Electronic spectra of 12-S-CIS conformationally locked retinals

The electronic absorption spectra of the four new 12-$\text{s}$-$\text{cis}$-locked retinals (1a–1d) bearing 7-$\text{trans}$, 11-$\text{trans}$ double bond geometries are described and compared with those of analogous 7-$\text{trans}$, 11-$\text{cis}$-geometries (1e–1h) and parent retinals (2a-h).     

Alkaline hydrolysis of 2-(trifluoromethyl)imidazo[4,5-f] and -[4,5-h]quinolines

2-(Trifluoromethyl)imidazo[4,5-$\text{f}$] and -[4,5-$\text{h}$]quinoline have been prepared from 5(6),acetamido-2-(trifluoromethyl)benzimidazole and 7,8-diaminoquinoline respectively. These (trifluoromethyl)- quinolines like 2-(trifluoromethyl)imidazoles but unlike 2-(trifluoromethyl) benzimidazoles, undergo hydrolysis in dilute sodium hydroxide to give ultimately the corresponding imidazo[4,5-$\text{f}$] and -[4,5-$\text{h}$]- quinoline, respectively.     

13C-NMR spectra of 6-aminohexyl glycosides of O-β-D-galactopyranosyl-2-acetamido-2-deoxy-β-D-glucopyranose

¹³C-NMR spectral data on 6-aminohexyl glycosides of $\text{O}$-β-$\text{D}$-galactopyranosyl-2-acetamido-2-deoxy-β-$\text{D}$-glucopyranose are pr     

Stereospecific total synthesis of 12-(r)- and 12- (s)-forms of 6-trans leukotriene B

Non enzymatic hydration of leukotriene A ($\text{1}$), the biogenetic precursor of leukotriene B ($\text{2}$) affords among other products two diastereomeric 6-$\text{trans}$-isomers of 2, the first stereospecific and efficient syntheses of which are recorded herein.     

Synthesis of β-d-mannopyranosides and regioselective o-alkylation of dibutylstannylene complexes

Alkylation of dibutylstannylene complexes of 3,4,6-tri-$\text{O}$-benzyl-$\text{D}$-mannopyranose, methyl 6-$\text{O}$-trityl-α-$\text{D}$-mannopyranoside and methyl α-$\text{D}$-mannopyranoside gives respectively β-$\text{D}$-mannopyranoside and 3-$\text{O}$-alkyl derivatives with high selectivity.     

Steroidal antifeedants from the dorid nudibranch Aldisasanguineacooperi

Two steroids, 3-oxo-chol-4-ene-24-oic acid ($\text{2}$) andi ts unsaturated analog $\text{4}$ have been isolated from the dorid nudibranch $\text{Aldisa}$$\text{sanguinea}$$\text{cooperi}$, and the acid $\text{2}$ has been shown to have antifeedant properties.     

Stereoselective synthesis of the optically active functionalized 1,3,5-all-anti-triol

The optically active 1,3,5-$\text{all}$-$\text{anti}$-triol $\text{20}$ was synthesized starting from ($\text{S}$)-(-)-malic acid with complete stereoselection, based on the stereoselective reduction of cyclic β-keto acetal and successive transthioacetalization.     

Total synthesis of the disaccharide of bleomycin, 2-0-(α-D-mannopyranosyl)-L-gulopyranose

2-0-(α-$\text{D}$-Mannopyranosyl)-$\text{L}$-gulopyranose, the sugar portion of bleomycin has been synthesized.     

Stereospecific synthesis of cis-2-alkenylcyclopropane carboxylic acids; A total synthesis of (±)-cis-chrysanthemic acid

A stereospecific route to $\text{cis}$-2,2-dimethyl-3-alkenyl-cyclopropanecarboxylic Acids is illustrated by a total synthesis of (±)-$\text{cis}$-Chrysanthemic Acid (11). The key step consists of an alicyclic Claisen rearrangement of $\text{O}$-silyl enolates derived from appropriately substituted ($\text{Z}$)-4-hexen-6-olides [e.g.(9)].     

The unexpected intramolecular C-arylation of 2-0-benzylated cyclic sugar derivatives: a useful 1,2-cis-C-glycosylation reaction

Upon treatment with tin(IV) chloride, perbenzylated glycofuranosyl acetates such as 3 or 6 undergo an unusual, intramolecular α-$\text{C}$-arylation resulting from the internal Friedel-Crafts alkylation of the 2-$\text{O}$-benzyl substituent.     

5-Exo-Trig vs 6-Endo-Trig α-acyliminium ion-olefin cyclisations stereoselective synthesis of 7-(1-formyloxy-pent-1-yl)-1-aza-4-oxa-spiro[4.5]decane-2-ones

The two C₆, C₇$\text{trans}$ substituted title compounds have been synthesized via stereoselective 5-$\text{Exo}$-Trig ringclosures starting from (E)-resp. (Z)-4-nonene-1-yl bromide and 3,5-morpholinedione.     

Synthesis of O-6-alkylated deoxyguanosine nucleosides

A general route for synthesis of 6-$\text{O}$-alkyl-2∝deoxyguanosine nucleosides is described. The key step is conversion of the 6-$\text{O}$-TPS derivative $\text{2}$ to the 6-trimethylamino compound $\text{3}$. The trimethylamino group is readily displaced by alcohols in the presence of DBU. Using this route the 6-$\text{O}$-methyl, ethyl and n-butyl 2∝-deoxyguanosine derivatives $\text{5a-c}$ have been prepared in excellent overall yields.     

Synthesis of N-benzoyl-L-ristosamine

The synthesis of N-benzoyl-$\text{L}$-ristosamine (7) from natural tartaric acid through the intermediacy of the δ-$\text{xylo}$ and γ-$\text{ribo}$ lactones (4) and (6) is reported.     

Synthesis of N-benzoyl L- and D-2,3,6-trideoxy-3-aminoxylo-hexose from non-carbohydrate precursors

The enantiomeric alcohols ($\text{2}$) and ($\text{11}$), obtained from (2$\text{R}$,3$\text{R}$) tartaric acid and, respectively, $\text{L}$-threonine, have been used to construct the C₆, enantiomeric deoxy amino sugar derivatives ($\text{7}$) and ($\text{12}$)     

A stereoselective 3-endo-alkyl-5,6-dehydroisoquinuclidine synthesis.

Cycloaddition of N-carbethoxy-2-alkyl-1,2-dihydropyridines $\text{4}$ with phenylvinylsulfone $\text{5}$ provides adducts $\text{6}$, which upon desulfonylation afford stereoselectively N-carbethoxy-3-$\text{endo}$- alkyl-5,6-dehydroisoquinuclidines $\text{1}$.     

Boat-chair conformational preference of exo, exo-9-oxobicyclo[3.3.1]nonane-2,4-dicarboxylic acid

The ¹H and ¹³C nmr spectra of $\text{exo}$, $\text{exo}$-9-oxobicyclo[3.3.1]nonane-2,4-dicarboxylic acid, 3, in DMSO-d₆ or alkaline D₂O, clearly show that it exists in a $\text{boat}$-$\text{chair}$-conformation with $\text{equatorial}$ carboxyl groups, thus being the first case of $\text{boat}$-$\text{chair}$ preference of a bicyclo[3.3.1] nonan-9-one due to the presence of $\text{exo}$,$\text{exo}$-2,4- substituents.     

Synthesis of both 2,3-erythro- and 2,3-threo- isomers of aplidiasphingosine,a bioactive marine terpenoid

2,3-$\text{threo}$- and 13,14-$\text{erythro}$-Relative configurations were proposed for aplidiasphingosine by synthesizing both its 2,3-erythro- and 2,3-$\text{threo}$- isomers and examining their ¹³c-NMR spectra.     

New highly oxidized fusicoccane diterpenoids from the liverwort plagiochilaacanthophylla subsp. japonica

Four novel fusicoccane diterpenoids, fusicoplagins A, B, C, and D, have been isolated from the liverwort $\text{Plagiochila}$$\text{acanthophylla}$ subsp. $\text{japonica}$ and the structures determined by spectroscopic methods, chemical transformations, and X-ray crystallographic analysis.     

N-Acylated α-aminonitriles and their conversion into 5-aminooxazole, 5(4h)-oxazolone and 4(5h)-imidazolone derivatives

In contrast with the reaction of α-aminonitriles $\text{1}$a, the corresponding $\text{N}$-acylated α-aminonitriles $\text{1}$b-f and oxalyl chloride do not yield pyrazinone derivatives, but 5-aminooxazoles $\text{9}$-$\text{11}$ or 4(5$\text{H}$)-imidazolones $\text{12}$, the latter being converted in some cases into imidazo [2,1-$\text{a}$]isoquinoline-2,5,6(3$\text{H}$)-triones. Reactions of compounds $\text{1}$b-f and ethyl chlorooxoacetate provide evidence for a 5(4$\text{H}$)-iminooxazole intermediate $\text{7}$, which aromatizes to yield 5-aminooxazoles $\text{9}$-$\text{11}$; however, unaromatizable īntermediates of type $\text{7}$ - isolable as 5(4$\text{H}$)y-oxazolones $\text{13}$ after hydrolysis - undergo a catalyzed Dimroth-type rearrangement to give imidazolone derivatives $\text{12}$.     

12-S-CIS conformationally locked retinoids: Thermal and photochemical interconversions leading to new geometric isomers

For 12-$\text{s}$-$\text{cis}$ locked retinal analogues, thermal equilibria are established between 11-$\text{cis}$, 13-$\text{cis}$-1c and 13-$\text{cis}$-2c and between 9-$\text{cis}$, 11-$\text{cis}$, 13-$\text{cis}$-1d and 9-$\text{cis}$, 13-$\text{cis}$-2d; a photoisomerization occurs to transform 2c to $\text{all}$-$\text{trans}$-2a and 2d to 9-$\text{cis}$-2b