Transformation of (+)-thiomicamine into the p-methylthio analogue of (+)-5-epi-cytoxazone

(2S,3S)-(+)-Thiomicamine 3, a commercially available aminodiol, was transformed into (4R,5S)-5-hydroxymethyl-4-(p-methylthiophenyl)-2-oxazolidinone 10, a compound related to cytoxazone-type biologically active natural products. The synthetic strategy of the highly regio- and stereoselective synthesis was based upon the reversal of the position of the hydroxyl and amine functionalities in 3, accomplished via azidolysis of the key intermediate, epoxide 6.     

Stereoselective synthesis of (+)-boronolide and (−)-5-epi-boronolide

Stereoselective synthesis of boronolide and 5-epi-boronolide was achieved from d-(−)-tartaric acid. The key step involves the reduction of a keto Weinreb amide for the synthesis of boronolide, and a single pot construction of a diketone from the bis-Weinreb amide of tartaric acid and subsequent reduction with L-Selectride for 5-epi-boronolide.     

Enantiospecific Synthesis of 5-Methoxy-D(+)- OR L(-) Tryptophan

A method for the enantiospecific synthesis of 5-methoxy-D(+)-tryptophan 8 or the L(-)-optical antipode is described. This procedure can be scaled up and performed without the need for extensive chromatographic separations. It provides for the first time the synthesis of the optically pure 5-methoxy-D(+) or L(-)-tryptophans required for alkaloid total synthesis.     

(+)-(1S,2S,5R)-8-联苯薄荷醇的合成

以(R)-( )-pu legone为起始原料,经1,4-加成,还原两步反应合成了手性辅助试剂( )-(1S,2S,5R)-8-联苯薄荷醇及其差向异构体(-)-(1R,2S,5R)-8-联苯薄荷醇,总产率95%。其结构经1H NMR,13C NMR,IR,MS和X-射线衍射仪表征。     

Total synthesis of (+)-5α-dihydropregnenolone via acetylene-cation cyclization

The stereoselective total synthesis of (+)-5α-dihydropregnenolone $\text{7}$ via acetylene-cation cyclization of $\text{6}$, which was readily prepared from the optically active D-ring aromatic steroid $\text{1}$, is described.     

Enthalpies of formation of gas-phase N3, N3-, N5+, and N5- from Ab initio molecular orbital theory, stability predictions for N5(+)N3(-) and N5(+)N5(-), and experimental evidence for the instability of N5(+)N3(-)

Ab initio molecular orbital theory has been used to calculate accurate enthalpies of formation and adiabatic electron affinities or ionization potentials for N3, N3-, N5+, and N5- from total atomization energies. The calculated heats of formation of the gas-phase molecules/ions at 0 K are DeltaHf(N3(2Pi)) = 109.2, DeltaHf(N3-(1sigma+)) = 47.4, DeltaHf(N5-(1A1')) = 62.3, and DeltaHf(N5+(1A1)) = 353.3 kcal/mol with an estimated error bar of +/-1 kcal/mol. For comparison purposes, the error in the calculated bond energy for N2 is 0.72 kcal/mol. Born-Haber cycle calculations, using estimated lattice energies and the adiabatic ionization potentials of the anions and electron affinities of the cations, enable reliable stability predictions for the hypothetical N5(+)N3(-) and N5(+)N5(-) salts. The calculations show that neither salt can be stabilized and that both should decompose spontaneously into N3 radicals and N2. This conclusion was experimentally confirmed for the N5(+)N3(-) salt by low-temperature metathetical reactions between N5SbF6 and alkali metal azides in different solvents, resulting in violent reactions with spontaneous nitrogen evolution. It is emphasized that one needs to use adiabatic ionization potentials and electron affinities instead of vertical potentials and affinities for salt stability predictions when the formed radicals are not vibrationally stable. This is the case for the N5 radicals where the energy difference between vertical and adiabatic potentials amounts to about 100 kcal/mol per N5.     

Crystal Structure of 5-(l-Menthyloxy)-3-Bromo-4-(R)-(+)-Methylbenzylamino-2(5H)-Furanone

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Synthesis of (+)-(R)-5-hydroxy-6-hydroxymethyl-7-methoxy-8-methylflavanone

The synthesis of (+)-(R)-5-hydroxy-6-hydroxymethyl-7-methoxy-8-methylflavanone is described. A new chromylation method of β-ketosulfoxide 9 leading to the Michael acceptor 12 has been developed. Dilithium tetrachlorocuprate was shown to be a very efficient catalyst for the conjugate addition reaction of phenyl magnesium bromide to the α,β-unsaturated sulfoxide 12. The instability of the obtained adducts 10 represents a limitation in terms of yield. It was confirmed that the natural flavanone leridol does not possess the structure of title compound 1.     

First total syntheses of (+)-7-deoxynogarol and (+)-7-con-o-methylnogarol

The first total syntheses of (+)-7-deoxynogarol (2) and (+)-7-con-O-methylnogarol (3), the notable members of nogalamycin congeners, were achieved employing the Diels-Alder reaction of the highly functionalized dienes (11 and 20) with the (+)-naphthoquinone (6), the CDEF-ring system of nogalamycin congeners, as a key synthetic step.     

(+)-Trans-chrysanthemic acid from (+)-Δ3-carene

A new and more efficient route for the conversion of the readily available (+)-Δ³-carene into (+)-trans-chrysanthemic acid is described.     

Enantioselective synthesis of (+)- and (-)-dihydroepiepoformin and (+)-epiepoformin

[reaction: see text] The enantioselective synthesis of both enantiomers of dihydroepiepoformin (1) and (+)-epiepoformin (2) was achieved from (p-tolylsulfinyl)methyl-p-quinols (SR)- or (SS)-3 and (4R,SR)-4, respectively. Key features include the stereocontrolled conjugate addition of AlMe3 to p-quinol 3 and retrocondensation to the ketone functionality, previous to oxidation of the beta-hydroxy sulfoxide moiety of advanced intermediates to the corresponding sulfone.     

Syntheses of (+)-alismoxide and (+)-4-epi-alismoxide

The first total syntheses of (+)-alismoxide and (+)-4-epi-alismoxide are reported. Formal chemo-, regio-, and stereoselective addition of water to 10alpha-acetoxy-1alphaH,5betaH-guaia-3,6-diene afforded the target compounds after reduction. The absolute stereochemistry of (+)-alismoxide has been established. The low [alpha](D) +8.6 value indicates that significant amounts of alismoxide result from biosynthetic processes. Furthermore, the structure of the natural guaienediol isolated from Silphium perfoliatum has been corrected to (-)-alismoxide.     

Semisynthesis of (+)- and (−)-goniomitine from (−)- and (+)-vincadifformine

The first biomimetic semisynthesis of goniomitine has been accomplished in nine steps with 11% overall yield starting from vincadifformine. Natural (?)- and unnatural (+)-goniomitine were prepared from (+)- and (?)-vincadifformine, respectively. The evaluation of the antiproliferative effect of both enantiomers proved unnatural (+)-goniomitine to be more potent, but this enantiomer as well as some close derivatives displayed a moderate activity only.     

(R)-(＋)-5-甲基-5-{4-[2-(2-(5-氯吲唑基))乙氧基]苄基}-2,4-噁唑烷二酮的合成及其绝对构型的确定

以(S)-(－)-1-苯乙胺为拆分剂对外消旋的α-羟基酸进行拆分, 得到手性α-羟基酯4, 再与尿素合环、脱甲基保护, 得到关键的手性中间体(R)-(＋)-5-甲基-5-(4-羟基苄基)-2,4-噁唑烷二酮(6). 将化合物6与甲磺酸酯(8)缩合即得具有全新化学结构的标题化合物9 (ee值100%), 其结构经1 H NMR和HRMS确证. 根据拆分盐3的单晶X射线衍射分析结果及由α-羟基酯4与尿素合环生成噁唑烷二酮的反应机理, 确定标题化合物9的绝对构型为R.     

Total Syntheses of (+)-Goniotriol and (+)- 8-Acetylgoniotriol

Two styryl-pyrones, (+)-goniotriol (1) and (+)-8-acetylgoniotriol (2), which are cytotoxic to human turnout cells, were isolated from the ethanolic extracts of the stem bark of Goniothalamus giganteus Hook. F., Thomas (Annonaceae), in addition (+)-goniotriol was also isolated from the leaves and twigs of Goniothalamus