2′,3′‐Dehydrosalannol

The title compound, methyl (2aS,3R,5R,5aS,6S,6aS,8R,9aS,10aR,10bR,10cS)‐8‐(3‐furyl)‐2a,4,5,5a,6,6a,8,9,9a,10a,10b,10c‐dodeca­hydro‐3‐hydroxy‐2a,5a,6a,7‐tetra­methyl‐5‐(3‐methylbut‐2‐enoyl­oxy)‐2H,3H‐cyclo­penta­[4′,5′]­furo­[2′,3′:6,5]benzo[cd]­isobenzo­furan‐6‐acetate, C₃₂H₄₂O₈, was isolated from uncrushed green leaves of Azadirachta indica A. Juss (neem) and has been found to possess antifeedant activity against Spodptera litura. The conformations of the functional groups are similar to those of 3‐des­acetyl­salannin, which was isolated from neem kernels. The mol­ecules are linked into chains by intermolecular O—H?O hydrogen bonds.     

Synthese von diastereo- und enantio-selektiv deuterierten β,ε-, β,β-, β,γ- und γ,γ-Carotinen

Synthesis of Diastereo- and Enantioselectively Deuterated β,ε-, β,β-, β,γ- and γ,γ-Carotenes We describe the synthesis of (1′R, 6′S)-[16′, 16′, 16′-²H₃]-β, εcarotene, (1R, 1′R)-[16, 16, 16, 16′, 16′, 16′-²H₆]-β, β-carotene, (1′R, 6′S)-[16′, 16′, 16′-²H₃]-γ, γ-carotene and (1R, 1′R, 6S, 6′S)-[16, 16, 16, 16′, 16′, 16′-²H₆]-γ, γ-carotene by a multistep degradation of (4R, 5S, 10S)-[18, 18, 18-²H₃]-didehydroabietane to optically active deuterated β-, ε- and γ-C₁₁-endgroups and subsequent building up according to schemes \documentclass{article}\pagestyle{empty}\begin{document}${\rm C}_{11} \to {\rm C}_{14}^{C_{\mathop {26}\limits_ \to }} \to {\rm C}_{40} $\end{document} and C₁₁ → C₁₄; C₁₄+C₁₂+C₁₄→C₄₀. NMR.- and chiroptical data allow the identification of the geminal methyl groups in all these compounds. The optical activity of all-(E)-[²H₆]-β,β-carotene, which is solely due to the isotopically different substituent not directly attached to the chiral centres, is demonstrated by a significant CD.-effect at low temperature. Therefore, if an enzymatic cyclization of [17, 17, 17, 17′, 17′, 17′-²H₆]lycopine can be achieved, the steric course of the cyclization step would be derivable from NMR.- and CD.-spectra with very small samples of the isolated cyclic carotenes. A general scheme for the possible course of the cyclization steps is presented.     

Three ginkgolide hydrates from Ginkgo biloba L.: ginkgolide A monohydrate,ginkgolide C sesquihydrate and ginkgolide J dihydrate,all determined at 120 K

A low‐temperature structure of ginkgolide A monohydrate, (1R,3S,3aS,4R,6aR,7aR,7bR,8S,10aS,11aS)‐3‐(1,1‐dimethylethyl)‐hexa­hydro‐4,7b‐di­hydroxy‐8‐methyl‐9H‐1,7a‐epoxymethano‐1H,6aH‐cyclo­penta­[c]­furo­[2,3‐b]­furo­[3′,2′:3,4]­cyclopenta­[1,2‐d]­furan‐5,9,12(4H)‐trione monohydrate, C₂₀H₂₄O₉·H₂O, obtained from Mo Kα data, is a factor of three more precise than the previous room‐temperature determination. A refinement of the ginkgolide A monohydrate structure with Cu Kα data has allowed the assignment of the absolute configuration of the series of compounds. Ginkgolide C sesquihydrate, (1S,2R,3S,3aS,4R,6aR,7aR,7bR,8S,10aS,11S,11aR)‐3‐(1,1‐di­methyl­ethyl)‐hexa­hydro‐2,4,7b,11‐tetrahydroxy‐8‐methyl‐9H‐1,7a‐epoxy­methano‐1H,6aH‐cyclopenta­[c]­furo­[2,3‐b]­furo­[3′,2′:3,4]­cyclo­penta­[1,2‐d]­furan‐5,9,12(4H)‐trione sesquihydrate, C₂₀H₂₄O₁₁·1.5H₂O, has two independent diterpene mol­ecules, both of which exhibit intramolecular hydrogen bonding between OH groups. Ginkgolide J dihydrate, (1S,2R,3S,3aS,4R,6aR,7aR,7bR,8S,10aS,11aS)‐3‐(1,1‐di­methyl­ethyl)‐hexa­hydro‐2,4,7b‐tri­hydroxy‐8‐methyl‐9H‐1,7a‐epoxy­methano‐1H,6aH‐cyclo­penta­[c]­furo­[2,3‐b]furo[3′,2′:3,4]­cyclo­penta­[1,2‐d]­furan‐5,9,12(4H)‐trione dihydrate, C₂₀H₂₄O₁₀·2H₂O, has the same basic skeleton as the other ginkgolides, with its three OH groups having the same configurations as those in ginkgolide C. The conformations of the six five‐membered rings are quite similar across ­ginkgolides A–C and J, except for the A and F rings of ginkgolide A.     

Two (+)‐α,4‐dimethyl‐2‐oxocyclo­hexaneacetic acids: hydrogen bonding in a terpenoid γ‐keto acid and in a diastereomeric lactol

The (+)‐(αS,1S,4R)‐diastereomer of the title structure, C₁₀H₁₆O₃, aggregates in the solid as non‐symmetric dimers with disorder in both carboxyl groups [O·O = 2.710 (5) and 2.638 (5) Å]. The two mol­ecules constituting the asymmetric unit pair around a pseudo‐twofold rotational axis and differ only slightly in their distances and angles, but one methyl group displays rotational disorder absent in the other mol­ecule. Five inter­molecular C—H·O close contacts exist, involving both ketone groups. The (+)‐(αR,1R,4R)‐diastereomer exists in the crystal in its closed‐ring lactol form, (3R,3aR,6R,7aR)‐2,3,3a,4,5,6,7,7a‐octa­hydro‐7a‐hydroxy‐3,6‐dimethyl­benzo[b]furan‐2‐one, C₁₀H₁₆O₃, and aggregates as hydrogen‐bonded catemers that extend from the hydroxyl group of one mol­ecule to the carbonyl group of a neighbor screw‐related along b [O·O = 2.830 (3) Å and O—H·O = 169°]. One close inter­molecular C—H·O contact exists involving the carbonyl group.     

tert‐Butyl (6S)‐4‐hydroxy‐6‐isobutyl‐2‐oxo‐1,2,5,6‐tetra­hydropyridine‐1‐carboxyl­ate and tert‐butyl (4R,6S)‐4‐hydroxy‐6‐iso­butyl‐2‐oxopiperidine‐1‐carboxyl­ate

X‐ray studies reveal that tert‐butyl (6S)‐6‐iso­butyl‐2,4‐dioxo­piperidine‐1‐carboxyl­ate occurs in the 4‐enol form, viz. tert‐butyl (6S)‐4‐hydroxy‐6‐iso­butyl‐2‐oxo‐1,2,5,6‐tetra­hydropyri­dine‐1‐carboxyl­ate, C₁₄H₂₃NO₄, when crystals are grown from a mixture of di­chloro­methane and pentane, and has an axial orientation of the iso­butyl side chain at the 6‐position of the piperidine ring. Reduction of the keto functionality leads predominantly to the corresponding β‐hydroxy­lated δ‐lactam, tert‐butyl (4R,6S)‐4‐hydroxy‐6‐iso­butyl‐2‐oxo­piperidine‐1‐car­boxyl­ate, C₁₄H₂₅NO₄, with a cis configuration of the 4‐hydroxy and 6‐iso­butyl groups. The two compounds show similar molecular packing driven by strong O—H⋯O=C hydrogen bonds, leading to infinite chains in the crystal structure.     

Four cyclo­alkane­spiro‐4′‐imidazolidine‐2′,5′‐dithiones

The crystal structures of four cyclo­alkane­spiro‐4′‐imidazolidine‐2′,5′‐dithiones, namely cyclo­pentane­spiro‐4′‐imidazolidine‐2′,5′‐dithione {systematic name: 1,3‐diaza­spiro­[4.4]­nonane‐2,4‐dithione}, C₇H₁₀N₂S₂, cyclo­hexane­spiro‐4′‐imidazolidine‐2′,5′‐dithione {systematic name: 1,3‐diaza­spiro­[4.5]decane‐2,4‐dithione}, C₈H₁₂N₂S₂, cyclo­heptane­spiro‐4′‐imidazolidine‐2′,5′‐dithione {systematic name: 1,3‐diaza­spiro­[4.6]undecane‐2,4‐dithione}, C₉H₁₄N₂S₂, and cyclo­octane­spiro‐4′‐imidazolidine‐2′,5′‐dithione {systematic name: 1,3‐di­aza­spiro­[4.7]dodecane‐2,4‐dithione}, C₁₀H₁₆N₂S₂, have been determined. The three‐dimensional packing in all of the structures is based on closely similar chains, in which hydantoin moieties are linked through N—H⋯S hydrogen bonding. The size of the cyclo­alkane moiety influences the degree of its deformation. In the cyclo­octane compound, the cyclo­octane ring assumes both boat–chair and boat–boat conformations.     

Two 2,2‐dihalo‐N‐(1‐phenyl­ethyl)­cyclo­propane‐1‐carbox­amides

The crystal structures of (1R,1′S)‐2′,2′‐di­chloro‐N‐(1‐phenyl­ethyl)­cyclo­propane‐1′‐carbox­amide, C₁₂H₁₃Cl₂NO, (I), and (1R,1′R)‐2′,2′‐di­fluoro‐N‐(1‐phenyl­ethyl)­cyclo­propane‐1′‐car­box­amide, C₁₂H₁₃F₂NO, (II), have been determined. Both crystals contain two independent mol­ecules with different conformations of the phenyl­ethyl groups. In the crystals of both compounds, the mol­ecules are linked together by N—H⃛O hydrogen bonds, thus forming chains in the a direction.     

Di­bromo­[(–)‐sparteine‐κ2N,N′]­zinc(II)

In the title compound, di­bromo­[(6R,7S,8S,14S)‐1,3,4,7,7a,8,9,10,11,13,14,14a‐dodeca­hydro‐7,14‐methano‐2H,6H‐dipyrido­[1,2‐a:1′,2′‐e][1,5]­diazo­cine‐κ²N,N′]­zinc(II), [ZnBr₂(C₁₅H₂₆N₂)], the chiral nitro­gen‐chelating alkaloid (?)‐l ‐sparteine acts as a bidentate ligand, with two bromide ligands occupying the remaining coordination sites, producing a slightly distorted tetrahedral structure. The dihedral angle between the N—Zn—N and Br—Zn—Br planes is 82.4 (1)°. The distortion of the tetrahedral coordination is demonstrated by the fact that the midpoint of the N?N line does not lie in the Br—Zn—Br plane, but is tilted towards one of the N atoms by 0.164 Å. Similarly, the midpoint of the Br?Br line is tilted towards one of the Br atoms by 0.117 Å.     

Stereochemistry of two new polyfunctionalized gem‐dihalo­cyclo­propanes

The two new gem‐dihalogeno­cyclo­propanes (1′S,3R)‐3‐(2′,2′‐di­chloro‐1′‐methyl­cyclo­propyl)‐6‐oxoheptanoic acid, C₁₁H₁₆­Cl₂O₃, (2), and (1′S,3R)‐3‐(2′,2′‐di­bromo‐1′‐methyl­cyclo­propyl)‐6‐oxoheptanoic acid, C₁₁H₁₆Br₂O₃, (3), are isostructural. Both present two stereogenic centers at C1′ and C3. The absolute configuration was determined by X‐ray methods. The cyclo­propyl rings are unsymmetrical, the shortest bond being distal with respect to the alkyl‐substituted C atom.     

Carbocyclic 5′‐norcytidine (5′‐norcarbodine)

A preparation of (1′R,2′S,3′R,4′S)‐1‐(2′,3′,4′‐trihydroxycyclopent‐1′‐yl)‐lH‐cytosine (5′‐norcarbodine, 3 ) has formally been achieved in 2 steps from (+)‐(1R,4S)‐4‐hydroxy‐2‐cyclopenten‐1‐yl acetate ( 4 ) and cytosine. The L‐like enantiomer of 3 (that is, 6 ) is also reported using the enantiomer of 4 (that is, 7 ). In evalu ating 3 and 6 for antiviral potential against a number of viruses, compound 3 was found to have activity towards Epstein‐Barr virus (EBV).     

Non‐iterative Asymmetric Synthesis of C15 Polyketide Spiroketals

The 2,2′‐methylenebis[furan] ( 1 ) was converted to 1‐{(4R,6S))‐6‐[(2R)‐2,4‐dihydroxybutyl]‐2,2‐dimethyl‐1,3‐dioxan‐4‐yl}‐3‐[(2R,4R)‐tetrahydro‐4,6‐dihydroxy‐2H‐pyran‐2‐yl)propan‐2‐one ((+)‐ 18 ) and its (4S)‐epimer (?)‐ 19 with high stereo‐ and enantioselectivity (Schemes 1–3). Under acidic methanolysis, (+)‐ 18 yielded a single spiroketal, (3R)‐4‐{(1R,3S,4′R,5R,6′S,7R)‐3′,4′,5′,6′‐tetrahydro‐4′‐hydroxy‐7‐methoxyspiro[2,6‐dioxabicyclo[3.3.1]nonane‐3,2′‐[2H]pyran]‐6′‐yl}butane‐1,3‐diol ((?)‐ 20 ), in which both O‐atoms at the spiro center reside in equatorial positions, this being due to the tricyclic nature of (?)‐ 20 (methyl pyranoside formation). Compound (?)‐ 19 was converted similarly into the (4′S)‐epimeric tricyclic spiroketal (?)‐ 21 that also adopts a similar (3S)‐configuration and conformation. Spiroketals (?)‐ 20 , (?)‐ 21 and analog (?)‐ 23 , i.e., (1R,3S,4′R,5R,6′R)‐3′,4′,5′,6′‐tetrahydro‐6′‐[(2S)‐2‐hydroxybut‐3‐enyl]‐7‐methoxyspiro[2,6‐dioxabicyclo[3.3.1]nonane‐3,2′‐[2H]pyran]‐4′‐ol, derived from (?)‐ 20 , were assayed for their cytotoxicity toward murine P388 lymphocytic leukemia and six human cancer cell lines. Only racemic (±)‐ 21 showed evidence of cancer‐cell‐growth inhibition (P388, ED₅₀: 6.9 μg/ml).     

Solvent‐ and Temperature‐Controlled In Situ Ligand Reactions Mediated by CuII and 3′‐[(E)‐{[(1S,2S)‐2‐Aminocyclohexyl]imino}methyl]‐4′‐hydroxy‐4‐biphenylcarboxlic Acid

Three new compounds, CuL, CuL′, and Cu₂O₂L′′₂ (H₂L=3′‐[(E)‐{[(1S,2S)‐2‐aminocyclohexyl]imino}methyl]‐4′‐hydroxy‐4‐biphenylcarboxlic acid, H₂L′=3′‐[(E)‐{[(1S,2S)‐2‐aminocyclohexyl]imino}methyl]‐4′‐hydroxy‐5′‐nitro‐4‐biphenylcarboxlic acid, H₂L′′=3′‐(N,N‐dimethylamino methyl)‐4′‐hydroxy‐4‐biphenylcarboxlic acid), were selectively synthesized through a controlled in situ ligand reaction system mediated by copper(II) nitrate and H₂L. Selective nitration was achieved by using different solvent mixtures under relatively mild conditions, and an interesting and economical reductive amination system in DMF/EtOH/H₂O was also found. All crystal structures were determined by single‐crystal X‐ray diffraction analysis. Both CuL and CuL′ display chiral 1D chain structures, whereas Cu₂O₂L′′₂ possesses a structure with 13×16 Å channels and a free volume of 41.4 %. The possible mechanisms involved in this in situ ligand‐controlled reaction system are discussed in detail.     

Bis(2,4,7‐tri­methyl­indenyl)­cobalt(II) and rac‐2,2′,4,4′,7,7′‐hexamethyl‐1,1′‐biindene

The crystal and molecular structures of bis(η⁵‐2,4,7‐tri­methyl­indenyl)­cobalt(II), [Co(C₁₂H₁₃)₂], (I), and rac‐2,2′,4,4′,7,7′‐hexamethyl‐1,1′‐biindene, C₂₄H₂₆, (II), are reported. In the crystal structure of (I), the Co atom lies on an inversion centre and the structure represents the first example of a bis(indenyl)cobalt complex exhibiting an eclipsed indenyl conformation. The (1R,1′R) and (1S,1′S) enantiomers of the three possible stereoisomers of (II), which form as by‐products in the synthesis of (I), cocrystallize in the monoclinic space group P2₁/c. In the unit cell of (II), alternating (1R,1′R) and (1S,1′S) enantiomers pack in non‐bonded rows along the a axis, with the planes of the indenyl groups parallel to each other and separated by 3.62 and 3.69 Å.     

Two stereoisomeric pentacyclic oxin­dole alkaloids from Uncaria tomentosa: uncarine C and uncarine E

The chloro­form solvate of uncarine C (pteropodine), (1′S,3R,4′aS,5′aS,10′aS)‐1,2,5′,5′a,7′,8′,10′,10′a‐octa­hydro‐1′‐methyl‐2‐oxospiro­[3H‐indole‐3,6′(4′aH)‐[1H]­pyrano­[3,4‐f]indolizine]‐4′‐carboxyl­ic acid methyl ester, C₂₁H₂₄N₂O₄·CHCl₃, has an absolute configuration with the spiro C atom in the R configuration. Its epimer at the spiro C atom, uncarine E (isopteropodine), (1′S,3S,4′aS,5′aS,10′aS)‐1,2,5′,5′a,7′,8′,10′,10′a‐octahydro‐1′‐methyl‐2‐oxospiro[3H‐indole‐3,6′(4′aH)‐[1H]pyrano[3,4‐f]indolizine]‐4′‐carboxylic acid methyl ester, C₂₁H₂₄N₂O₄, has Z′ = 3, with no solvent. Both form intermolecular hydrogen bonds involving only the ox­indole, with N?O distances in the range 2.759 (4)–2.894 (5) Å.     

A pair of epimeric 13‐hydroxy‐2,3,6,7‐tetra­methoxy‐8b,11,12,12a,13,13a‐hexa­hydro‐9H‐9a‐aza­cyclo­penta­[b]tri­phenyl­ene‐10‐ones

The structures of two compounds which are intermediates in the synthesis of phenanthroindolizidine alkaloids have been determined. (8bS,13aS,14R,14aR)‐8b,9,11,12,13,13a,14,14a‐Octa­hydro‐14‐hydroxy‐2,3,6,7‐tetra­methoxy­dibenzo­[f,h]pyrrolo[1,2‐b]­isoquinolin‐11‐one acetone solvate, C₂₄H₂₇NO₆·C₃H₆O, (II), crystallizes in a chiral space group with one solvent mol­ecule (acetone) present in the asymmetric unit. On the other hand, (8bS,13aS,14S,14aR)‐8b,9,11,12,13,13a,14,14a‐octa­hydro‐14‐hydroxy‐2,3,6,7‐tetra­methoxy­dibenzo­[f,h]pyrrolo[1,2‐b]­isoquinolin‐11‐one, C₂₄H₂₇NO₆, (III), crystallizes in a centrosymmetric space group with two mol­ecules in the asymmetric unit and with no solvent present. The two mol­ecules in the asymmetric unit of (III) are structurally the same. Compounds (II) and (III) are epimers at the C atom carrying the OH group; otherwise they are very similar in structure.     

A 1,3,2‐ox­aza­borolidine dimer derived from (S)‐α,α‐di­phenyl­prolinol

The reaction of (S)‐α,α‐di­phenyl­prolinol with an excess of borane–tetra­hydro­furan complex yields a stable crystalline material with the composition C₃₄H₃₈B₂N₂O₂, which features a borane adduct of a spiro­cyclic structure with two ox­aza­borolidine rings joined by a central tetrahedral B atom. This dimeric ox­aza­borolidine complex, viz. 3,3,3′,3′‐tetra­phenyl‐1,1′‐spiro­bi(3a,4,5,6‐tetra­hydro‐3H‐pyrrolo­[1,2‐c][1,3,2]­ox­azaborole)–7‐borane, is the dominant product under various reaction conditions; its crystal structure is consistent with ¹¹B, ¹H and ¹³C NMR and IR analyses.     

Solid‐state conformations of linear depsipeptide amides with an alternating sequence of α,α‐disubstituted α‐amino acid and α‐hydroxy acid

Depsipeptides and cyclodepsipeptides are analogues of the corresponding peptides in which one or more amide groups are replaced by ester functions. Reports of crystal structures of linear depsipeptides are rare. The crystal structures and conformational analyses of four depsipeptides with an alternating sequence of an α,α‐disubstituted α‐amino acid and an α‐hydroxy acid are reported. The molecules in the linear hexadepsipeptide amide in (S)‐Pms‐Acp‐(S)‐Pms‐Acp‐(S)‐Pms‐Acp‐NMe₂ acetonitrile solvate, C₄₇H₅₈N₄O₉·C₂H₃N, ( 3b ), as well as in the related linear tetradepsipeptide amide (S)‐Pms‐Aib‐(S)‐Pms‐Aib‐NMe₂, C₂₈H₃₇N₃O₆, ( 5a ), the diastereoisomeric mixture (S,R)‐Pms‐Acp‐(R,S)‐Pms‐Acp‐NMe₂/(R,S)‐Pms‐Acp‐(R,S)‐Pms‐Acp‐NMe₂ (1:1), C₃₂H₄₁N₃O₆, ( 5b ), and (R,S)‐Mns‐Acp‐(S,R)‐Mns‐Acp‐NMe₂, C₃₀H₃₇N₃O₆, ( 5c ) (Pms is phenyllactic acid, Acp is 1‐aminocyclopentanecarboxylic acid and Mns is mandelic acid), generally adopt a β‐turn conformation in the solid state, which is stabilized by intramolecular N—H…O hydrogen bonds. Whereas β‐turns of type I (or I′) are formed in the cases of ( 3b ), ( 5a ) and ( 5b ), which contain phenyllactic acid, the torsion angles for ( 5c ), which incorporates mandelic acid, indicate a β‐turn in between type I and type III. Intermolecular N—H…O and O—H…O hydrogen bonds link the molecules of ( 3a ) and ( 5b ) into extended chains, and those of ( 5a ) and ( 5c ) into two‐dimensional networks.     

The diastereoisomers methyl 5‐(S)‐[2‐(R)/(S)‐methoxycarbonyl)‐2,3,4,5‐tetrahydropyrrol‐1‐ylcarbonyl]‐1‐(4‐methylphenyl)‐4,5‐dihydropyrazole‐3‐carboxylate

The title diastereoisomers, methyl 5‐(S)‐[2‐(S)‐methoxy­carbonyl)‐2,3,4,5‐tetra­hydro­pyrrol‐1‐yl­carbonyl]‐1‐(4‐methyl­phenyl)‐4,5‐di­hydro­pyrazole‐3‐carboxyl­ate and methyl 5‐(S)‐[2‐(R)‐methoxycarbonyl)‐2,3,4,5‐tetrahydropyrrol‐1‐ylcarbonyl]‐1‐(4‐methyl­phenyl)‐4,5‐di­hydro­pyrazole‐3‐carboxylate, both C₁₉H₂₃N₃O₅, have been studied in two crystalline forms. The first form, methyl 5‐(S)‐[2‐(S)‐methoxy­carbonyl)‐2,3,4,5‐tetrahydropyrrol‐1‐ylcarbonyl]‐1‐(4‐methylphenyl)‐4,5‐di­hydro­pyrazole‐3‐carboxyl­ate–methyl 5‐(S)‐[2‐(R)‐methoxy­carbonyl)‐2,3,4,5‐tetra­hydro­pyrrol‐1‐yl­carbonyl]‐1‐(4‐methylphenyl)‐4,5‐dihydropyrazole‐3‐carboxylate (1/1), 2(S),5(S)‐C₁₉H₂₃N₃O₅·2(R),5(S)‐C₁₉H₂₃N₃O₅, contains both S,S and S,R isomers, while the second, methyl 5‐(S)‐[2‐(S)‐methoxycarbonyl)‐2,3,4,5‐tetrahydro­pyrrol‐1‐ylcarbonyl]‐1‐(4‐methyl­phenyl)‐4,5‐di­hydro­pyrazole‐3‐carboxyl­ate, 2(S),5(S)‐C₁₉H₂₃N₃O₅, is the pure S,S isomer. The S,S isomers in the two structures show very similar geometries, the maximum difference being about 15° on one torsion angle. The differences between the S,S and S,R isomers, apart from those due to the inversion of one chiral centre, are more remarkable, and are partially due to a possible rotational disorder of the 2‐­(methoxycarbonyl)tetrahydropyrrole group.     

(±)‐6‐tert‐Butyl‐8‐hydroxymethyl‐2‐­phenyl‐4H‐1,3‐benzodioxin and 2,2,2′,2′,6,6′‐hexamethyl‐8,8′‐methylenebis(4H‐1,3‐benzodioxin)

Two compounds containing 1,3‐benzodioxin groups are reported, namely (±)‐6‐tert‐butyl‐8‐hydroxy­methyl‐2‐phenyl‐4H‐1,3‐benzodioxin, C₁₉H₂₂O₃, (I), and 2,2,2′,2′,6,6′‐hexamethyl‐8,8′‐methyl­enebis(4H‐1,3‐benzodioxin), C₂₃H₂₈O₄, (II).The hydroxy groups of neighbouring mol­ecules in (I) are hydrogen bonded to each other, giving rise to double‐row chains. The mol­ecule in (II) adopts a `butterfly' conformation, with the O atoms in distal positions. In both compounds, the dioxin rings are in distorted half‐chair conformations.     

The α‐d anomer of 5‐aza‐7‐deaza‐2′‐deoxyguanosine

In the monohydrate of 2‐amino‐8‐(2‐deoxy‐α‐d ‐erythro‐pento­furan­osyl)‐8H‐imidazo­[1,2‐a]­[1,3,5]­triazin‐4‐one, C₁₀H₁₃N₅O₄·H₂O, denoted (I) or αZ_d, the conformation of the N‐gly­cosyl­ic bond is in the high‐anti range [χ = 87.5 (3)°]. The 2′‐deoxy­ribo­furan­ose moiety adopts a C2′‐endo,C3′‐exo(^2′T_3′) sugar puckering (S‐type sugar) and the conformation at the C4′—C5′ bond is ?sc (trans).