine, phenylalanine and valine), and amino acid derivatives (N-acetylglycine and N-acetyl-,β-dehydroalanine) in MeOH. The compounds are characterized by IR, ¹H and ¹³C NMR. The geometry of these complexes has been unambiguously determined by NOE difference experiments and NOESY measurements.     

Reverse enantioselectivity in the lipase-catalyzed desymmetrization of prochiral 2-carbamoylmethyl-1,3-propanediol derivatives

Enantioselective acetylation of 2-carbamoylmethyl-1,3-propanediol derivatives was catalyzed effectively by lipase PS to give monoacetates with high enantioselectivity: The enantioselectivity depended on the 2-carbamoylmethyl groups. The reaction of N-monoalkylcarbamoylmethyl-1,3-propanediol afforded the monoacetate with the (S)-configuration, whereas N,N-dialkylcarbamoylmethyl-1,3-propanediol gave the monoacetate with the (R)-configuration.     

Diastereoselective allylation of N-glyoxyloyl-(2R)-bornane-10,2-sultam and (1R)-8-phenylmenthyl glyoxylate: synthesis of (2S,4S)-2-hydroxy-4-hydroxymethyl-4-butanolide

The diastereoselective addition of allylsilanes and allylstannanes to N-glyoxyloyl-(2R)-bornane-10,2-sultam 1 and (1R)-8-phenylmenthyl glyoxylate 7 in the presence of Lewis acids has been studied. We obtained diastereoselectivities up to 84% and 94% for the allylation of 2 and 7, respectively. The application of the allylation products of 1 or 2 in the synthesis of 4-butanolides, for example (2S,4S)-2-hydroxy-4-hydroxymethyl-4-butanolide 13 is presented.     

Chiral ferrocenyl amidophosphine ligand for highly enantioselective addition of diethylzinc to N-diphenylphosphinoylimines

The asymmetric addition of diethylzinc to N-diphenylphosphinoylimines afforded N-diphenylphosphinoylamides with enantioselectivity of up to 90% ee in the presence of a catalytic amount of chiral ligand (S)-N-ferrocenoyl-2-[(diphenylphosphino)methyl]-pyrrolidine 13 (7 mol %) and Cu(OTf)₂ (15 mol %). The remarkable improvement of enantioselectivities, as compared with the same type of chiral ligand 6, could be explained by the unique structure of ferrocenyl amidophosphine ligand combining with the reactive intermediate of this addition reaction.     

Chiral Non-racemic Bis(vicinal 1,2-Diamines): 4,5-Diamino-N-(3,4-diaminobutyl)pentanamide Tetrahydrochloride, N,N′-Bis[3,4-bis (t-butoxycarbonylamino)butyl]urea and N,N′Bis

The reaction of (R) or (S)-N⁴,N⁵-bis(t-butoxycarbonyl)-4,5-diaminopentanoic acid (6) with (R) or (S)-N³,N⁴-bis(t-butoxycarbonyl)-3,4-diaminobutylisocyanate (8) catalyzed by 4-dimethylamino pyridine (DMAP), leads to the synthesis of (R,R), (S,S), (R,S) and (S,R) isomeric amides (11 a — d) The addition of adipic acid monomethyl ester to (R) or (S) isocyanate, followed by saponification, acidification and subsequent reaction with the second molecule of (R) or (S) isocyanate allows isolation of the (R,R), (S.S) and the meso isomers of N,N′-bis[3,4-bis(t-butoxycarbonylamino) butyl]hexanediamide (17) Removal of protecting groups with HCl/EtOH affords chiral non-racemic molecules having two free vicinal diamine units.     

Asymmetric alcoholysis of 2-phenyl-5(4H)-oxazolones by the catalytic mixture of cyclo[(S)-His-(S)-Phe] with chiral auxiliaries

Some derivatives of dipeptides containing a His residue catalyzed the ring opening of 2-phenyl-4-benzyl-5(4H)-oxazolone by methanol. The mixture of cyclo[(S)-His-(S)-Phe] (CHP) with chiral auxiliaries which possess both a hydrogen-bond donor and a hydrogen-bond acceptor was a more effective and enantioselective catalyst than the CHP alone. The influence of racemic and the two enantiomerically pure auxiliaries on the cyclo[(S)-His-(S)-Phe]-catalyzed alcoholysis of the 5(4H)-oxazolone was different. A mixture of CHP with -diisopropyl tartrate catalyzed the enantioselective ring opening of 2-phenyl-4-benzyl-5(4H)-oxazolone by methanol, ethanol and n-butanol, preferentially affording the N-benzoyl- -phenylalaninates (20–39% e.e.).     

Asymmetric synthesis of quinolizidine alkaloids (−)-lasubine I, (−)-lasubine II and (+)-subcosine II

The enantioselective synthesis of (−)-lasubine I 1 and the first asymmetric synthesis of (−)-lasubine II 2 and (+)-subcosine II 3 is described. The key step is the intramolecular cyclization of N-acyliminium ion 4 which is derived from (S)-aminoester 6.     

四氮杂杯[2]芳烃[2]三嗪键合硅胶固相萃取-高效液相色谱法测定河水中硝基苯酚和己烯雌酚

基于四氮杂杯[2]芳烃[2]三嗪键合硅胶吸附剂（NC-Si）,构建了固相萃取-高效液相色谱法同时测定河水中3种硝基苯酚和己烯雌酚的新方法。考察并获得了固相萃取和液相色谱分离的优化条件：将样品溶液pH调至5,以5 mL/min上样,经自制固相萃取柱净化,2 mL氨水-甲醇（2：98,v/v）洗脱;在C8柱上以甲醇-0.1%磷酸溶液为流动相进行梯度洗脱。4种目标分析物的检出限（LOD,S/N=3）为0.03~0.3 μg/L,定量限（LOQ,S/N=10）为0.1~1.0 μg/L;加标回收率为75.5%~104.2%,相对标准偏差（RSD,n=5）小于6.3%。该方法准确、可靠,可用于河水中硝基苯酚及己烯雌酚的灵敏检测。     

Chiral C2-symmetric 2,3-disubstituted aziridine and 2,6-disubstituted piperidine as chiral ligands in the addition reaction of diethylzinc with arylaldehydes

Chiral C₂-symmetric 2,3-disubstituted aziridines and 2,6-disubstituted piperidines having a β-amino alcohol moiety have been successfully synthesized and their catalytic chiral induction properties have been examined in the asymmetric addition reactions of diethylzinc with arylaldehydes in hexane. When N-(2,2-diphenyl-2-hydroxyethyl)-(S,S)-2,3-bis(methoxymethyl)aziridine 11 was used as a catalytic chiral ligand, sec-alcohols having (S)-configuration formed in high yields of 86–92% but low enantiomeric excesses (ee's) of 11–13%. However, when N-(2,2-diphenyl-2-hydroxyethyl)-(R,R)-2,6-disubstituted piperidine derivatives 16 and 20 were used as the chiral ligands under the same reaction conditions, the ee's of the corresponding sec-alcohols were 20–30 and 5–6%, respectively, along with the inversion of absolute configuration. A plausible mechanism for this inversion is proposed.     

Capillary electrophoresis of methylmercury with injection by sample stacking

A procedure for separation and quantitation of methylmercury by capillary electrophoresis using sample stacking as the injection technique is presented. The CE conditions have been optimized in order to separate the methylmercury from the excess cysteine peak and to concentrate large volumes of sample obtaining a low detection limit. Under the proposed operational conditions, the detection limit (S/N = 3) was 12 ng g⁻ and the limit of quantitation (S/N = 10) was 20 ng g⁻¹ with a linear range of 20–100 ng g⁻¹ (as methylmercury in samples). The method was tested using different reference materials with a certified methylmercury content.     

Asymmetric hydrogenations of ketones catalyzed by Ru–achiral phosphine-enantiopure diamine complexes

Five novel ruthenium complexes, RuCl₂(MOTPP)₂[(S,S)-DPEN] [MOTPP = tris(4-methoxyphenyl)phosphine] (1), RuCl₂(TFTPP)₂[(S,S)-DPEN] [TFTPP = tris(4-trifluoromethylphenyl)phosphine] (2), RuCl₂(PPh₃)₂[(S,S)-DPEN] (3), RuCl₂(BDPX)[(S,S)-DPEN] [BDPX = 1,2-bis(diphenylphosphinomethyl)benzene] (4), RuCl₂(BISBI)[(S,S)-DPEN][BISBI = 2,2′-bis((diphenylphosphino)methyl)-1,1′-biphenyl]] (5) were synthesized and used for the hydrogenation of aromatic ketones. The complexes showed high catalytic activities, especially that the catalytic activity of complex 5 containing the diphosphine with large bite angle and complex 1 containing triarylphosphine with electron-donating group were higher than the other three complexes. The enantioselectivities of products were almost not influenced by the electron factors of phosphine.     

Monte Carlo optimization of signal-to-noise ratio for electrothermal atomizers

This work uses Monte Carlo simulation models for Cu and Ag to study the change in the signal-to-noise ratio (S/N) with variations on the electrothermal atomizer length and diameter. A 5 × 5 grid corresponding to different lengths (2.0–4.0 cm) and diameters (0.30–0.70 cm) is filled with S/N data from the simulations. It is assumed that the S/N is shot-noise limited. The dosing hole diameter is held at 1.5 mm in all cases. A double-desorption type mechanism for Ag atomization was tested against experimental profiles and good agreement was achieved. Spherical microdroplets release Ag(g) with a fractional order (2/3) and an activation energy of 238 kJ mol⁻¹. Ag(g) readsorbs as dispersed atoms on the wall upon collision. The secondary desorption is first order and has a lower activation barrier (117 kJ mol⁻¹). The S/N predicted by the Monte Carlo simulation does not strongly depend on the heating rate or the nature of the analyte being determined. The optimum with respect to geometry is broad. The optimum furnace diameter is near 0.50 cm, while the optimum furnace length is at the 4.0-cm limit used in these studies. Most commercial atomizers have diameters close to the optimum but shorter lengths, probably reflecting the pragmatic consideration that the longer tubes require larger power supplies and prolonged heating times which may substantially reduce the useful life of the furnace. Further increases in length may also accentuate atomizer nonisothermality which deters analytical improvement.     

A short, practical synthesis of the ant venom alkaloid, three (3R,5S,8aS)-3-alkyl-5-methylindolizidines

A short, practical and diastereoselective method for preparing the ant venom alkaloid, three (3R,5S,8aS)-3-alkyl-5-methylindolizidines (1–3), has been developed. The stereoselective intramolecular amidomercuration of the N-alkenylurethane 4 followed by oxidative demercuration provides the piperidine alcohol cis-6 as a major product. Thereafter, oxidation of cis-6 followed by the Horner-Emmons elongation of the ring appendages affords the enones 8, 10, and 11, which are stereoselectively converted into 1, 2, and 3, respectively, by catalytic hydrogenation.