Synthesis of spiro-cyclopropane derivatives containing multiple chiral centers

Tandem asymmetric double Michael addition/internal nucleophilic substitution of the novel chiral source, 5-(l-menthyloxy)-3-bromo-2(5H)-furanone with nucleophilic alcohol compounds has been investigated. The tandem asymmetric reaction can afford four new stereogenic centers with one reaction and give optically pure spiro-cyclopropane derivatives 5a--5d which are difficult to obtain by routine methods. The synthetic method for 5a--5d was studied in detail and the new compounds were identified on the basis of their analytical data and spectroscopic data, such as [α]~(20),IR,~1H NMR,~(13)C NMR, MS and elementary analysis. The absolute configuration of the sprio [5-l-menthyloxy-3-bromo butyrolactocyclopropane-3″, 3′(4′-methyloxy-5′-menthyloxybutyrolactone)] (5a) was established by X-ray crystallography. The work can provide important synthetic strategy in synthesis of some new optically active spiro-cyclopropane analogues and some biologically active molecules with complex structure.     

光学活性螺-环丙烷双内酯化合物的合成

描述了5-(l-孟氧基)-3-溴-2(5H)-呋喃酮新手性试剂1与氮亲核试剂发生的串联不对称双Michael加成/分子内亲核取代反应,一举生成4个新手性中心。报道了含有叔胺官能团的螺-环丙烷双内酯化合物4a-4d的合成方法以及结构测定。     

Synthesis of enantiomerically pure 3-aminochroman derivatives

Enantiomerically pure (3R)-amino-5-methoxy-3,4-dihydro-2H-1-benzopyran was successfully synthesised in nine steps starting from l-serine. The same synthetic pathway was used to prepare the (3S)-aminochroman derivative starting from d-serine. The enantiomeric purity of the final aminochroman derivatives was determined by capillary electrophoresis using β-cyclodextrin as the chiral selector.     

A valuable synthetic route to spiro-cyclopropane derivatives containing multiple stereogenic centers

The unusual, functionalized spiro-cyclopropane derivatives containing four stereogenic centers 8a–8f were obtained in good yields with d.e. ≥98% via tandem double Michael addition/internal nucleophilic substitution of the novel chiral synthon, 5-l-menthyloxy-3-bromo-2(5H)-furanone 5a, with various oxygen nucleophiles under mild conditions. (S)-(−)-Ethyl lactate also reacted under the same conditions to afford the corresponding spiro-cyclopropane derivative 8g. Interestingly, reaction of 5a with ethyl bromo- and chloroacetate, in the usual manner, gave the spiro-cyclopropane 8h rather than the expected C-linked derivative. The absolute configuration of the interesting spiro-cyclopropanes 8 was established by X-ray crystallography. These results provide a valuable synthetic route to some complex molecules containing the spiro-cyclopropane skeleton with multiple stereogenic centers.     

Synthesis of enantiomerically pure glycerol derivatives containing an organochalcogen unit: In vitro and in vivo antioxidant activity

We describe here the synthesis of enantiomerically pure chalcogenoethers obtained through the reaction of nucleophilic species of chalcogen (S, Se and Te), generated in situ from the respective diorganyl dichalcogenides, with (R)- and (S)-tosyl solketal. Furthermore, some of the chalcogenoethers were treated with acidic cation exchange resin Dowex-(H⁺) leading to the respective deprotected enantiomerically pure 3-phenylchalcogenyl-1,2-diols. In order to explore the biological potential of these molecules, the antioxidant activity of some organochalcogens was evaluated by several in vitro assays. Overall, the chalcogenoethers containing Te were better scavengers of DPPH and ABTS⁺ radicals, had higher ferric reducing capacity and prevented lipid peroxidation. To analyze the effects of these compounds in vivo, we used the alternative model Caenorhabditis elegans. Chalcogenoethers treatment, especially (S)- and (R)-2,2-dimethyl-4-(phenylselanylmethyl)-1,3-dioxolane, conferred protection against the mortality-induced by hydrogen peroxide. Accordingly, these chalcogenoethers were able to modulate the antioxidant enzyme catalase. Notably, the compounds did not present toxicity in worm’s reproduction. To sum up, our study demonstrated that Te- containing chalcogenoethers were promising in vitro scavengers, while Se molecules were more prone to protect against a stressor in vivo. In this sense, the antioxidant activity of chalcogenoethers, especially with Se and Te, indicates that these molecules may have biological application in an attempt to reduce the oxidative stress.     

氨基醇砌块用于螺/环丙环类手性化合物的合成

手性氨基醇砌块3与5-(l-孟氧基)-3-溴-2(5H)-呋喃酮手性合成子4通过串联的不对称双Michael加成/分子内亲核取代反应,得到了具有四个新的手性中心的氨基醇手性砌块/螺环/环丙烷类化合物7(44%～57%,de≥98%)。通过元素分析,[α]^20~D,UV,IR,^1HNMR,^13CNMR,MS确认了它们的化学结构。本工作可以为含有某些活性官能团的多手性中心的复杂结构化合物提供新的合成策略。     

手性螺-环丙烷双内酯化合物的合成与结构

本文进一步研究了5-(l-孟氧基)-3-溴-2(5H)-呋喃酮(1)与氧的亲核试剂,如二苯甲醇、苯甲醇、α-甲基苯甲醇、薄荷醇、冰片醇发生新颖的串联不对称双Michael加成/分子内亲核取代反应,合成了一般方法难以合成的含有多个手性中心的螺[1-溴-4-l-孟氧基-5-氧杂-6-氧代双环[3.1.0]己烷-2,3'-(4'-亲核基-5'-孟氧基丁内酯)](4a-4e)。通过元素分析,IR,UV,^1HNMR,^1^3CNMR,MS,[α]~D^2^0波谱分析数据以及X四圆衍射确定了4a-4e的化学结构和绝对构型。     

Synthesis of enantiomerically pure vinylcyclopropylboronic esters via cross-metathesis

The potent antibiotic ambruticin caused us to investigate two new aspects of cyclopropylboronic ester chemistry: we established the analytical basics for all 1,2,3-trisubstituted diastereoisomers as well as the cross-metathesis as a tool to synthesise vinylcyclopropylboronic esters.     

Synthesis of novel enantiomerically pure tetra-carbohydrazide cyclophane macrocycles

A total of twelve novel enantiomerically pure tetra-carbohydrazide cyclophane macrocycles have been synthesised in quantitative yields by reacting chiral (4R,5R)- and (4S,5S)-1,3-dioxolane-4,5-dicarbohydrazides with aromatic bis-aldehydes in a [2 + 2]-cyclocondensation reaction. The compounds show a dynamic behaviour in solution, which has been rationalized in terms of an unprecedented conformational interconversion between two conformers one stabilised by intramolecular hydrogen bonding and π-π stacking interactions.     

Synthesis of 1-deoxy-D-galactohomonojirimycin via enantiomerically pure allenylstannanes

1-Deoxy-D-galactohomonojirimycin was synthesized in seven steps from optically pure allenylstannane 4 and L-lactate-derived aldehyde 5 in 48% overall yield. The key step was the Lewis acid catalyzed reaction of 4 and 5 to give the syn-amino alcohol in excellent yield and very high diastereoselectivity.     

Efficient synthesis of enantiomerically pure alpha-alkyl cyclopropanecarbonitrile derivatives from pyrazolines

[reaction: see text] Thermolysis of enantiopure sulfonyl pyrazolines 4 and 5, easily obtained from (Z)-3-p-tolylsulfinylacrylonitriles (1), afforded sulfonyl cyclopropanes (6, 7) in a completely stereoselective manner in almost quantitative yields. Both cyclopropanes and alkylidenecyclopropanes, containing one or two chiral carbon atoms, one of them being quaternary, were obtained by hydrogenolysis of the C-S bonding and under the conditions reported by Julia, respectively. The highly stereoselective extrusion of nitrogen suggests a concerted mechanism.     

The synthesis of enantiomerically pure [2.2]paracyclophane derivatives

[2.2]Paracyclophane is a fascinating molecule that offers great potential in a wide range of chemical disciplines. Currently, the synthesis of the majority of enantiomerically pure [2.2]paracyclophane derivatives is based on the resolution of a small number of starting materials or individual resolution procedures are developed for each new compound. The development of more general routes to these valuable compounds via the resolution of a common intermediate is discussed. Ultimately, it would be preferable to synthesise these valuable compounds without recourse to resolution and ideas for this rewarding goal are postulated.     

Synthesis of enantiomerically pure hydroxylated pyrroline N-oxides from d-ribose

A convenient way to obtain enantiomerically pure hydroxylated pyrroline N-oxides is reported. The key step is the formation of ω-oxo enoates from d-ribose and a subsequent 1,3-azaprotio cyclotransfer reaction of the resulting oximino alkenoate derivatives. The stereochemistry of the nitrones obtained is discussed in relation to that of the starting compounds.     

Synthesis of highly oxygenated enantiomerically pure cis-bicyclo[4.3.0]nonanes from secondary sugar allyltin derivatives

Secondary sugar allyltin derivatives of the d-series: Sug-CH(SnBu₃)-CHCH₂ (obtained in an S_N2′ reaction of the corresponding primary allylic mesylates with ‘Bu₃SnCu’) with the S-configuration at the stereogenic center bearing the -SnBu₃ group decompose at 140°C to dienoaldehydes: CH₂CH-CHCH-[(CHOR)₃]-CHO with the cis geometry across the internal double bond. Such aldehydes react with the stabilized Wittig reagents to afford trienes, cyclization of which provides highly oxygenated enantiomerically pure cis-bicyclo[4.3.0]nonenes. This methodology is complementary to that recently proposed by us leading to such bicyclic systems, but with the trans junction between the five- and six-membered rings.     

Synthesis of enantiomerically pure macrolides with hydrazide fragments from tetrahydropyran and l-(+)-tartaric acid derivatives

A synthesis of two potentially useful bicyclic 26- and 33-membered macrolides containing 1,3-dioxolane and hydrazide fragments was developed starting from tetrahydropyran via a [1+1]-condensation of 7′-oxooctyl-7-oxooctanoate and bis(7-oxooctyl)hexanedioate with hydrazide of L-(+)-tartaric acid acetonide derivative.     

Asymmetric synthesis of β-hydroxyacetamides mediated by enantiomerically pure sulphinyl derivatives

The aldol-type condensation of enantiomerically pure α-sulphinylacetamides is described. The stereochemical outcome of the reaction mainly depends on the nature of the base used to generate the enolate. Experimental evidences allow the identification of preferred reaction paths.     

Synthesis of enantiomerically pure cis- and trans-cyclopentane analogues of phenylalanine

For the first time, all stereoisomers of 1-amino-2-phenylcyclopentanecarboxylic acid—c₅Phe—have been synthesised. A Strecker reaction on 2-phenylcyclopentanone and further transformations of each amino nitrile into the amino acid provides cis-c₅Phe and trans-c₅Phe with high efficiency. A divergent synthetic route was then developed to obtain the target compounds cis- and trans-c₅Phe in their racemic form. The preparation of the final enantiomerically pure amino acids and their corresponding N-protected derivatives was also achieved by HPLC resolution of one of the intermediates using a cellulose-derived chiral stationary phase. The relative stereochemistry of each amino acid and its precursors have been unambiguously assigned.