Asymmetric Synthesis of 3-Hydroxyprolines by Photocyclization of N-(2-Benzoylethyl)glycinamides

The chiral N-(2-benzoylethyl)-N-tosylglycinamides 1a-c were prepared from the C₂-symmetric pyrrolidines 5a-c . Irradiation of these ketones 1a-c gave cis-3-hydroxyprolinamides 10-12 in moderate to good yields (Scheme 3). The de of the photocyclizations depended on the size of the substituents in positions C(2) and C(5) of the chiral pyrrolidine auxiliaries. In addition, the de varied with the reaction temperature, allowing the determination of activation-parameter differences. The structure of products 10-12 were established by NMR and X-ray analyses.     

Asymmetric Dihydroxylations of β-Substituted N-(α,β-Enoyl)bornane-10,2-sultams

Pure (E)- or (Z)-enoylsultams 2 were Oxidized with OsO₄/N-Methylmorpholine N-oxide in a stereospecific and highly π-face-selective manner. Acetalization of the resulting 1,2-diols furnished, after purification, the stable, crystalline acetals 6 in >99% d.e. and in 63–74% overall yield from 2 . Reductive or hydrolytic cleavage of 6 gave enantiomerically pure alcohols 8 or carboxylic acids 9 with recovery of the sultan auxiliary 1 .     

Synthesis of 6-Substituted 1-Deazapurine 2′-Deoxyribonucleosides

The synthesis of 6-substituted 1-deazapurine 2′-deoxyribonucleosides is described. Glycosylation of the 1-deazapurine (imidazo[4,5-b]pyridine) anions with the α-D -halogenose 5 gives stereoselectively N⁷- and N⁹- regioisomers. ¹H-NMR NOE and ¹³C-NMR spectroscopy are used for unambiguous assignment of isomers, and ¹⁵N-NMR chemical shifts are correlated with σ_para Hammett constants and point charges.     

Electron impact induced water elimination from hydroxyamides. 1—N-(2′-hydroxyethyl)piperidone-2 and N-3′-hydroxypropyl piperidone-2

The main process of the electron impact induced water elimination of the title compounds takes a reaction course comprising several individual steps. A characteristic neighbouring group participation of the carbonyl function is involved, onto which a hydrogen is transferred in a first rate-determining reaction step. This rearranged hydrogen is finally lost together with the hydroxyl group. The reaction of N-(2′-hydroxyethyl)piperidone follows what seems to be a [1,1] elimination whereas the H₂O elimination from N-(3′-hydroxypropyl)piperidone represents a formal [1,2] elimination.     

3′-(1,2,3-Triazol-1-yl)-2′,3′-dideoxythymidine and 3′-(1,2,3-triazol-1-yl)-2′,3′-dideoxyuridine

Cycloaddition of different acetylenic compounds on the azido function of 3′-azido-2′,3′-dideoxythymidine and 3′-azido-2′,3′-dideoxyuridine afforded products with a 1,2,3-triazol-1-yl substituent in the 3′-position. In contrast with the parent compounds, these triazolyl derivatives had no appreciable activity against human immunodeficiency virus (HIV-1).     

Synthesis of Certain 5-Substituted 2′-Deoxytubercidin Derivatives

The synthesis of the 7-deaza-2′-deoxy-adenine derivatives 7b–3 with chloro, bromo, or methyl substituents at C(5) is described. Glycosylation of the 5-substituted 4-chloropyrrolo[2,3-d]pyrimidines 4b–d with 2-deoxy-3,5-di-O-(4-toluoyl)-α-D -erythro-pentofuranosyl chloride ( 3 ) gave the β-D -nucleosides 5b–d , exclusively. They were deblocked (→ 6b–d ) and converted into the tubercidin derivatives 7b–d .     

Synthesis and Properties of 2′-Deoxy-1′,2′-seco-D-ribosyl (5′ → 3′)oligonucleotides (= 1′,2′-seco-DNA) containing adenine and thymine

Some 2′-deoxy-1′,2′-seco-D-ribosyl (5′→3′)oligonucleotides (= 1′,2′-seco-DNA), differing from natural DNA only by a bond scission between the centers C(1′) and C(2′), were synthesized and studied in order to compare their structure properties and pairing behavior with those of corresponding natural DNA and homo-DNA oligonucleotides (2′,3′-dideoxy-β-D-glucopyranosyl oligonucleotides). Starting from (?)-D-tartaric acid, 2′-deoxy-1′,2′-secoadenosine derivative 9a and 1′,2′-secothymidine ( 9b ) were obtained in pure crystalline form. Using the phosphoramidite variant of the phosphite-triester method, a dinucleotide monophosphate 1′,2′-seco-d(T₂) was synthesized in solution, while oligonucleotides 1′,2′-seco-d[(AT)₆], 1′,2′-seco-d(A₁₀) and 1′,2′-seco-d(T₁₀) were prepared on solid phase with either automated or manual techniques. Results of UV- and CD-spectroscopic as well as gel-electrophoretic studies indicated that neither adenine-thymine base pairing (as observed in natural DNA and homo-DNA), nor the adenine-adenine base pairing (as observed in homo-DNA) was effective in 1′,2′-seco-DNA, Furthermore, hybrid pairing was observed neither between 1′.2′-seco-DNA and natural DNA nor between 1′,2′-seco-DNA and homo-DNA.     

Nucleosides and Nucleotides. Part 13. Synthesis and spectral properties of 1- (3′-O-Phosphoryl-2′-deoxy-β -D-ribofuranosyl)-2(1H)-pyridone-(3′-5′)-1-(2′-deoxy-β-D-ribofuranosyl)-2 (1H)-pyridone

The dinucleoside phosphate Π_dpΠ_d ( 4 ) was synthesized from the monomers 1-(5′-O-monomethoxytrityl - 2′ - deoxy - β - D - ribofuranosyl) - 2 (1 H) - pyridone ((MeOTr) Π_d, 2 ) and 1-(5′-O-phosphoryl-3′-O-acetyl-2′-deoxy-β-D -ribofuranosyl)-(1H)-pyridone (pΠ_d(Ac), 3 ). Its 6.4% hyperchromicity and an analysis of the ¹H-NMR. spectra indicate that the conformation and the base-base interactions in 4 are similar to those in natural pyrimidine dinucleoside phosphates.     

Synthesis and Infrared Absorption Spectra of α-methyl-2′-hydroxy-chalcones: I. α-methyl-2′-hydroxychalcone and its 4-Substituted Derivatives

Six 2′-hydroxychalcone derivatives with a methyl group on the α-position were synthesized. Infrared absorption spectra of these new compounds are discussed taking their corresponding α-hydrogen chalcoes which were also synthesized for comparison. This latter study is also utilized as a proof for the structures of these compounds of a new series.     

Mass spectral rearrangements of N-(4′-arylthio-2′-butynyl) N-(2″-arylthio-2″-propenyl)-p-toluidines,N,N-bis(2′-arylthio-2′-propenyl)-p-toluidines and 1,2-bis(arylthio)acenaphthenes

Under electron impact the title compounds display, in addition to the sequential loss of the arylthio groups, the elimination of a bisaryl disulphide moiety, but they do not eliminate sulphur. The behaviour of the p-toluidine derivatives supports the rearrangement pathway proposed earlier for N,N-bis(4′-arylthio-2′-butynyl)anilines.     

3′-Substituted pyrimidines via alkylation-opening of 2,3′-cyclothymidine

Substituted thymidine derivatives are of interest because of their potential antiviral properties. We demonstrate a general strategy for synthesis of 3′-substituted thymidine derivatives, consisting of activation via N-3 alkylation of 2,3′-cyclothymidine followed by nucleophilic opening at the 3′-position. Examples include demonstration of carbon-carbon bond formation at the 3′-position.     

Synthesis of 3′,5′‐Cyclic Phosphate and Thiophosphate Esters of 2′‐C‐Methyl Ribonucleosides

2′‐C‐Methylnucleosides are known to exhibit antiviral activity against Hepatitis C virus. Since the inhibitory activity depends on their intracellular conversion to 5′‐triphosphates, dosing as appropriately protected 5′‐phosphates or 5′‐phosphorothioates appears attractive. For this purpose, four potential pro‐drugs of 2′‐C‐methylguanosine, i.e., 3′,5′‐cyclic phosphorothioate of 2′‐C‐methylguanosine and 2′‐C,O⁶‐dimethylguanosine, 1 and 2 , respectively, the S‐[(pivaloyloxy)methyl] ester of 2′‐C,O⁶‐dimethylguanosine 3′,5′‐cyclic phosphorothioate and the O‐methyl ester of 2′‐C,O⁶‐dimethylguanosine 3′,5′‐cyclic phosphate, 3 and 4 , respectively, have been prepared.     

Asymmetric Synthesis of (S)-5,5,5,5′,5′,5′,5′-Hexafluoroleucine

(S)-5,5,5,5′,5′,5′-Hexafluoroleucine ((S)- 13 ) of 81 % ee is prepared from hexafluoroacetone ( l ) and ethyl bromopyruvate (= ethyl 2-oxopropanoate) in 7 steps with an overall yield of 18% (Schemes 1 and 2). Key step in this sequence is the highly enantioselective reduction of the carbonyl group in α-keto ester 4 either by bakers' yeast (91 % ee) or by ‘catecholborane’ 6 utilizing an oxazaborolidine catalyst, yielding hydroxy ester (R)- 5 with 99% ee. The absolute configuration was determined by X-ray analysis of the HCl adduct (S,R)- 9b of (2S)-N-[(R)- l-phenylethyl]-5,5,5,5′,5′,5′-hexafluoroleucine ethyl ester.     

高效合成叔丁氧羰基氨基乙醛及其用于N-取代甘氨酸酯的合成

以3-氨基-1,2-丙二醇,甲酸二叔丁酯及其合成的醛和甘氨酸甲（乙）酯为原料,经碱性缩合、高碘酸钾氧化、亲核加成一消去和10%Pd/C催化还原,设计合成了几种标题化合物。该合成路线方便,且处理简单,产率为64%-84%。其结构经^1H NMR和^13C NMR确定。