A rapid and diverse construction of 6-substituted-5,6-dihydro-4-hydroxy-2-pyrones through double Reformatsky reaction

A rapid and diverse synthesis of biologically important 6-substituted-5,6-dihydro-4-hydroxy-2-pyrones through a double Reformatsky reaction of aldehydes to δ-hydroxy-β-ketoesters followed by lactonization is described. Due to the high functional group tolerance and reaction site discrimination between aldehyde, nitrile, and ester groups in the substrate, the protocol can provide the dihydropyrones with bromo, nitro, carboxylic acid, and β-ketoester groups, which are suitable for the further derivatizations. Furthermore, the protocol has been successfully applied to the rapid total synthesis of naturally occurring Yangonin.     

Synthesis of 1-substituted-6-methyluracils

A series of 6-methyl-1H-pyrimidin-2,4-diones bearing different substituents in the 1-position of the uracil ring were prepared starting from substituted ureas and diketene.     

Modified Coumarins. 6. Synthesis of Substituted 5,6-Benzopsoralens

Substituted 5H-benzo[c]furo[3,2-g]chromen-5-ones, modified analogs of psoralen that contain a benzene ring annelated at the 5,6-position of a furo[3,2-g]chromen-7-one system, were synthesized from 3-hydroxy- 6H-benzo[c]chromen-6-ones.     

Photochemical functionalization of 6-azauracils to 5-substituted-6-azauracils

Photochemical cycloaddition of 6-azauracil derivatives to enol acetates yields hydrolytically labile bicyclic azetidines which decompose in good to excellent yield to 5-substituted-5,6-dihydro-6-azauracils. These compounds can in turn be oxidized by bromine to the 5-substituted-6-azauracil. This reaction sequence has also been applied to 2′,3′,5′-tri-o-benzoyl-6-azauridine resulting in a 60% overall yield of the functionalized nucleoside derivative. The three-step procedure reported here affords a simple method for carbon? carbon bond formation at the 5-position of 6-azauracil and may be applicable to other imines systems.     

An alternate synthesis of 6-substituted-5-deazapteridines

A procedure for synthesis of 2,4-diamino-6-substituted-5-deazapteridines (pyrido[2,3-d]pyrimidines) is described. Condensation of 1-piperidino-1-propene with ethoxymethylenemalononitrile afforded an enamino malononitrile adduct, which when treated with ammonia yielded 2-amino-3-cyano-5-methylpyridine. Cyclization to 2,4-diamino-6-methyl-5-deazapteridine could be effected with guanidine. Similar condensation of piperidinopropene with ethyl methoxymethylenecyanoacetate followed by cyclization with hydroxylamine gave 2-amino-3-carbethoxy-6-methylpyridine 1-oxide. Reduction with phosphorus trichloride afforded the pyridine base, however, attempts to cyclize the amino ester to 2-amino-4-hydroxy-6-methyl-5-deazapteridine were unusccessful.     

New Condensation Products from 5,6-Dihydro-4-hydroxy-6-methyl-2-pyrone

We report the synthesis of new condensation products from 5,6-dihydro-4-hydroxy-6-methyl-2-pyrone, providing evidence for the particular reactivity of the 3 and 4 positions of this compound.     

Convenient synthesis of 1,3-substituted-6-phenylpiperazin-2-ones

The convenient preparation of novel 6-phenylpiperazin-2-ones from simple starting materials via a practical two-step procedure is presented. This methodology involves an initial alkylation of 2-bromoacetophenone with an amino ester followed by a one-pot reductive amination and cyclization step to furnish the desired substituted piperazinones.     

Reaction of ethyl γ-bromo-β-methoxycrotonate with carbonyl compounds. Synthesis of 4-methoxy-6-substituted-5,6-dihydro-2H-pyran-2-ones and 3-substituted 3-pyrazolin-5-ones

Ethyl β-methoxycrotonate I reacts with substituted carbonyl compounds II in benzene to give 4-methoxy-6-substituted-5,6-dihydro-2H-pyran-2-ones III. The reaction of IIIa and j with hydrazine hydrate in ethanol leads to 3-[(1′-thienyl-1-hydroxy)methyl]-5-hydroxy-1H-pyrazole (IVa) and 3-[1′-styryl-1′-hydroxy)methyl]-5-hydroxy-1H-pyrazole (IVj) in good yields. The structure of the products were assigned and confirmed on the basis of their elemental analysis and the electronic absorption, infrared and nmr spectra.     

CRYSTAL STRUCTURE OF 6-ETHOXY-5,6-QIHYDROCHELERYTHRINE

<正> C23H23O5N Mr = 393.44, triclinic,space group P 1, a =7.659(3), b= 10.183(10), c=13.396(2)A,α=92.21(7),β=100.86(2),γ=108.16(7)°,Z=2.The structure was solved by direct methods and refined to a final R factor of 0.055, Rw=0.050). The title compound belongs to the alkaloid of benzoheterophenanthrene, the molecule possesses two conjugation planes which are proped up by N(5)-C(6) bond and the dihedral angle is 12.74(24)°.     

A new approach to 6-deoxy-D-allofuranose- and 6-deoxy-L-talofuranose derivatives from 1,2:5,6-di-O-isopropylidene α-D-glucofuranose

3-O-Acetyl-1,2-O-isopropylidene--D-allofuranose (2 b) was prepared from 1,2:5,6-di-O-isopropylidene--D-allofuranose (1 b). Treatment of2 b with triphenylphosphine-diethyl azodicarboxylate afforded regio- and stereospecifically the 5,6-epoxy--D-allo derivative (3). The other diastereomeric compound, 5,6-epoxy-1,2-O-isopropylidene--L-talofuranose (6) was also prepared stereoselectively from2 b via the intermediates5 a and5 b. The epoxy sugars3 and6 were converted with lithium aluminum hydride to the corresponding 6-deoxy-1,2-O-isopropylidene--D-allofuranose (4 a) and --L-talofuranose (7 a) derivatives. Hydrolysis of4 a and7 a afforded 6-deoxy-D-allose and 6-deoxy-L-talose, respectively. The corresponding 3,5-di-O-acetyl- (4 b and7 b) and the 3,5-O-(tetraisopropyldisiloxane-1,3-diyl) derivatives (4 c and7 c) are also described. Selective removal of the isopropylidene group and subsequent acetylation offers a convenient route to prepare sugar derivatives containing furanose ring, like8 b, as a suitable precursor for nucleoside analogs.Herrn Prof. Dr.K. Komarek mit den besten Wünschen zum 60. Geburtstag gewidmet.     

Identification of Antiprotozoal Compounds from Buxus sempervirens L. by PLS-Prediction

Various nor-triterpene alkaloids of Buxus (B.) sempervirens L. have shown remarkable in vitro activity against the causative agents of tropical malaria and East African sleeping sickness. To identify further antiprotozoal compounds of this plant, 20 different fractions of B. sempervirens L., exhibiting a wide range of in vitro bioactivity, were analyzed by UHPLC/+ESI-QqTOF-MS/MS. The analytical profiles were investigated by partial least squares regression (PLS) for correlations between the intensity of LC/MS signals, bioactivity and cytotoxicity. The resulting models highlighted several compounds as mainly responsible for the antiprotozoal activity and thus, worthwhile for subsequent isolation. These compounds were dereplicated based on their mass spectra in comparison with isolated compounds recently reported by us and with literature data. Moreover, an estimation of the cytotoxicity of the highlighted compounds was derived from an additional PLS model in order to identify plant constituents with strong selectivity. In conclusion, high levels of antitrypanosomal and antiplasmodial activity were predicted for eight and four compounds, respectively. These include three hitherto unknown constituents of B. sempervirens L., presumably new natural products.     

新型3－取代－6－芳偶氮香豆素化合物的合成及结构表征

合成了一系列新型偶氮香豆素化合物，通过^1H NMR,IR,MS和元素分析对其结 构进行了确认，同时用X射线单晶衍射测定了化合物2a的晶体结构，其特殊的双功 能分子键连，偶氮基的顺反异构和苯环与香豆素环平面间的扭转平角，使之可能成 为有效的分子器件材料。     

A general synthetic route to 6,6-substituted-6H-dibenzo[b,d]pyrans from dibenzofuran

The reaction of dibenzofuran 1, lithium pieces (2.2 equiv), and TMEDA (2.2 equiv) in dry ether under reflux led to a solution of the corresponding C,O-dilithiated intermediate 2 which, upon treatment with different ketones or aldehydes (0.8 equiv) at -78 degrees C, afforded, after hydrolysis and dehydration, 6,6-substituted-6H-dibenzo[b,d]pyrans 3 in good yields. The reaction undergoes reductive ring opening and cyclization, and the intermediate diol 4e was isolated.