Kinetic determination of microquantities of D(−)-arabinose

A kinetic method for the determination of microquantities of d(?)-arabinose is presented. The method is based on the accelerating effect of d(?)-arabinose on the reaction between molybdenum(VI) and hydrogen peroxide in solution containing 50 vol% of acetonitrile. In order to find optimum experimental conditions for the determination of d(?)-arabinose, the kinetics of the reaction between molybdenum(VI) and hydrogen peroxide in the presence, as well as in the absence, of d(?)-arabinose was studied. d(?)-Arabinose was determined photometrically by following the rate of the colored reaction product formation. The concentrations of d(?)-arabinose which were determined ranged from 46 to 135 μg/ml, and the standard deviation was lower than 10%.     

Synthesis and optical properties of polyethylenimine containing L-proline and optically active thymine derivatives

Preparation and optical properties of linear polyethylenimine (PEI) containing L -(?)-N-[(?)-2-(thymin-1-yl) propionyl] prolyl group as grafting pendant, [P-(?)Pro-(?)T], and its related monomer and dimer model compounds are described. Hypochromic effects and circular dichroism of these compounds were compared with those of PEI containing (?)-2-(thymin-1-yl) propionyl group as grafting pendant, [P-(?)T], which has no L -proline ring as a spacing group. P-(?)Pro-(?)T showed no exciton coupling of B_2u π-π^* transition although it showed large hypochromicity in neutral aqueous solution, implying that the stacking of the bases has no screw sense.     

Preparation and Absolute Configuration of (−)-(E)-α-trans-Bergamotenone

The synthesis, absolute configuration, and olfactive evaluation of (?)-(E)-α-trans-bergamotenone (= (?)-(1′S,6′R,E)-5-(2′,6′-dimethylbicyclo[3.1.1]hept-2′-en-6′-yl)pent-3-en-2-one; (?)- 1 ), as well as its homologue (?)- 19 are reperted. The previously arbitrarily attributed absolute configuration of 1 and of (?)-α-trans-bergamotene (= (?)-(1 S,6R)-2,6-dimethyl-6-(4-methylpent-3-enyl)bicyclo[3.1. 1]hept-2-ene; (?)- 2 ), together with those of the structurally related aldehydes (?)- 3a,b and alcohols (?)- 4a,b , have been rigorously assigned.     

Total Syntheses of (−)‐Strictosidine and Related Indole Alkaloid Glycosides

A collective synthesis of glycosylated monoterpenoid indole alkaloids is reported. A highly diastereoselective Pictet–Spengler reaction with α‐cyanotryptamine and secologanin tetraacetate as substrates, followed by a reductive decyanation reaction, was developed for the synthesis of (?)‐strictosidine, which is an important intermediate in biosynthesis. This two‐step chemical method was established as an alternative to the biosynthetically employed strictosidine synthase. Furthermore, after carrying out chemical and computational studies, a transition state for induction of diastereoselectivity in our newly discovered Pictet–Spengler reaction is proposed. Having achieved the first enantioselective total synthesis of (?)‐strictosidine in just 10 steps, subsequent bioinspired transformations resulted in the concise total syntheses of (?)‐strictosamide, (?)‐neonaucleoside A, (?)‐cymoside, and (?)‐3α‐dihydrocadambine.     

Synthesis of [4.3.3]Propellanes by Carbenium‐Ion Rearrangement and Their Olfactory Characterization

Treatment of (+)‐sclareolide ( 1 ) with polyphosphoric acid or Eaton's reagent furnished, besides the anticipated cyclopentenone (?)‐ 12 and its isomer (?)‐ 15 , two diastereoisomeric [4.3.3]propellanes (?)‐ 13 and (?)‐ 14 , which possess interesting woody‐ambery odors. The hydrogenated derivative (?)‐ 17 possessed an even more‐powerful odor reminiscent of natural ambergris tincture. Mechanistic insight into this rearrangement was provided by a by‐product 24 of the reaction of sclareolide ( 1 ) with Eaton's reagent. The carbenium ion rearrangement was then employed in the synthesis of four related [4.3.3]propellanes 40 – 43 , illustrating the utility and scope of this reaction. The olfactory properties of the synthesized [4.3.3]propellanes as well as of the original target structures 10, 33 , and 34 , prepared from (?)‐ 12 and (?)‐ 15 , are discussed. Especially the pronounced ambra odor of (?)‐ 17 vividly contradicts the ‘triaxial rule of amber sensation' and provides new insight into the structural requirements for ambra odorants.     

Reaction of sulphoximides with diazomalonate in the presence of Cu-salt : A new synthesis and stereochemistry of optically active oxosulphonium ylides

Sulphoximides (Ia–Ie) were found to react with dimethyl diazomalonate (DDM) in the presence of a catalytic amount of Cu-salts affording the corresponding oxosulphonium ylides in moderate yields. The reaction did not proceed at all under irradiation of UV light. (?)-Methylphenyloxosulphonium bis(methoxycarbonyl)-methylide ((?)-IIb) was obtained from (+)-(S)-methylphenylsulphoximide ((+)-(S)-Ib) together with (?)-(S)-methyl phenyl sulphoxide ((?)-(S)-IIIb) by this reaction. Hydrolysis of (?)-IIb gave (+)-methylphenyloxosulphonium methoxycarbonylmethylide ((+)-IIf) which was converted to (?)-(S)-IIIb upon treatment with dibenzoylethylene. Stereochemical cycle starting from (+)-(S)-Ib to (?)-(S)-IIIb was established and the absolute configurations of both ylides, (?)-IIb and (+)-IIf were assigned as (R)-configuration. The stereochemical courses, namely from (+)-(S)-Ib or (?)-(S)-IIIb to (?)-(R)-IIb or (+)-(R)-IIf to (?)-(S)-IIIb were determined as retention processes. The optical purities of the oxosulphonium ylides obtained from both reactions, (+)-(S)-Ib→(?)-(R)-IIb and (?)-(S)-IIIb→(?)-(R)-IIb, were almost equal. These results indicate that the mechanism of the reaction of sulphoximides with carbenes (or carbenoids) involves the initial formation of the sulphoxides which react subsequently with carbenes to afford the final products.     

Enantioselective synthesis of orthogonally protected (2R,3R)-(−)-epicatechin derivatives,key intermediates in the de novo chemical synthesis of (−)-epicatechin glucuronides and sulfates

Ten orthogonally protected (?)-epicatechin and 3′- or 4′-O-methyl-(?)-epicatechin derivatives were prepared in a regiospecific and enantioselective manner. For each orthogonally protected (?)-epicatechin derivative, one specific phenolic hydroxyl was protected with a methoxymethyl (MOM) or p-methoxybenyzl (PMB) group and the remainder were protected as benzyl ethers. These uniquely protected (?)-epicatechin derivatives were designed to facilitate the regiospecific installation of a glucuronic acid or sulfate unit onto (?)-epicatechin after selective removal of the MOM or PMB protecting group to provide authentic standards of (?)-epicatechin glucuronides and sulfates.     

Notiz zur Konstitution des Laurepukins. 8. Mitteilung über natürliche und synthetische Isochinolin-Derivate

The alkaloid (?)-laurepukine is shown to possess one of the epimeric N-oxide structures 4 or 5 . Oxidation of (?)-pukateine ( 3 ) by hydrogen peroxide gives (?)-laurepukine and, as a second product, 6-epi-laurepukine.     

Tellurium in organic synthesis: a general approach to buteno- and butanolides

The naturally occurring butanolides (?)-blastmycinolactol, (+)-blastmycinone, (?)-NFX-2, (+)-antimycinone as well as the four stereoisomers of the butenolide Acaterin were prepared in high enantiomeric purity using hydroxy-vinyl tellurides as starting materials.     

Synthese von optisch aktiven,natürlichen Carotinoiden und strukturell verwandten Verbindungen. III. Synthese von (+)-Abscisinsäure, (−)-Xanthoxin, (−)-Loliolid, (−)-Actinidiolid und (−)-Dihydroactinidiolid

Synthesis of optically active natural carotenoids and structurally related compounds. III. Synthesis of (+)-abscisic acid, (?)-xanthoxin, (?)-loliolide, (?)-actinidiolide, and (?)-dihydroactinidiolide The syntheses of (+)-abscisic acid ( 1 ), (?)-xanthoxin ( 2 ), (?)-loliolide ( 3 ), (?)-actinidiolide ( 4 ), and of (?)-dihydroactinidiolide ( 5 ) from one common starting material are reported. The syntheses yield also some enantiomeric or diastereomeric analogues.     

Synthesis of (-)-11 Hydroxy-delta8-6a, 10a-trans-tetrahydrocannabinol

When (?)-Δ⁸-6a, 10a-trans-THC (THC = Tetrahydrocannabinol), in the form of its diacetate, was irradiated in the presence of oxygen and a sensitizer, followed by reduction with NaBH₄, three allylic alcohols were formed: (?)-8α-and (?)-8β-hydroxy-Δ^9,11-THC (proportion 3:1) and (?)-9α-hydroxy-Δ^7,8-THC. Acetylation of the epimeric 8-hydroxy-compounds with Ac₂O/pyridine gave the corresponding diacetates. When (?)-Δ⁸-6a, 10a-trans-THC, in the form of its tetrahydropyranyl derivative, was heated with m-chloroperbenzoic acid, the two epimeric 8,9-epoxides were formed in equal amounts. These compounds, on treatment with butyllithium, afforded (?)-8α- and (?)-8β-hydroxy-Δ^9,11- 6a, 10a-trans-THC-tetrahydropyranylether. After removing the protecting group and treatment with Ac₂O/pyridine the same diacetates, as formed by photooxygenation of (?)-Δ⁸-THC-acetate, were obtained as a 1:1-mixture. On heating these epimeric diacetates to 290° they underwent allylic rearrangement to (?)-11-acetoxy-Δ⁸-THC-acetate. From this (?)-11-hydroxy-Δ⁸-6a, 10a-trans-THC was obtained by treatment with LiAlH₄.     

Control of Metal Arrays Based on Heterometallics Masquerading in Heterochiral Aggregations of Chiral Clothespin‐Shaped Complexes

Heterometal arrays in molecular aggregations were obtained by the spontaneous and ultrasound‐induced gelation of organic liquids containing the chiral, clothespin‐shaped trans‐bis(salicylaldiminato) d₈ transition‐metal complexes 1 . Heterometallic mixtures of complexes 1 a (Pd) and 1 b (Pt) underwent strict heterochiral aggregation entirely due to the organic shell structure of the clothespin shape, with no effect of the metal cores. This phenomenon provides an unprecedented means of generating highly controlled heterometallic arrangements such as alternating sequences [(+)‐Pd(?)‐Pt(+)‐Pd(?)‐Pt ??? ] as well as a variety of single metal‐enriched arrays (e.g., [(+)‐Pt(?)‐Pd(+)‐Pd(?)‐Pd(+)‐Pd(?)‐Pd ??? ] and [(+)‐Pd(?)‐Pt(+)‐Pt(?)‐Pt(+)‐Pt(?)‐Pt ??? ]) upon the introduction of an optically active masquerading unit with a different metal core in the heterochiral single‐metal sequence. The present method can be applied to form various new aggregates with optically active Pd and Pt units, to allow 1) tuning of the gelation ultrasound sensitivity based on the different hearing abilities of the metal units; 2) aggregation‐induced chirality transfer between heterometallic species; and 3) aggregation‐induced chirality enhancement. A mechanistic rationale is proposed for these molecular aggregations based on the molecular structures of the units and the morphologies of the aggregates.     

Synthetic Strategies for (−)‐Cannabidiol and Its Structural Analogs

(?)‐Cannabidiol ((?)‐CBD), a non‐psychoactive phytocannabinoid from Cannabis, and its structural analogs have received growing attention in recent years because of their potential therapeutic benefits, including neuroprotective, anti‐epileptic, anti‐inflammatory, anxiolytic, and anti‐cancer properties. (?)‐CBD and its analogs have been obtained mainly based on extraction from the natural source; however, the conventional extraction‐based methods have some drawbacks, such as poor quality control along with purification difficulty. Chemical‐synthetic strategies for (?)‐CBD could tackle these issues, and, additionally, generate novel (?)‐CBD analogs that exhibit advanced biological activities. This review concisely summarizes the historic and recent milestones in the synthetic strategies for (?)‐CBD and its analogs.     

Controlled release of volatile (?)-menthol in nanoporous silica materials

In this work, a series of nanoporous silica materials have been prepared as adsorbents for volatile (?)-menthol, a molecule widely used in food, pharmacy, and cosmetics. The isothermal release properties of (?)-menthol have been investigated and correlated with the structural parameters of nanoporous absorbents. A rotary evaporation method is used to effectively load (?)-menthol into the nanopores of adsorbents and to prevent the whisker growth during the adsorption. It is demonstrated that the pore size, structure, wall thickness and surface functionality of nanoporous adsorbents are four important parameters to influence the isothermal release of (?)-menthol. By tuning these parameters of nanoporous silica adsorbents, controlled release of (?)-menthol can be achieved. A vesicular silica material with thick wall and hydrophobic functional groups is shown to possess the slowest release performance. Our contribution provides important knowledge for the future applications of nanoporous silica materials in pharmacy and cosmetics.     

Scaleable processes for the synthesis of (−)-β-d-2,6-diaminopurine dioxolane (Amdoxovir,DAPD) and (−)-β-d-2-aminopurine dioxolane (APD)

An efficient and scalable synthesis of (?)-DAPD and (?)-APD has been developed. We discovered that t-butyl cyanoacetate can be used as a new additive for the sugar nucleoside base coupling step en route to DAPD with improved β-selectivity and an isolated yield four-fold greater than the original process scale method. Using this new process, (?)-DAPD has been prepared on greater than 20 g scale. In the synthesis of (?)-APD, a key enzyme-catalyzed hydrolysis reaction afforded the water soluble deprotected α-anomer while leaving the β-anomer completely untouched.     

Instructions to Authors (1991)

The bridged bis(dihydrooxazole) compound (?)- 2 and its silylated derivative (?)- 3 have been synthesised as building blocks for chiral ligands. The complex of (?)- 3 with Cu^II has been obtained, and its crystal structure has been determined. The Cu^II ion is bound to two deprotonated ligands in a twisted tetracoordinated geometry.     

Sesquiterpenoids from Costus Root Oil (Saussurea lappa CLARKE)

Apart from the well-known constituents (+)-β-selinene ( 2 ), (?)-β-elemene ( 4 ), (+)-β-costol ( 7 ), (?)-caryophyllene ( 17 ), and (?)-elemol ( 19 ) the following sesquiterpenoids have been isolated for the first time from costus root oil (Saussurea lappa CLARKE ): (?)-α-selinene ( 1 ), (+)-selina-4, 11-diene ( 3 ), (?)-α-trans-bergamotene ( 5 ), (?)-α-costol ( 6 ), (+)-γ-costol ( 8 ), (?)-elema-1,3,11 (13)-trien-12-ol ( 9 ), (?)-α-costal ( 11 ), (+)-γ-costal ( 12 ), (+)-γ-costal ( 13 ), (?)-elema-1,3,11 (13)-trien-12-al (elemenal, 14 ), (?)-(E)-trans-bergamota-2, 12-dien-14-al ( 15 ), (?)-ar-curcumene ( 16 ), and (?)-caryophyllene oxide ( 18 ). Compounds 6 , 8 , 9 , and 13 are new sesquiterpenoids. IR. and NMR. spectra of 12 sesquiterpenoids are reproduced.     

Enantioselective Biomimetic Total Syntheses of Kuwanons I and J and Brosimones A and B

The first enantioselective total syntheses of prenylflavonoid Diels–Alder natural products (?)‐kuwanon I, (+)‐kuwanon J, (?)‐brosimone A, and (?)‐brosimone B have been accomplished from a common intermediate based on a concise synthetic strategy. Key elements of the synthesis include a biosynthesis‐inspired asymmetric Diels–Alder cycloaddition mediated by a chiral ligand/boron Lewis acid, as well as a process involving regioselective Schenck ene reaction, reduction, and dehydration to realize a biomimetic dehydrogenation for generation of the required diene precursor. Furthermore, a remarkable tandem inter‐/intramolecular asymmetric Diels–Alder cycloaddition process was applied for the synthesis of (?)‐brosimone A.     

Femtosecond evolution of the pyrrole molecule excited in the near part of its UV spectrum

The evolution of the isolated pyrrole molecule has been followed after excitation in the 265-217 nm range by using femtosecond time delayed ionization. The transients collected in the whole excitation range show the vanishing of the ionization signal in the femtosecond time scale, caused by the relaxation along a πσ(?) type state (3s a(1)←π 1a(2)), which is the lowest excited electronic state of the molecule. This surface is dissociative along the NH bond, yielding a 15 ± 3 fs lifetime that reflects the loss of the ionization cross-section induced by the ultrafast wavepacket motion. Although a weak πσ(?) absorption is detected, the state is mainly reached through internal conversion of the higher bright ππ(?) transitions, which occurs with a 19 ± 3 fs lifetime. In addition to its resonant excitation, the intense ππ(?) absorption extending in the 220-190 nm interval is also out-of-resonance populated at energies far to the red from its absorption onset. This coherent adiabatic excitation of the ππ(?) transition should follow the excitation pulse (coherent population return effect), but instead the system relaxes toward the lower πσ(?) surface through a conical intersection during the interaction time, leading to the population of πσ(?) state at wavelengths as long as 265 nm. According to the observed behavior, the time evolution of the system in the full excitation range studied is modeled by a coherent treatment that provides key insights on the photophysical properties of the molecule.     

3,5,6-三-氧-甲基-D-葡萄糖与N-取代甘氨酸乙酯反应中的Amadori重排

Amadori重排是胺(包括氨基酸)与还原糖间一系列复杂反应中的很重要的一步,反应。一级胺以及二级芳香胺与还原糖反应中的Amadori 重排已有大量报道,但对涉及二级脂肪胺特别是 N-取代氨基酸的报道却为数甚少。Anet 曾报道了 N-取代甘氨酸与葡萄糖作用后,得到 Amadori 重排产物的结果,但对其作用机制及反应中间产物无详细描述。本文研究了 N-取代甘氨酸乙酯与3,5,6-三-氧-