Asymmetric total synthesis of (+)-1-deoxy-6-epi-castanospermine

(+)-1-Deoxy-6-epi-castanospermine was asymmetrically synthesized in ten steps from α-furfuryl amine derivative 6 in 2.9% overall yield. The kinetic resolution of α-furfuryl amine derivative 6 and Sharpless AD reaction of 14 were used as key steps.     

Preparation of gamma-siloxyallyltributylstannanes and their use in the synthesis of (+/-)-1-deoxy-6,8a-di-epi-castanospermine

gamma-siloxyallyltributylstannanes were selectively obtained as E or Z isomers from beta-tributylstannylacrolein upon reaction with lithium or magnesium alkylcyanocuprates. The ability of the reagents to give a high syn selectivity when added to iminium salts has been used for the efficient synthesis of (+/-)-1-deoxy-6,8a-di-epi-castanospermine from succinimide. The key step of the synthesis was the allylstannation of the N-allyliminium intermediate followed by ring closing metathesis.     

Concise synthesis of 1-epi-castanospermine

1-epi-Castanospermine (5) was synthesized from readily available 2,3,4,6-tetra-O-benzyl-1-deoxynojirimycin (11) in 9 steps and 21% overall yield, with selective debenzylation, Barbier reaction and reductive amination as the main reaction steps.     

Asymmetric and enantiospecific syntheses of 1-hydroxymethyl pyrrolizidine alkaloids

Isoretronecanol and trachelantamidine (laburnine) are naturally occurring pyrrolizidine alkaloids which display potent biological activity, and as such these compounds have, in recent years, attracted significant interest from the bioorganic and synthetic communities. This review delineates both the asymmetric and enantiospecific syntheses of 1-hydroxymethyl pyrrolizidine alkaloids including isoretronecanol, trachelantamidine (laburnine) and related hydroxylated compounds.     

Asymmetric syntheses of methyl N-Boc-2-deoxy-2-amino-l-erythroside,methyl N-Boc-2-deoxy-2-amino-d-threoside and methyl N-Boc-2,3-dideoxy-3-amino-l-arabinopyranoside

The asymmetric syntheses of methyl N-Boc-2-deoxy-2-amino-l-erythroside and methyl N-Boc-2-deoxy-2-amino-d-threoside have been achieved from sorbic acid, in six and eight steps, and in 35 and 13% overall yield, respectively. Diastereoselective aminohydroxylation of tert-butyl sorbate gives access to two diastereoisomeric α-hydroxy-β-amino-γ,δ-unsaturated esters. Reduction of the ester functionality and ozonolysis of the double bond gives the corresponding aldehyde, which exists exclusively in the ring-closed (furanose) form. An alternative synthesis of methyl N-Boc-2-deoxy-2-amino-l-erythroside was also developed, reliant on aminohydroxylation of an α,β-unsaturated ester bearing an acetal functionality at the γ-position, and this synthesis proceeded in five steps and 54% overall yield from acrolein diethyl acetal. This approach was extended to permit the synthesis of methyl N-Boc-2,3-dideoxy-3-amino-l-arabinopyranoside in six steps and 58% overall yield from ethyl 3,3-diethoxypropanote.     

Asymmetric syntheses of heliannuols B and D

The synthesis of heliannuol D along with the first synthesis of heliannuol B has been achieved using Mitsunobu reaction and ring-closing metathesis as the key steps.     

Asymmetric syntheses of fagomine and its stereoisomers

d-Fagomine (1,2,5-trideoxy-1,5-imino-d-arabino-hexitol), a naturally occurring polyhydroxylated piperidine (iminosugar), and its stereoisomers display important biological activities such as glycosidase inhibition. This review delineates both de novo asymmetric and enantiospecific syntheses of fagomine and its stereoisomers.     

Asymmetric Synthesis of Heptacosane-6,8-Diols Induced by Chiral Sulfoxides

The asymmetric synthesis of (6S,8R)-, (6S,8S)-, (6R,8S)- and (6R,8R)-heptacosane-6,8-diols from (2S)-, (2R)-1-[(R)-p-tolylsulfinyl]-2-heptanols and 1-icosanal is described.     

Asymmetric syntheses with BINOL-based imidoyl azide

Thermal decomposition of 2,4,6-trimethylphenyl and (+)-2′-methoxy-1,1′-binaphthalen-2-yl (4-methylphenylsulfonyl)azidimidocarbonates in the presence of norbornene, methyl acrylate, and camphene was studied. (+)-2′-Methoxy-1,1′-binaphthalen-2-yl (4-methylphenylsulfonyl)azidimidocarbonate reacted with norbornene to give (+)-exo-2′-methoxy-1,1′-binaphthalen-2-yl N-(4-methylphenylsulfonyl)-3-azatricyclo-[3.2.1.0^2,4]octane-3-carboximidoate, while in the reaction with methyl acrylate a mixture of stereoisomeric methyl 1-[(2′-methoxy-1,1′-binaphthalen-2-yloxy)(4-methylphenylsulfonylimino)methyl]aziridine-2-carboxylates was obtained. The reaction of 2,4,6-trimethylphenyl (4-methylphenylsulfonyl)azidimidocarbonate with (−)-camphene involved insertion of intermediate nitrene into the exocyclic double bond with formation of 2,4,6-trimethylphenyl N-(3,3-dimethylbicyclo[2.2.1]heptan-2-ylidenemethyl)-N′-(4-methylphenylsulfonyl)-imidocarbamate as a 3: 1 mixture of E,E and E,Z diastereoisomers in good yield. Published in Russian in Zhurnal Organicheskoi Khimii, 2008, Vol. 44, No. 10, pp. 1495–1500. The text was submitted by the authors in English.     

6-羟基染料木素和6,8-二羟基染料木素的简便合成

以鹰嘴豆芽素A为原料,通过溴代、甲氧基化和去甲基化三步反应合成了6-羟基染料木素（2b）和6,8-二羟基染料木素（3b）,总产率分别为20%和40%,其结构经¹H NMR, ¹³C NMR, HR-MS（ESI）和IR表征。      

Improved synthesis of 6-deoxy-1,2-O-isopropylidene-β-L-talofuranose and 6-deoxy-1,2-O-isopropylidene-β-L-idofuranose

Summary The key step in the preparation of 6-deoxy-1,2-O-isopropylidene--L-talofuranose (7) and 6-deoxy-1,2-O-isopropylidene--L-idofuranose (13) is the selective exchange of the 6-O-mesyl rest of 3-O-acetyl-5,6-O-dimesyl-1,2-O-isopropylidene--D-allofuranose (4) and 3-O-acetyl-5,6-O-dimesyl-1,2-O-isopropylidene--D-glucofuranose (10) by acetate group (potassium acetate/18-crown-6).

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Ein neuartiger und präparativ nützlicher Zugang zu 6-Desoxy-1,2-O-isopropyliden--L-talofuranose und 6-Desoxy-1,2-O-isopropyliden--L-idofuranose

Zusammenfassung Schlüsselschritt bei der Herstellung von 6-Desoxy-1,2-O-isopropyliden--L-talofuranose (7) und 6-Desoxy-1,2-O-isopropyliden--L-idofuranose (13) ist der selektive Austausch der primären Mesyl-Gruppe in 3-O-Acetyl-5,6-O-dimesyl-1,2-O-isopropyliden--D-allofuranose (4) und 3-O-Acetyl-5,6-O-dimesyl-1,2-O-isopropyliden--D-glucofuranose (10) durch den Acetat-Rest in Gegenwart von Kaliumacetat/Kronen-Ether.

     

Asymmetric Reduction of Acetophenones with NaBH4 in the Presence of Mono-6-(1-methyl-3-imidazolium)-6-deoxy-β-cyclodextrin Tosylate

The asymmetric reduction of acetophenone and its derivatives was achieved with sodium borohydride utilizing a novel chiral ionic liquid of β-cylclodextrin (CD), mono-6-(1-methyl-3-imidazolium)-6-deoxy-β-cyclodextrin tosylate (MIM-β-CDOTs). It was found that this chiral β-CD-based ionic liquid could provide higher enantioselectivity for the product alcohols. Moreover, the enantioselectivity of the product alcohols was highly dependent on the structure of prochiral ketones, structure of CD and reduction temperature. An erratum to this article can be found at     

Asymmetric first total syntheses and assignment of absolute configuration of oxazinin-5, oxazinin-6 and preoxazinin-7

Asymmetric first total syntheses of the unprecedented toxins oxazinin-5, oxazinin-6 and preoxazinin-7 have been achieved from a common key intermediate 18, derived from a regiocontrolled Sharpless asymmetric aminohydroxylation and oxa-Michael reaction, which in addition to confirming the structure also established the absolute configuration of the natural products. On the way an expeditious synthesis of a metabolite bursatellin was completed in 8 steps.     

Collision-induced decompositions of metal-cationized methyl-6-deoxy-6-bromo-α-D-glucopyranoside derivatives

Collision-induced decompositions (CIDs) of the [M + H]⁺, [M + Li]⁺, [M + Na]⁺, [M + K]⁺ and [M + Ag]⁺ ions of some methyl-6-deoxy-6-bromo-α-D-glucopyranoside derivatives are discussed. Elimination of MeOH resulting in the glycosidyl cation is the predominant reaction of the [M + H]⁺ ion. This process is completely suppressed during CID of the metal-cationized species, which, surprisingly, show elimination of the added metal in the form of RCOO-metal and metal bromide in the case of the ester derivatives. These reactions appear to be assisted by neighbouring group participation. Because of the proximity of the C(3)-oxygen with C(6), the benzyl ether derivative is characterized by the loss of PhCH₂Br from the [M + metal]⁺ ion.     

Unequivocal syntheses of 6-methyl- and 6-phenylisoxanthopterin

Although 6-methyl- ( 1 ) and 6-phenylisoxanthopterin ( 2 ) have previously been synthesized, the requirement of high purity necessary for immunological testing has necessitated our development of the first reported synthesis of these compounds by unequivocal methods. In the process of so doing four new pyrazines, ethyl 3-amino-5-chloro-6-methyl-2-pyrazinecarboxylate ( 11 ), N,N-dimethyl-N'-(6-chloro-3-cyano-5-phenylpyrazin-2-yl)methanimidamide ( 16 ), 2-amino-3-ethoxycarbonyl-5-phenylpyrazine 1-oxide ( 19 ), and ethyl 3-amino-5-chloro-6-phenyl-2-pyrazinecarboxylate ( 20 ) were synthesized. Four new pteridines, 7-methoxy-6-methyl-2,4-pteridinediamine ( 7 ), 7-methoxy-6-phenyl-2,4-pteridinediamine ( 17 ), 2-amino-7-ethoxy-6-methyl-4(3H)-pteridinone ( 12 ), and 2-amino-7-ethoxy-6-phenyl-4(3H)-pteridinone ( 21 ) have also been synthesized enroute to these isoxanthopterins.