Nitroxydes 94 : decomposition thermique d'un radical oxazolidine-oxyle.

Pyrolysis of spiro ((4-t-butyl cyclohexane)-1,2′-(4′,4′-dimethyl oxazolidine-3′ oxyl)) $\text{1}$ leads to spiro ((4-t-butyl cyclohexane)-1,2′-(4′,4′ oxazolidine 3′-hydroxy)) $\text{2}$, 4-t-butyl cyclohexanone and 4-t-butyl cyclohexanoxime. Kinetic studies show that the reaction proceeds through an autocatalytic process.     

Chimie des sucres sans groupements protecteurs : synthese de carbamates,d'urees et de thiourees en position 1 du lactose

The anomeric hydroxyl of lactose was carbamoylated selectively by treating the free sugar with alkylisocyanates, thus without preliminary protection of the other hydroxyls of the lactose molecule. Moreover, the readily available 1-aminolactose and 1-octyl-aminolactose reacted with isocyanates and isothiocyanates to afford selectively $\text{N}$-lactosyl $\text{N′}$-alkylureas and $\text{N}$-lactosyl $\text{N′}$-alkylthioureas, respectively.     

Structure of protoveratrine C,a new alkaloid from provoveratrine

Single-crystal $\text{X}$-ray analysis has established that provoveratrine C, a third tetraester component of proveratrine, is protoverine 3-(2′$\text{S}$,3′$\text{R}$-2′,3′-dihydroxy-2′-methylbutyrate 6,7-diacetate 15-(2′$\text{R}$)-methylbutyrate.     

Substituted cyclononatetraenes and nonafulvenes

Reaction of $\text{cis}$,$\text{cis}$,$\text{cis}$,$\text{cis}$-[9]annulene anion ($\text{1}$) with electrophiles ($\text{2a}$-$\text{d}$) leads to substituted $\text{cis}$,$\text{cis}$,$\text{cis}$,$\text{cis}$-1,3,5,7-cyclononatetraenes ($\text{3a}$-$\text{d}$) which are precursors for the preparation of 10- and 10,10′-donor-substituted nonafulvenes (e.g. $\text{7b′}$$\text{e′}$). The influence of solvent and temperature on the ¹H-nmr spectra of the nonafulvenes $\text{7b′}$-$\text{h′}$ has been investigated.     

Some observations relating to phosphorylation methods in oligonucleotide synthesis

A very convenient procedure for the conversion of ($\text{N}$),O-5′-protected deoxyribonucleosides ($\text{8}$) into the triethylammonium salts of the corresponding 3′-($\text{o}$-chlorophenyl) phosphates ($\text{9}$) is described. Good yields of partially-protected 3′→5′-dinucleoside phosphates ($\text{10}$) are obtained from the latter ($\text{9}$) and 3′-unprotected nucleoside building blocks ($\text{12a}$).     

Structure d'un nouvel heteroside d'isoflavone: le sarothamnoside

The structure of sarothamnoside (genistein 7,4′-di-O-[4-O-β-D-glucopyranosyl-β-D-apiofuranoside]), a new isoflavone glycoside from $\text{Sarothamnus scoparius}$ and $\text{S}$, patens, has been established by spectral analysis, mainly ₁₃C NMR.     

Two chrome derivatives from the brown alga Zonariatournefortii

Two minor lipid components of the brown seaweed $\text{Zonaria}$$\text{tournefortii}$ were characterized as (all Z) - 5′,7′-dihydroxy-2′-nonadeca-4,7,10,13,16-pentenyl-chrome chromone ($\text{3}$) and 5′,7′-dihydroxy-2′-pentadecylchrome ($\text{4}$).     

Novel nucleoside analogues via direct attack of carbon : Nucleophiles on nucleosides containing epoxy-sugars

Direct ring-opening of the epoxide ring in 1-(5′-$\text{O}$-trityl-2′,3′-anhydro-β-D-lyxo-furanosyl) uracil (1) by lithium acetylide or vinylmagnesium bromide/cuprous iodide affords the corresponding 5′-$\text{O}$-trity]-3′-$\text{C}$-substituted-3′-deoxy-$\text{ara}$-uridine species.     

Synthesis of detoxininolactone derivatives and the revised absolute stereochemistry of detoxinine

A stereospecific synthesis of acetyl-$\text{L}$-valyl-detoxininolactone has been performed and the absolute stereochemistry of detoxinine has been revised to (2$\text{S}$, 3$\text{R}$, 1′$\text{S}$)-2-(2′-carboxy-1′-hydroxyethyl)-3-hydroxypyrrolidine.     

Synthesis and properties of 3′-deoxyadenylate trimer dA2′p5′A2′p5′A

The trimeric 3′-deoxyadenylyl-(2′→5′)-3′-deoxyadenylyl-(2′→5′)-3′-deoxyadenosine ($\text{1}$$\text{2}$) was synthesized via the phosphotriester approach starting from cordycepine ($\text{1}$). Various physical data have been determined and compared with those of the ribo-A2′p5′A2′p5′A analog.     

New tetrahydropyrans from a marine sponge

Two new tetrahydropyrans have been isolated from the sponge Haliclona sp. From chemical and spectroscopic evidence they are shown to be (1′$\text{R}$, 2$\text{S}$, 2″$\text{E}$, 5$\text{R}$, 6$\text{R}$)-2-(1′-bromethyl)-2,5-dimethyl-6-(penta-2″,4″-dienyl)-tetrahydropyran and (1′$\text{R}$, 2$\text{S}$, 5$\text{R}$, 6$\text{R}$)-2-(1′-bromoethyl)-2,5-dimethyl-6-(pent-4″-enyl)-tetrahydropyran.     

Nouvelle synthese simple de nucleoside phosphorothiolate

The O,S-dimethylphosphorochloridate $\text{10}$ reacts with 5′-O-monomethoxytritylthymidine $\text{11}$ in pyridine giving nucleoside-3′-thiolophosphodiester $\text{13}$ in high yields; in acetonitrile and in the presence of 1-methylimidazole, this reaction leads to the nucleoside-3′-phosphotriester $\text{14}$ without formation of diester $\text{13}$. From the latter, the Tp and TpT have been prepared.     

Stéréosélectiveté de la condensation aldolique. Réaction du benzaldéhyde et d'énolates carbéniates magnésiens α-chlorés

Alkyl chloracetates III (R′ = H) and phenylchloracetates III (R′ = Ph) condense with PhCHO in the presence of (i-Pr)₂NMgBr giving alkyl-2-chloro-3-hydroxy-3-phenyl propionates (RS, RS) (I) and (RS, SR) (II) in equal ratio ($\text{1}\text{1}$) for III (R′ = H) and in the ratio $\text{65}\text{35}$ for III (R′ = Ph) irrespective of the group R. When the same reaction is performed with alkyl chloropropionates III (R′ = CH₃) the isomer ratio is dependent upon the group R. These results are interpreted by considering a planar (R′ = H or Ph) or pyramidal (R′ = CH₃) geometry of the intermediate enolate-carbeniate.     

Syntheses of gramicidin s analogs containing D-Serine or a dehydroalanine residue,and asymmetric hydrogenation of the dehydroalanine

Gramicidin S (GS) analogs, (D-Ser(Bzl)^4,4′]-GS ($\text{17}$), [D-Ser^4,4′]-GS ($\text{18}$), and [L-Orn(Boc)^2,2′,D-Ser^4,4′]-GS ($\text{19}$) were synthesized and $\text{17}$ showed high antibacterial activity. One residue of D-Ser in $\text{19}$ was converted asymmetrically to D-Ala via α,β-dehydroalanine.     

3-methylthio-1,2-dithiolylium salts : Reaction with 4-hydroxy-6-methyl-2H-pyran-2-one and 4-hydroxycoumarin

The reaction of 4- and 5-aryl-3-methylthio-1,2-dithiolylium iodides with 4-hydroxy-6-methyl-2$\text{H}$-pyran-2-one and 4-hydroxycoumarin has been studied. 4-Substituted salts yielded 3-aryl-7-methyl-2-thioxo-2$\text{H}$,5$\text{H}$-pyrano [3,2-c]pyran-5-ones and 3-aryl-2-thioxo-2H,5H-pyrano[3,2-c]benzo[e]pyran-5-ones, respectively, whereas 5-substituted salts gave rise to 3-(5′-aryl-1′,2′-dithiol-3′-ylidene)-6-methyl-2$\text{H}$-pyran-2,4-diones and 3-(5′-aryl-1′,2′-dithiol-3′-ylidene)-2$\text{H}$-benzo [b]-pyran-2,4-diones.     

Five new steroidal glycosides,pregnedioside-A, -B,and their three monoacetates,from an Okinawan soft coral of Alcyonium sp.

Five new pregnene-type steroidal glycosides, named pregnedioside -a ($\text{1}$), 4′-O-acetyl-pregnedioside-a ($\text{2}$), 3′-O-acetyl-pregnedioside-a ($\text{3}$), pregnedioside-b ($\text{5}$), and 4′-O-acetyl-pregnedioside-b ($\text{6}$), were isolated from an Okinawan soft coral of Alcyonium sp. and their structures were elucidated. These are rare examples of steroidal gylcosides from soft coral.     

Herpetetradione,nouveau lignoide tetramere isole d'Herpetospermum caudigerum wall.

The title compound, a new tetramer of coniferyl alcohol, has been isolated from seeds of $\text{Herpetospermum caudigerum}$ Wall. (Cucurbitaceae). Its structure was elucidated by spectroscopic means as $\text{rel}$-(7′S, 8′S, 7″S, 8″)-4,9,4′,4″,4″′,9″′-hexahydroxy-5,5′5″,5″′-tetramethoxy-7,7″′-dioxo-8.3′, 7′.0.9″,8′.8″,9′.0.7″,3″.8″′ -lignoïd.     

An alternative formation of tricarbonylcyclohexadienylium iron salts by acid-catalysed decarbonylation

The action of concentrated sulphuric acid on ($\text{1}$, R = H or CO₂Me, R′ = H) generates the cation ($\text{2}$, R = H or CO₂Me, R′ = H); the stereoisomer ($\text{5}$, R = H, R′ = H) is unaffected. This is an alternative procedure of some utility for the preparation of some cation salts, notably of ($\text{2}$, R = CO₂Me, R′ = H).     

Nucleosides, 45.-Assignment of glycosylation sites in o-hexopyranosyl-ribonucleosides by 13C-NMR

Evidence is presented that glycosylation of a ribose-OH group in nucleosides results in a significant downfield shift for the appended ¹³C nucleus and smaller upfield displacements for the adjacent carbons, providing an efficient tool for differentiating between 2′-$\text{o}$-, 3′-$\text{o}$- and 5′-$\text{o}$-glycosyl-ribonucleosides. Therewith, the products formed on enzymatic galactosylation of uridine, inosine, and adenosine are unequivocally assigned β(1→3)-glycosidic linkages ($\text{3a}$ – $\text{3c}$).     

A novel deaminative cyclization of aminoglycoside. Synthesis of a kanamycin B variant having 2-oxa-5-azabicyclo[2,2,2]oct-1,5-diene ring

The 3′,5′-diene derivative of kanamycin B ($\text{2}$) was obtained from a 4′-ene derivative of kanamycin B ($\text{1}$) by treatment with trimethyl orthoacetate. Formation of the title compound ($\text{4}$) from $\text{2}$ deaminative cyclization with sodium methoxide followed by treatment with trifluoroacetic acid was described.