Asymmetric Hydroformylation of Vinylfurans Catalyzed by {(11bS)‐4‐{[(1R)‐2′‐Phosphino[1,1′‐binaphthalen]‐2‐yl]oxy}dinaphtho[2,1‐d:1′,2′‐f]‐ [1,3,2]dioxaphosphepin}rhodium(I) [RhI{(R,S)‐binaphos}] Derivatives

The asymmetric hydroformylation of 2‐ and 3‐vinylfurans ( 2a and 2b , resp.) was investigated by using [Rh{(R,S)‐binaphos}] complexes as catalysts ((R,S)‐binaphos = (11bS)‐4‐{[1R)‐2′‐phosphino[1,1′‐binaphthalen]‐2‐yl]oxy}dinaphtho[2,1‐d:1′,2′‐f][1,3,2]dioxaphosphepin; 1 ). Hydroformylation of 2 gave isoaldehydes 3 in high regio‐ and enantioselectivities (Scheme 2 and Table). Reduction of the aldehydes 3 with NaBH₄ successfully afforded the corresponding alcohols 5 without loss of enantiomeric purity (Scheme 3).     

Stereoselective Reduction of `Capsanthol‐3′‐ones' (=3,6′‐Dihydroxy‐β,κ‐caroten‐3′‐ones) by Complex Hydrides

The (3R,5′R,6′R)‐ and (3R,5′R,6′S)‐capsanthol‐3′‐one (=3,6′‐dihydroxy‐β,κ‐caroten‐3′‐one; 4 and 5 , resp.) were reduced by different complex metal hydrides containing organic ligands. The ratio of the thus obtained diastereoisomeric (3′S)‐capsanthols 2 and 3 or (3′R)‐capsanthols 6 and 7 , respectively, was investigated. Four complex hydrides showed remarkable stereoselectivity and produced the (3′R,6′S)‐capsanthol ( 6 ) in 80 – 100% (see Table 1). The starting materials and the products were characterized by UV/VIS, CD, ¹H‐ and ¹³C‐NMR, and mass spectra.     

Terpenoids from Two Dicranopteris Species

Two new compounds, (6S,13S)‐6‐{[β‐D ‐glucopyranosyl‐(1→4)‐α‐L ‐rhamnopyranosyl]oxy}cleroda‐3,14‐dien‐13‐ol ( 1 ) and kadsuric acid 3‐methyl ester ( 2 ), together with nine known compounds, (6S,13E)‐6‐{[β‐D ‐glucopyranosyl‐(1→4)‐α‐L ‐rhamnopyranosyl]oxy}cleroda‐3,13‐dien‐15‐ol ( 3 ), (6S,13S)‐6‐[6‐O‐acetyl‐β‐D ‐glucopyranosyl‐(1→4)‐α‐L ‐rhamnopyranosyl]oxy}‐13‐{[α‐L ‐rhamnopyranosyl‐(1→4)‐β‐D ‐fucopyranosyl]oxy}cleroda‐3,14‐diene ( 4 ), (6S,13S)‐6‐{[6‐O‐β‐D ‐glucopyranosyl‐(1→4)‐α‐L ‐rhamnopyranosyl]oxy}‐13‐{[α‐L ‐rhamnopyranosyl‐(1→4)‐β‐D ‐fucopyranosyl]oxy}cleroda‐3,14‐diene ( 5 ), 15‐hydroxydehydroabietic acid ( 6 ), 15‐hydroxylabd‐8(17)‐en‐19‐oic acid ( 7 ), junicedric acid ( 8 ), (4β)‐kaur‐16‐en‐18‐oic acid ( 9 ), (4β)‐16‐hydroxykauran‐18‐oic acid ( 10 ), and (4β,16β)‐16‐hydroxykauran‐18‐oic acid ( 11 ) were isolated from the fronds of Dicranopteris linearis or D. ampla. Their structures were established by extensive 1D‐ and 2D‐NMR spectroscopy. Compounds 1 and 3 – 8 showed no anti‐HIV activities.     

Squadinorlignoside: A Novel 7,9′‐Dinorlignan from the Stems of Annona squamosa

Two new polar lignans, i.e., squadinorlignoside (= 4‐[(1E)‐1‐(hydroxymethyl)‐3‐(4‐hydroxyphenyl)prop‐1‐en‐1‐yl]phenyl β‐D ‐glucopyranoside; 1 ) and (6R,7R,8S)‐7a‐[(β‐D ‐glucopyranosyl)oxy]‐1‐methoxyisolariciresinol ( 2 ) were isolated from the stems of Annona squamosa, together with eight known lignans and five known neolignans (compounds 3 – 15 ; Fig. 1). All of these constituents are reported for the first time from the genus Annona. The structures, absolute configurations, and selected conformational aspects of the new compounds were elucidated spectroscopically. Compound 1 is the first example of a 7,9′‐dinorlignan natural product.     

Tirucallane Triterpenoid Saponins from Munronia delavayi Franch

Four new tirucallane triterpenoid saponins, named munronosides I–IV ( 2 – 5 ), along with three known triterpenoids, sapelin B ( 1 ), melianodiol, and (3β)‐22,23‐epoxytirucall‐7‐ene‐3,24,25‐triol, were isolated from the EtOH extract of the whole plants of Munronia delavayi Franch by chromatographic methods. On the basis of spectroscopic evidences, the structures of 2 – 5 were elucidated as (20S,23R,24S)‐21,25‐epoxy‐29‐{{O‐β‐d‐ glucopyranosyl‐(1→3)‐O‐[α‐l‐ rhamnopyranosyl‐(1→6)]‐β‐d‐ glucopyranosyl}oxy}‐23,24‐dihydroxytirucall‐7‐ene‐3,21‐dione ( 2 ), (3β,20S,23R,24S)‐21,25‐epoxy‐29‐{{O‐β‐d‐ glucopyranosyl‐(1→3)‐O‐[α‐l‐ rhamnopyranosyl‐(1→6)]‐β‐d‐ glucopyranosyl}oxy}‐3,23,24‐trihydroxytirucall‐7‐en‐21‐one ( 3 ), (20S,23R,24S)‐24‐(acetyloxy)‐21,25‐epoxy‐29‐{{O‐β‐d‐ glucopyranosyl‐(1→3)‐O‐[α‐l‐ rhamnopyranosyl‐(1→6)]‐β‐d‐ glucopyranosyl}oxy}‐23‐hydroxytirucall‐7‐ene‐3,21‐dione ( 4 ), and (3β,20S,23R,24S)‐24‐(acetyloxy)‐21,25‐epoxy‐29‐{{O‐β‐d‐ glucopyranosyl‐(1→3)‐O‐[α‐l‐ rhamnopyranosyl‐(1→6)]‐β‐d‐ glucopyranosyl}oxy}‐3,23‐dihydroxytirucall‐7‐en‐21‐one ( 5 ).     

1,3‐Oxathiolanes from the Reaction of Aromatic and Enolized Thioketones with Monosubstituted Oxiranes

The reactions of 4,4′‐dimethoxythiobenzophenone ( 1 ) with (S)‐2‐methyloxirane ((S)‐ 2 ) and (R)‐2‐phenyloxirane ((R)‐ 6 ) in the presence of a Lewis acid such as BF₃?Et₂O, ZnCl₂, or SiO₂ in dry CH₂Cl₂ led to the corresponding 1 : 1 adducts, i.e., 1,3‐oxathiolanes (S)‐ 3 with Me at C(5), and (S)‐ 7 and (R)‐ 8 with Ph at C(4) and C(5), respectively. A 1 : 2 adduct, 1,3,6‐dioxathiocane (4S,8S)‐ 4 and 1,3‐dioxolane (S)‐ 9 , respectively, were formed as minor products (Schemes 3 and 5, Tables 1 and 2). Treatment of the 1 : 1 adduct (S)‐ 3 with (S)‐ 2 and BF₃?Et₂O gave the 1 : 2 adduct (4S,8S)‐ 4 (Scheme 4). In the case of the enolized thioketone 1,3‐diphenylprop‐1‐ene‐2‐thiol ( 10 ) with (S)‐ 2 and (R)‐ 6 in the presence of SiO₂, the enesulfanyl alcohols (1′Z,2S)‐ 11 and (1′E,2S)‐ 11 , and (1′Z,2S)‐ 13 , (1′E,2S)‐ 13 , (1′Z,1R)‐ 15 , and (1′E,1R)‐ 15 , respectively, as well as a 1,3‐oxathiolane (S)‐ 14 were formed (Schemes 6 and 8). In the presence of HCl, the enesulfanyl alcohols (1′Z,2S)‐ 11 , (1′Z,2S)‐ 13 , (1′E,2S)‐ 13 , (1′Z,1R)‐ 15 , and (1′E,1R)‐ 15 cyclize to give the corresponding 1,3‐oxathiolanes (S)‐ 12 , (S)‐ 14 , and (R)‐ 16 , respectively (Schemes 7, 9, and 10). The structures of (1′E,2S)‐ 11 , (S)‐ 12 , and (S)‐ 14 were confirmed by X‐ray crystallography (Figs. 1–3). These results show that 1,3‐oxathiolanes can be prepared directly via the Lewis acid‐catalyzed reactions of oxiranes with non‐enolizable thioketones, and also in two steps with enolized thioketones. The nucleophilic attack of the thiocarbonyl or enesulfanyl S‐atom at the Lewis acid‐complexed oxirane ring proceeds with high regio‐ and stereoselectivity via an S_n 2‐type mechanism.     

Novel Polyoxygenated Spirostanol Glycosides from the Rhizomes of Helleborus orientalis

The two new polyoxygenated spirostanol bisdesmosides 1 and 2 and the new trisdesmoside 3 , named hellebosaponin A ( 1 ), B ( 2 ), and C ( 3 ), respectively, were isolated from the MeOH extract of the rhizomes of Helleborus orientalis. The structures of the new compounds were elucidated as (1β,3β,23S,24S)‐21‐(acetyloxy)‐24‐[(β‐D ‐fucopyranosyl)oxy]‐3,23‐dihydroxyspirosta‐5,25(27)‐dien‐1‐yl O‐β‐D ‐apiofuranosyl‐(1→3)‐O‐(4‐O‐acetyl‐α‐L ‐rhamnopyranosyl)‐(1→2)‐O‐[β‐D ‐xylopyranosyl‐(1→3)]‐α‐L ‐arabinopyranoside ( 1 ), (1β,3β,23S,24S)‐ 21‐(acetyloxy)‐24‐{[O‐β‐D ‐glucopyranosyl‐(1→4)‐β‐D ‐fucopyranosyl]oxy}‐3,23‐dihydroxyspirosta‐5,25(27)‐dien‐1‐yl O‐β‐D ‐apiofuranosyl‐(1→3)‐O‐(4‐O‐acetyl‐α‐L ‐rhamnopyranosyl)‐(1→2)‐O‐[β‐D ‐xylopyranosyl‐(1→3)]‐ α‐L ‐arabinopyranoside ( 2 ), and (1β,3β,23S,24S)‐24‐[(β‐D ‐fucopyranosyl)oxy]‐21‐{[O‐β‐D ‐glucopyranosyl‐(1→2)‐β‐D ‐galactopyranosyl]oxy}‐3,23‐dihydroxyspirosta‐5,25(27)‐dien‐1‐yl O‐β‐D ‐apiofuranosyl‐(1→3)‐O‐(4‐O‐acetyl‐α‐L ‐rhamnopyranosyl)‐(1→2)‐O‐[β‐D ‐xylopyranosyl‐(1→3)]‐α‐L ‐arabinopyranoside ( 3 ), respectively, on the basis of detailed spectroscopic studies and chemical evidence.     

Two New Iridoid Glycosides from Hedyotis tenelliflora Blume

Two new iridoid glycosides, teneoside A (=(2aR,5S)‐5‐[(β‐D ‐glucopyranosyl)oxy]‐2a,4a,5,7b‐tetrahydro‐4‐{[(α‐L ‐rhamnopyranosyl)oxy]methyl}‐1H‐2,6‐dioxacyclopenta[cd]inden‐1‐one; 1 ) and teneoside B (=methyl (1S,5R)‐1‐[(β‐D ‐glucopyranosyl)oxy]‐1,4a,5,7a‐tetrahydro‐5‐hydroxy‐7‐{[(α‐L ‐rhamnopyranosyl)oxy]methyl}cyclopenta[c]pyran‐4‐carboxylate; 2 ), were isolated from the roots of Hedyotis tenelliflora Blume , along with two known compounds, deacetylasperuloside ( 3 ) and scandoside methyl ester ( 4 ). Their structures were elucidated by chemical methods (acid hydrolysis) and spectroscopic analyses.     

Stereoselective Synthesis of 8‐Oxabicyclo[3.2.1]octane‐2,3,4,6,7‐pentols and Total Asymmetric Synthesis of 2,6‐Anhydrohepturonic Acid Derivatives and of β‐C‐manno‐Pyranosides Suitable for the Construction of (1→3)‐C,C‐Linked Trisaccharides

Enantiomerically pure (+)‐(1S,4S,5S,6S)‐6‐endo‐(benzyloxy)‐5‐exo‐{[(tert‐butyl)dimethylsilyl]oxy}‐7‐oxabicyclo[2.2.1]heptan‐2‐one ((+)‐ 5 ) and its enantiomer (−)‐ 5 , obtained readily from the Diels‐Alder addition of furan to 1‐cyanovinyl acetate, can be converted with high stereoselectivity into 8‐oxabicyclo[3.2.1]octane‐2,3,4,6,7‐pentol derivatives (see 23 – 28 in Scheme 2). A precursor of them, (1R,2S,4R,5S,6S,7R,8R)‐7‐endo‐(benzyloxy)‐8‐exo‐hydroxy‐3,9‐dioxatricyclo[4.2.1.0^2,4]non‐5‐endo‐yl benzoate ((−)‐ 19 ), is transformed into (1R,2R,5S, 6S,7R,8S)‐6‐exo,8‐endo‐bis(acetyloxy)‐2‐endo‐(benzyloxy)‐4‐oxo‐3,9‐dioxabicyclo[3.3.1]non‐7‐endo‐yl benzoate ((−)‐ 43 ) (see Scheme 5). The latter is the precursor of several protected 2,6‐anhydrohepturonic acid derivatives such as the diethyl dithioacetal (−)‐ 57 of methyl 3,5‐di‐O‐acetyl‐2,6‐anhydro‐4‐O‐benzoyl‐D ‐glycero‐D ‐galacto‐hepturonate (see Schemes 7 and 8). Hydrolysis of (−)‐ 57 provides methyl 3,5‐di‐O‐acetyl‐2,6‐anhydro‐4‐O‐benzoyl‐D ‐glycero‐D ‐galacto‐hepturonate 48 that undergoes highly diastereoselective Nozaki‐Oshima condensation with the aluminium enolate resulting from the conjugate addition of Me₂AlSPh to (1S,5S,6S,7S)‐7‐endo‐(benzyloxy)‐6‐exo‐{[(tert‐butyl)dimethylsilyl]oxy}‐8‐oxabicyclo[3.2.1]oct‐3‐en‐2‐one ((−)‐ 13 ) derived from (+)‐ 5 (Scheme 12). This generates a β‐C‐mannopyranoside, i.e., methyl (7S)‐3,5‐di‐O‐acetyl‐2,6‐anhydro‐4‐O‐benzoyl‐7‐C‐[(1R,2S,3R,4S,5R,6S,7R)‐6‐endo‐(benzyloxy)‐7‐exo‐{[(tert‐butyl)dimethylsilyl]oxy}‐4‐endo‐hydroxy‐2‐exo‐(phenylthio)‐8‐oxabicyclo[3.2.1]oct‐3‐endo‐yl]‐L ‐glycero‐D ‐manno‐heptonate ((−)‐ 70 ; see Scheme 12), that is converted into the diethyl dithioacetal (−)‐ 75 of methyl 3‐O‐acetyl‐2,6‐anhydro‐4,5‐dideoxy‐4‐C‐{[methyl (7S)‐3,5,7‐tri‐O‐acetyl‐2,6‐anhydro‐4‐O‐benzoyl‐L ‐glycero‐D ‐manno‐heptonate]‐7‐C‐yl}‐5‐C‐(phenylsulfonyl)‐L ‐glycero‐D ‐galacto‐hepturonate ( 76 ; see Scheme 13). Repeating the Nozaki‐Oshima condensation to enone (−)‐ 13 and the aldehyde resulting from hydrolysis of (−)‐ 75 , a (1→3)‐C,C‐linked trisaccharide precursor (−)‐ 77 is obtained.     

3′‐Deoxyribopyranose (4′→2′)‐Oligonucleotide Duplexes (=p‐DNA Duplexes) as Substitutes of RNA Hairpin Structures

By automated synthesis, we prepared hybrid oligonucleotides consisting of covalently linked RNA and p‐DNA sequences (p‐DNA=3′‐deoxyribopyranose (4′→2′)‐oligonucleotides) (see Table 1). The pairing properties of corresponding hybrid duplexes, formed from fully complementary single strands were investigated. An uninterrupted π‐π‐stacking at the p‐DNA/RNA interface and cooperative pairing between the two systems was achieved by connecting them via a 4′‐p‐DNA‐2′→5′‐RNA‐3′ and 5′‐RNA‐2′→4′‐p‐DNA‐2′ phosphodiester linkage, respectively (see Fig. 4). The RNA 2′‐phosphoramidites 9 – 12 , required for the formation of the RNA‐2′→4′‐p‐DNA phosphodiester linkage were synthesized from the corresponding, 3′‐O‐tom‐protected ribonucleosides (tom=[(triisopropylsilyl)oxy]methyl; Scheme 1). Analogues of the flavin mononucleotide (=FMN) binding aptamer 22 and the hammerhead ribozyme 25 were prepared. Each of these analogues consisted of two p‐DNA/RNA hybrid single strands with complementary p‐DNA sequences, designed to substitute stem/loop and stem motifs within the parent compounds. By comparative binding and cleavage studies, it was found that mixing of the two complementary p‐DNA/RNA hybrid sequences resulted in the formation of the fully functional analogues 23 ⋅ 24 and 27 ⋅ 28 of the FMN‐binding aptamer and of the hammerhead ribozyme, respectively.     

Novel Fluoride‐Labile Nucleobase‐Protecting Groups for the Synthesis of 3′(2′)‐O‐Aminoacylated RNA Sequences

With the aim to develop a general approach to a total synthesis of aminoacylated t‐RNAs and analogues, we describe the synthesis of stabilized, aminoacylated RNA fragments, which, upon ligation, could lead to aminoacylated t‐RNA structures. Novel RNA phosphoramidites with fluoride‐labile 2′‐O‐[(triisopropylsilyl)oxy]methyl (=tom) sugar‐protecting and N‐{{2‐[(triisopropylsilyl)oxy]benzyl}oxy}carbonyl (=tboc) base‐protecting groups were prepared (Schemes 4 and 5), as well as a solid support containing an immobilized N⁶‐tboc‐protected adenosine with an orthogonal (photolabile) 2′‐O‐[(S)‐1‐(2‐nitrophenyl)ethoxy]methyl (=(S)‐npeom) group (Scheme 6). From these building blocks, a hexameric oligoribonucleotide was prepared by automated synthesis under standard conditions (Scheme 7). After the detachment from the solid support, the resulting fully protected sequence 34 was aminoacylated with L ‐phenylalanine derivatives carrying photolabile N‐protecting groups (→ 42 and 43 ; Scheme 9). Upon removal of the fluoride‐labile sugar‐ and nucleobase‐protecting groups, the still stabilized, partially with the photolabile group protected precursors 44 and 45 , respectively, of an aminoacylated RNA sequence were obtained (Scheme 9 and Fig. 3). Photolysis of 45 under mild conditions resulted in the efficient formation of the 3′(2′)‐O‐aminoacylated RNA sequence 46 (Fig. 4). Additionally, we carried out model investigations concerning the stability of ester bonds of aminoacylated ribonucleotide derivatives under acidic conditions (Table) and established conditions for the purification and handling of 3′(2′)‐O‐aminoacylated RNA sequences and their stabilized precursors.     

Enzyme-Mediated Preparation of the Single Enantiomers of the Olfactory Active Components of the Woody Odorant Timberol®

Enantiomerically pure (3S)- 3a and - 3b , the olfactory active forms of 1-(2,2,6-trimethylcyclohexyl)hexan- 3-ol, components of the commercial woody odorant Timberol ^®, are obtained by lipase-PS-mediated enantioselective acetylation of the allylic alcohols 6 and 7 and of the saturated alcohol 3 . These materials, as mixtures of diastereoisomers, provided (3R)-configured transformation products. However, whereas in the conversion of 6 and 7 there is no diastereoselection, 3 provided the acetate of (1′S,3R,6′R)- 3c much more rapidly than that of the diastereoisomer (1′R,3R,6′S)- 3d (Scheme 3). Inversion of the configuration at C(3) of the side chain of the olfactory inactive (3R)-materials obtained as acetates in the enzymic treatment of 6 , 7 , and 3 also provided, eventually, the desired olfactory active (3S)-products.     

Seven New Phenolic Glucosides from Viburnum cylindricum

Seven new phenolic glucosides, 2′‐O‐acetylhenryoside ( 1 ), 2′,3′‐di‐O‐acetylhenryoside ( 2 ), 2′,6′‐di‐O‐acetylhenryoside ( 3 ), 2′,3′,6′‐tri‐O‐acetylhenryoside ( 4 ), 2′,3′,4′,6′‐tetra‐O‐acetylhenryoside ( 5 ), 2‐[(2,3‐di‐O‐acetyl‐β‐D ‐glucopyranosyl)oxy]‐6‐hydroxybenzoic acid ( 6 ), and 6‐hydroxy‐2‐[(2,3,4,6‐tetra‐O‐acetyl‐β‐D ‐glucopyranosyl)oxy]benzoic acid ( 7 ), were isolated from the leaves and stems of Viburnum cylindricum, along with 26 known compounds (henryoside=2‐(β‐D ‐glucopyranosyloxy)‐6‐hydroxybenzoic acid [2‐(β‐D ‐glucopyranosyloxy)phenyl]methyl ester). The structures of the new compounds were established on the basis of chemical and spectroscopic evidences.     

Hydrolytic Reaction of Plant Extracts to Generate Molecular Diversity: New Dammarane Glycosides from the Mild Acid Hydrolysate of Root Saponins of Panax notoginseng

Molecular diversity was generated by hydrolyzing the crude root saponins of Panax notoginseng (Burk .) F. H. Chen under mild acidic condition (AcOH/EtOH 1 : 1). From the acid hydrolysate, five new dammarane glycosides, named notoginsenoside T₁ (=(3β,6α,12β,20E,23RS)‐24,25‐epoxy‐6‐[(β‐D ‐glucopyranosyl)oxy]‐dammar‐20(22)‐ene‐3,12,23‐triol; 1 ), notoginsenoside T₂ (=(3β,6α,12β,20E,23RS)‐24,25‐epoxy‐6‐[(β‐D ‐glucopyranosyl)oxy]‐23‐methoxydammar‐20(22)‐ene‐3,12‐diol; 2 ), notoginsenoside T₃ (=(3β,6α,12β,20S)‐6‐[(β‐D ‐glucopyranosyl)oxy]‐20‐ethoxydammar‐24‐ene‐3,12‐diol; 3 ), notoginsenoside T₄ (=(3β,6α,12β,20S,22E,24RS)‐6‐[(β‐D ‐glucopyranosyl)oxy]dammar‐22‐ene‐3,12,20,24,25‐pentol; 4 ), and notoginsenoside T₅ (=(3β,6α,12β, 24E)‐6‐[(β‐D ‐xylopyranosyl‐(1→2)‐β‐D ‐glucopyranosyl)oxy]dammara‐20(21),24‐diene‐3,12‐diol; 5 ), were isolated, together with 15 known dammarane glycosides, and their structures were elucidated on the basis of spectroscopic evidence. Among the known compounds, ginsenosides Rg₃ and Rh₁ were isolated as major constituents, in addition to ginsenosides Rg₅, Rh₄, and a mixture of (20R)‐ and (20S)‐25‐hydroxyginsenoside Rh₁, all of which were obtained from P. notoginseng for the first time.     

Nucleotides. Part LXXVIII

Several N(‐hydroxyalkyl)‐2,4‐dinitroanilines were transformed into their phosphoramidites (see 5 and 6 in Scheme 1) in view of their use as fluorescence quenchers, and modified 2‐aminobenzamides (see 9, 10, 18 , and 19 in Scheme 1) were applied in model reactions as fluorophors to determine the relative fluorescence quantum yields of the 3′‐Aba and 5′‐Dnp‐3′‐Aba conjugates (Aba=aminobenzamide, Dnp=dinitroaniline). Thymidine was alkylated with N‐(2‐chloroethyl)‐2,4‐dinitroaniline ( 24 ) to give 25 which was further modified to the building blocks 27 and 28 (Scheme 3). The 2‐amino group in 29 was transformed by diazotation into the 2‐fluoroinosine derivative 30 used as starting material for several reactions at the pyrimidine nucleus (→ 31, 33 , and 35 ; Scheme 4). The 3′,5′‐di‐O‐acetyl‐2′‐deoxy‐N²‐[(dimethylamino)methylene]guanosine ( 37 ) was alkylated with methyl and ethyl iodide preferentially at N(1) to 43 and 44 , and similarly reacted N‐(2‐chloroethyl)‐2,4‐dinitroaniline ( 24 ) to 38 and the N‐(2‐iodoethyl)‐N‐methyl analog 50 to 53 (Scheme 5). The 2′‐deoxyguanosine derivative 53 was transformed into 3′,5′‐di‐O‐acetyl‐2‐fluoro‐1‐{2‐[(2,4‐dinitrophenyl)methylamino]ethyl}inosine ( 54 ; Scheme 5) which reacted with 2,2′‐[ethane‐1,2‐diylbis(oxy)]bis[ethanamine] to modify the 2‐position with an amino spacer resulting in 56 (Scheme 6). Attachment of the fluorescein moiety 55 at 56 via a urea linkage led to the doubly labeled 2′‐deoxyguanosine derivative 57 (Scheme 6). Dimethoxytritylation to 58 and further reaction to the 3′‐succinate 59 and 3′‐phosphoramidite 60 afforded the common building blocks for the oligonucleotide synthesis (Scheme 6). Similarly, 30 reacted with N‐(2‐aminoethyl)‐2,4‐dinitroaniline ( 61 ) thus attaching the quencher at the 2‐position to yield 62 (Scheme 7). The amino spacer was again attached at the same site via a urea bridge to form 64 . The labeling of 64 with the fluorescein derivative 55 was straigthforward giving 65 . and dimethoxytritylation to 66 and further phosphitylation to 67 followed known procedures (Scheme 7). Several oligo‐2′‐deoxynucleotides containing the doubly labeled 2′‐deoxyguanosines at various positions of the chain were formed in a DNA synthesizer, and their fluorescence properties and the T_ms in comparison to their parent duplexes were measured (Tables 1–5).     

Four New Lignan Glycosides from Osmanthus fragrans Lour. var. aurantiacus Makino

Four new tetrahydrofuranoid lignan glycosides, (7S,8R,7′R,8′S)‐4,9,4′,7′‐tetrahydroxy‐3,3′‐dimethoxy‐7,9′‐epoxylignan 9‐O‐β‐D ‐glucopyranoside ( 2 ), (7R,8S,7′S,8′R)‐4,9,4′,7′‐tetrahydroxy‐3,3′‐dimethoxy‐7,9′‐epoxylignan 9‐O‐β‐D ‐glucopyranoside ( 3 ), (7R,8S,7′R,8′S)‐4,9,4′,9′‐tetrahydroxy‐3,3′‐dimethoxy‐7,7′‐epoxylignan 9‐O‐β‐D ‐glucopyranoside ( 4 ), and rel‐(7R,8S,7′S,8′R)‐4,9,4′,9′‐tetrahydroxy‐3,3′‐dimethoxy‐7,7′‐epoxylignan 9‐O‐β‐D ‐glucopyranoside ( 5 ), and ten known lignan glycosides, 1 and 6 – 14 , were isolated from the leaves of Osmanthus fragrans Lour. var. aurantiacus Makino . Their structures were established on the basis of spectral and chemical studies.     

Preparation and (E/Z)‐Isomerization of the Diastereoisomers of Violaxanthin

Violaxanthin A (=(all‐E,3S,5S,6R,3′S,5′S,6′R)‐5,6 : 5′,6′‐diepoxy‐5,6,5′,6′‐tetrahydro‐β,β‐carotene‐3,3′‐diol =syn,syn‐violaxanthin; 5 ) and violaxanthin B (=(all‐E,3S,5S,6R,3′S,5′R,6′S)‐5,6 : 5′,6′‐diepoxy‐5,6,5′,6′‐tetrahydro‐β,β‐carotene‐3,3′‐diol=syn,anti‐violaxanthin; 6 ) were prepared by epoxidation of zeaxanthin diacetate ( 1 ) with monoperphthalic acid. Violaxanthins 5 and 6 were submitted to thermal isomerization and I₂‐catalyzed photoisomerization. The structure of the main products, i.e., (9Z)‐ 5 , (13Z)‐ 5 , (9Z)‐ 6 , (9′Z)‐ 6 , (13Z)‐ 6 , and (13′Z)‐ 6 , was determined by their UV/VIS, CD, ¹H‐NMR, ¹³C‐NMR, and mass spectra.     

Uncovering stereochemical relations in a compound with a stereogenic N—O axis: methyl 2‐(4‐methyl‐2‐thio­xo‐2,3‐di­hydro­thia­zol‐3‐yl­oxy)­propanoate

The geometry of racemic methyl 2‐(4‐methyl‐2‐thio­xo‐2,3‐di­hydro­thia­zol‐3‐yl­oxy)­propanoate, C₈H₁₁NO₃S₂, (I), is characterized by a distorted heterocyclic five‐membered ring and an enantiomorphic N‐alkoxy substituent, which is inclined at an angle of −68.8° to the thia­zole­thione plane in (M)‐(I). The unit cell consists of a 1:1 ratio of R,P‐ and S,M‐configured mol­ecules of (I). The combination of a P configuration at the N—O axis and an R configuration at the asymmetric propanoate C_β atom on one side, and an S,M configuration on the other side, is considered to originate from steric interactions. The largest substituent at the asymmetric propanoate C_β atom, i.e. the methoxycarbonyl group, resides above the methyl substituent; the medium‐sized propanoate γ‐methyl substituent points in the opposite direction with respect to the N—O bond, whereas the H atom is located above the C=S double bond of the thiazolethione subunit.     

Two Antioxidant Alkaloids from Portulaca oleracea L.

Two alkaloids, oleraceins F and G, were isolated from Portulaca oleracea L., and their structures were determined as methyl (2S)‐6‐[(β‐D ‐glucopyranosyl)oxy]‐2,3‐dihydro‐5‐hydroxy‐1‐[(2E)‐3‐(4‐hydroxy‐3‐methoxyphenyl)prop‐2‐enoyl]‐1H‐indole‐2‐carboxylate and methyl (2S)‐6‐[(β‐D ‐glucopyranosyl)oxy]‐2,3‐dihydro‐5‐hydroxy‐1‐[(2E)‐3‐(4‐hydroxyphenyl)prop‐2‐enoyl]‐1H‐indole‐2‐carboxylate, based on their spectroscopic data. Oleraceins F and G exhibited scavenging activity against 1,1‐diphenyl‐2‐picrylhydrazyl (DPPH) radical, with EC₅₀ values of 21.00 and 37.69 μM , respectively.     

Five Aromatics Bearing a 4‐O‐Methylglucose Unit from Cordyceps cicadae

Five new aromatics bearing a 4‐O‐methylglucose unit, namely 3‐methoxy‐1,4‐hydroquinone 1‐(4′‐O‐methyl‐β‐glucopyranoside) (=4‐hydroxy‐3‐methoxyphenyl 4‐O‐methyl‐β‐glucopyranoside; 1 ), 3‐methoxy‐1,4‐hydroquinone 4‐(4′‐O‐methyl‐β‐glucopyranoside) (=4‐hydroxy‐2‐methoxyphenyl 4‐O‐methyl‐β‐glucopyranoside; 2 ), vanillic acid 4‐(4′‐O‐methyl‐β‐glucopyranoside) (=3‐methoxy‐4‐[(O‐methyl‐β‐glucopyranosyl)oxy]benzoic acid; 3 ), 5‐methoxycinnamic acid 3‐O‐(4′‐O‐methyl‐β‐glucopyranoside) (=(2E)‐3‐{3‐methoxy‐5‐[(4‐O‐methyl‐β‐glucopyranosyl)oxy]phenyl}prop‐2‐enoic acid; 4 ), and naphthalene‐1,8‐diol 1,8‐bis(4′‐O‐methyl‐β‐glucopyranoside) (=naphthalene‐1,8‐diyl bis(4‐O‐methyl‐β‐glucopyranoside; 5 ), were isolated from the cultivated Cordyceps cicadae mycelia, together with thirteen known compounds. Their structures were determined by spectroscopic methods. The absolute configurations of the sugar units were not determined.