bluuebunny/crossref_metadata_2025_split huggingface dataset:
New Results in the Synthesis of Styrylazulene Derivatives: Application of the ‘Anil synthesis’ to the preparation of azulenes substituted with styryl groups at the seven‐membered ring
Authors: Briquet Anne Andrée Sophie , Hansen Hans‐Jürgen 
Published: December 2004

AbstractThe synthesis of 4,6,8‐trimethyl‐1‐[(E)‐4‐R‐styryl]azulenes 5 (R=H, MeO, Cl) has been performed by Wittig reaction of 4,6,8‐trimethylazulene‐1‐carbaldehyde (1) and the corresponding 4‐(R‐benzyl)(triphenyl)phosphonium chlorides 4 in the presence of EtONa/EtOH in boiling toluene (see Table 1). In the same way, guaiazulene‐3‐carbaldehyde (2) as well as dihydrolactaroviolin (3) yielded with 4a the corresponding styrylazulenes 6 and 7, respectively (see Table 1). It has been found that 1 and 4b yield, in competition to the Wittig reaction, alkylation products, namely 8 and 9, respectively (cf. Scheme 1). The reaction of 4,6,8‐trimethylazulene (10) with 4b in toluene showed that azulenes can, indeed, be easily alkylated with the phosphonium salt 4b. 4,6,8‐Trimethylazulene‐2‐carbaldehyde (12) has been synthesized from the corresponding carboxylate 15 by a reduction (LiAlH4) and dehydrogenation (MnO2) sequence (see Scheme 2). The Swern oxidation of the intermediate 2‐(hydroxymethyl)azulene 16 yielded only 1,3‐dichloroazulene derivatives (cf. Scheme 2). The Wittig reaction of 12 with 4a and 4b in the presence of EtONa/EtOH in toluene yielded the expected 2‐styryl derivatives 19a and 19b, respectively (see Scheme 3). Again, the yield of 19b was reduced by a competing alkylation reaction of 19b with 4b which led to the formation of the 1‐benzylated product 20 (see Scheme 3). The ‘anil synthesis’ of guaiazulene (21) and the 4‐R‐benzanils 22 (R=H, MeO, Cl, Me2N) proceeded smoothyl under standard conditions (powered KOH in DMF) to yield the corresponding 4‐[(E)‐styryl]azulene derivatives 23 (see Table 4). In minor amounts, bis(azulen‐4‐yl) compounds of type 24 and 25 were also formed (see Table 4). The ‘anil reaction’ of 21 and 4‐NO2C6H4CH=NC6H5 (22e) in DMF yielded no corresponding styrylazulene derivative 23e. Instead, (E)‐1,2‐bis(7‐isopropyl‐1‐methylazulen‐4‐yl)ethene (27) was formed (see Scheme 4). The reaction of 4,6,8‐trimethylazulene (10) and benzanil (22a) in the presence of KOH in DMF yielded the benzanil adducts 28 to 31 (cf. Scheme 5). Their direct base‐catalyzed transformation into the corresponding styryl‐substituted azulenes could not be realized (cf. Scheme 6). However, the transformation succeeded smoothly with KOH in boiling EtOH after N‐methylation (cf. Scheme 6).
Glycosylidene Carbenes. Part 19. Regioselective glycosidation of allyl 2‐deoxy‐2‐phthalimido‐D‐allopyranosides
Authors: Briner Karin , Bernet Bruno , Maloisel Jean‐Luc , Vasella Andrea 
Published: December 2004

AbstractThe regio‐ and stereoselectivity of the glycosidation of the partially protected mono‐alcohols 3 and 7, the diols 2 and 8, and the triol 4 by the diazirine 1 have been investigated. Glycosidation of the α‐D‐diol 2 (Scheme 2) gave regioselectively the 1,3‐linked disaccharides 11 and 12 (80%, α‐D/β‐D 9:1), whereas the analogous reaction with the βD‐anomer 8 led to a mixture of the anomeric 1,3‐ and 1,4‐linked disaccharides 13 (12.5%), 14 (16%), 15 (13%), and 16 (20.5%; Table 2). Protonation of the carbene by OH–C(4) of 2 is evidenced by the observation that the α‐D‐mono‐alcohol 3 did not react with 1 under otherwise identical conditions, and that the β‐D‐alcohol 7 yielded predominantly the β‐D‐glucoside 18 (52%) besides 14% of 17. Similarly as for the glycosidation of the diol 2, the influence of the H‐bond of HOC(4) on the direction of approach of the carbene, the role of HOC(4) in protonating the carbene, and the stereoelectronic control in the interception of the ensuring oxycarbenium cation are evidenced by the reaction of the triol 4 with 1 (Scheme 3), leading mostly to the α‐D‐configurated 1,3‐linked disaccharide 19 (41%), besides its anomer 20 (16%), and some 4‐substituted β‐D‐glucoside 21 (9%). No 1,6‐linked disaccharides could be detected. In agreement with the observed reactivity, the 1H‐NMR and IR spectra reveal a strong H‐bond between HOC(3) and the phthalimido group in the α‐D‐, but not in the β‐D‐allosides. The different H‐bonds in the anomeric phthalimides are in keeping with the results of molecular‐mechanics calculations.
Preparation and Transmetallation of a Triphenylstannyl β‐D‐Glucopyranoside: A highly stereoselective route to β‐D‐C‐glycosides via glycosyl dianions
Authors: Frey Oliver , Hoffmann Matthias , Wittmann Valentin , Kessler Horst , Uhlmann Peter , Vasella Andrea 
Published: December 2004

AbstractThe triphenylstannyl β‐D‐glucopyranoside 4 was synthesized in one step from the 1,2‐anhydro‐α‐D‐glucopyranose 3 with (triphenylstannyl)lithium (Scheme 1). Transmetallation of 4 with excess BuLi, followed by quenching the dianion 7 with CD3OD gave (1S)‐1,5‐anhydro‐3,4,6‐tri‐O‐benzyl‐[1‐2H]‐D‐ glucitol (8) in 81% yield (Scheme 2). Trapping of 7 with benzaldehyde, isobutyraldehyde, or acroleine gave the expected β‐D‐configurated products 11, 12, and 13 in good yields. Preparation of C‐acyl glycosides from acid chlorides, such as acetyl or benzoyl chloride was not practicable, but addition of benzonitrile to 7 yielded 84% of the benzoylated product 14. Treatment of 7 with MeI led to 15 (30%) along with 40% of 18, C‐alkylation being accompanied by halogen‐metal exchange. Prior addition of lithium 2‐thienylcyanocuprate increased the yield of 15 to 50% and using dimethyl sulfate instead of MeI led to 77% of 15. No α‐D‐anomers could be detected, except with allyl bromide as the electrophile, which yielded in a 1:1 mixture of the anomers 16 and 17.
Quantum Chemical Investigation of the Structure and Reactivity of Indole Derivatives of Tricarbonylchromium(0)
Authors: Furet Eric , Savary François , Weber Jacques , Kündig Ernst Peter 
Published: December 2004

AbstractIn a theoretical investigation of the structure and reactivity of indole derivatives of tricarbonylchromium(0), we have used two different semi‐empirical quantum chemical models derived from the extended Hückel molecular‐orbital (EHMO) formalism. The first one, based on the atom‐superposition and electron‐delocalization (ASED) method, is used to optimize the geometry of the systems; it is shown to lead to results in satisfactory agreement with experiment in the case of the complex for which X‐ray structural data are available, the average errors being 0.03–0.05 Å for bond distances and 5° for bond angles. The second one consists of a local reactivity index, made of the intermolecular interaction energy between the organometallic substrate and a model reactant. It is seen that this procedure is able to reproduce the experimental trends as to the most reactive regions of the systems investigated towards nucleophilic and electrophilic addition reactions.
Synthesis of Aristotelia‐Type Alkaloids. Part XIII. Total syntheses of (+)‐makonine, (+)‐aristotelinone, and (+)‐11,12‐didehydroaristoteline
Authors: Stahl Reto , Galli Renato , Güller Rolf , Borschberg Hans‐Jürg 
Published: December 2004

AbstractThe oxidative transformation of synthetic (+)‐aristoteline ((+)‐6) into other metabolites which had been isolated from Aristotelia species was investigated. Thus, treatment of (+)‐6 with I2 as the single oxidant furnished the naturally occurring indole alkaloids (+)‐makonine ((+)‐9),(+)‐aristotelinone ((+)‐11), or (+)‐11, 12‐didehydroaristoteline ((+)‐7) in good yields, the selectivity of the oxidation process depending on the chosen reaction conditions.
A Practical Synthesis of (2S, 3R)‐3‐Amino‐2‐methylpentanoic Acid from L‐Aspartic Acid
Authors: Jefford Charles W. , McNulty James 
Published: December 2004

AbstractL‐Aspartic acid by successive N‐tosylation, anhydride formation, and reduction was converted into (3S)‐3‐(tosylamino)butano‐4‐lactone (4). Electrophilic methylation of 4, subsequent iodo‐esterification and nucleophilic methylation, followed by saponification and deprotection, gave (2S, 3R)‐3‐amino‐2‐methylpentanoic acid (2) with an ee of > 99% in seven steps and in an overall yield of 34%.
Insertion Reactions of [ReH(CO)5–n(PMe3)n] Complexes (n = 2–4) with aldehydes, CO2, and activated acetylenes
Authors: Nietlispach Daniel , Veghini Dario , Berke Heinz 
Published: December 2004

AbstractThe complexes of the type [ReH(CO)5–n(PMe3)n] (n = 4, 3) were reacted with aldehydes, CO2, and RCCCOOMe (R = H, Me) to establish a phosphine‐substitutional effect on the reactivity of the Re–H bond. In the series 1–3, benzaldehyde showed conversion with only 3 to afford a (benzyloxy)carbonyltetrakis(trimethylphosphine)rhenium complex 4. Pyridine‐2‐carbaldehyde allowed reaction with all hydrides 1–3. With 1 and 2, the same dicarbonyl[(pyridin‐2‐yl)methoxy‐O, N]bis(trimethylphosphine)rhenium 5b was formed with the intermediacy of a [(pyridin‐2‐yl)methoxy‐O]‐ligated species and extrusion of CO or PMe3, respectively. The analogous conversion of 3 afforded the carbonyl[(pyridin‐2‐yl)methoxy‐O,N]tris(trimethylphosphine)rhenium (1) 7b. While 1 did not react with CO2, 2 and 3 yielded under relatively mild conditions the formato‐ligated [Re(HCO2)(CO)(L)(PMe3)3] species (8 (L = CO) and 9 (L = PMe3)). Methyl propiolate and methyl butynoate were transformed, in the presence of 1, to [Re{C(CO2Me)CHR}(CO)3(PMe3)2] systems (10a (R = H), and 10b(R = Me)), with prevailing α‐metallation and trans‐insertion stereochemistry. Similarly, HC≡CCO2Me afforded with 2 and 3, the α‐metallation products [Re{C(CO2Me)CH2}(CO)(L)(PMe3)3] 11 (L = CO) and 12(L = PMe3). The methyl butyonate insertion into 2 resulted in formation of a mixture of the (Z)‐ and (E)‐isomers of [Re{C(CO2Me)CHMe} (CO)2(PMe3)3] (13a,b). In the case of the conversion of 3 with MeCCCO2Me, a Re–H cis‐addition product [Re{(E)‐C(CO2Me)CHMe}(CO)(PMe3)4] (14) was selectively obtained. Complex 11 was characterized by an X‐ray crystal‐structure analysis.
Chemische Reaktionen mit Fischer‐Carben‐Komplexen des 1,6‐Methano[10]annulens
Authors: Neidlein Richard , Gürtler Stephan , Krieger Claus 
Published: December 2004

Reactions of Fischer Carbene Complexes of 1,6‐Methano[10]annuleneThe new Fischer carbene complexes 7, 8, and 10 of 1,6‐methano[10]annulene as well as the bis(carbene) complex 15, were readily available in moderate yields by using the classical Fischer method (Schemes 1 and 2). The complexes 5 and 7 reacted easily with several alkynes under benzo‐annulation conditions (Dötz reaction). Depending on the workup conditions, the new benzoquinones 16 and 17 (Scheme 5), hydroquinones 19 and 20 (Scheme 6), and protected hydroquinones 23–25 (Schemes 6 and 7) were synthesized. Surprisingly, in one run we were able to isolate the air‐stable [Cr(η6‐arene)(CO)3] complex 26 (Scheme 7). The X‐ray structure and NMR data of 26 established a remarkable perturbation of the 10π perimeter of the 1,6‐methano[10]annulene part in the hydroquinones 19–26, but no evidence of a σ‐homoaromatic “bis(trinorcaradiene)” system. The first double Dötz reaction of 15 with hex‐3‐yne resulted in the formation of the “anti”‐dibenzo‐annulated 1,6‐methano[10]annulene 32 (Scheme 8), which does not exist furthermore as a π‐homoaromatic system, but as its σ‐homoaromatic valence isomer.
Diazoaldehyde Chemistry. Part 1. Transdiazotization of Acylacetaldehydes in Neutral‐to‐Acidic Medium. A Direct Approach to the Synthesis of α‐Diazo‐β‐oxoaldehydes
Authors: Sezer Özkan , Anaç Olcay 
Published: December 2004

AbstractFirst ever non‐deformylating transdiazotization of acylacetaldehydes was achieved: the reactions of 2‐azido‐l‐ethylpyridinium tetrafluoroborate (4) with acylacetaldehydes3proceeded partially without deformylation to yield 16 new α‐diazo‐β‐oxoaldehydes1along with diazomethyl ketones2, especially in the presence of NaOAc (Scheme 1, Tables 1and2). The product distribution was substituent‐dependent and could be correlated quantitatively. This new diazotization reaction appears as an alternative, direct, and more general method for the synthesis of these diazooxoaldehydes. α‐Oxocycloalkanecarbaldehydes5gave only traces (if any) of α‐diazocycloalkanones7, and rearrangement products6were isolated (Scheme 2). Mechanisms of the reactions are discussed (Schemes 4and5).
Glycosylidene Carbenes. Part 20. Synthesis of deprotected, spiro‐linked C‐glycosides of C60
Authors: Uhlmann Peter , Harth Eva , Naughton Andrew B. , Vasella Andrea 
Published: December 2004

AbstractMannosylidenation of buckminsterfullerene (C60; 1) with the 2,3‐di‐O‐benzyl‐4,6‐O‐benzylidene‐protected diazirine 7 and the 2,3:4,6‐di‐O‐isopropylidene‐protected diazirine 8 leads to the spiro‐linked C ‐glycosides 6 and 10 in 44 and 31% yield, respectively (Scheme). The diazirine 8 was prepared in five steps from 2,3:4,6‐di‐O‐iso‐propylidene‐α‐D‐mannopyranose (11) via the oximes 12, the (Z)‐hydroximolactone 13, the mesylate 14, and the diaziridines 15. Deprotection of the mannosylidenated fullerenes 6 and 10 under acidic conditions gave the partially deprotected diol 9 (97%) and the unprotected mannosylidenated fullerene 16 (73%), respectively. The mannosylidene‐fullerenes 6, 9, 10, and 16 possess a 6–6 ring‐bridged σ‐homoaromatic structure.
Conformational Features of 7,8,13β,14α‐Tetrahydro‐N7‐methylcorysaminium, a biosynthetic intermediate to the protopine‐type alkaloid corycavine
Authors: Kamigauchi Miyoko , Noda Yuko , Iwasa Kinuko , Nishijo Zjujiro , Ishida Thoshimasa , In Yasuko 
Published: December 2004

AbstractThe crystal structure of (±)‐7,8,13β,14α‐tetrahydro‐N7‐(13C)methylcorysaminium iodide (13C‐3a·I) was investigated by X‐ray analysis and thus the relative configuration (7S*,13S*,14S*) established (Fig. 1). The conformation of 3a was shown to have a cis‐junction of the B/C rings and the rings A and D in an antiperiplanar position relative to the C(13)C(14) bond (‘anti‐cis’), a twisted half‐chair for ring B, and a half‐chair for ring C (Figs. 2 and 3). Conformation analysis by 1H‐NMR data indicated that the crystal conformation of 3a is also the preferred one in MeOH solution.
Les β‐cétonitriles groupes protecteurs de la fonction amine. Préparation d'amino‐alcools
Authors: Abarbri Mohamed , Guignard Alain , Lamant Maurice 
Published: December 2004

β‐Ketonitrile‐Derived Protecting Groups of the Amino Function. Synthesis of Amino AlcoholsThe amino group of natural L‐amino acid esters is protected by condensation with 2‐oxocyclopentanenitrile (1) or 2‐formyl‐2‐phenylacetonitrile (10). Only the ester group of the formed cyanoenamino esters 2 and 11 reacts with nucleophilic reagents such as organometallics (RMgX, RLi), borohydrides, or metal amides, whereas the cyanoenamino group is unchanged (Schemes 1 and 2). Cyanoenamino alcohols obtained by reduction of cyanoenamino esters 2 are hydrolyzed under acidic conditions to amino alcohols with retention of the configuration of the starting amino acid. This sequence of reactions allows to prepare derivatives of L‐tyrosinol from (−)‐L‐tyrosine (see, e.g., Scheme 4). Cyanoenamino esters 11 are readily methylated at the N‐atom to give N‐methylated cyanoenamino esters (Scheme 3). This property is exploited on the way of a multistep procedure to obtain N‐methylated amino alcohols homologous to natural (−)‐(1R,2S)‐ephedrine.
Selectivity in Rhodium(II)‐Catalyzed Rearrangements of cycloprop‐2‐ene‐1‐carboxylates
Authors: Müller Paul , Gränicher Christian 
Published: December 2004

AbstractThe course of the thermocatalytic rearrangement of cycloprop‐2‐ene‐1‐carboxylates in the presence of dirhodium(II) tetrakis(perfluorobutyrate) ([Rh2(pfb)4]) was investigated by varying the substituents of the cyclopropene ring. Product composition is markedly influenced by the number, nature, and position of the substituents, which determine the regio‐ and stereoselectivity of the cyclopropene‐ring cleavage. A mechanism is proposed in which attack of the electrophilic RhII species is concerted with disrotatory ring opening of the incipient cyclopropyl cation and affords a metal‐complexed vinylcarbene. The chemoselectivity of the latter is consistent with that of other carbenes generated in the presence of [Rh2(pfb)4].
Synthesis of Benz[a]azulenes Substituted at the Benzo Ring
Authors: Fallahpour Reza‐Ali , Hansen Hans‐Jürgen 
Published: December 2004

AbstractIt is shown that the thermal electrocyclic ring‐closure reaction of 1,2‐di[(E)‐prop‐1‐enyl]benzene to yield 2,3‐dimethylnaphthalene (cf. Scheme 1) [10] can successfully be applied also to the synthesis of benz[a]azulenes (cf. Schemes 2 and 3). Starting materials are methyl 4,6,8‐trimethylazulen‐2‐yl ketone (6) and the corresponding 2‐carbaldehyde 5, which, in a Horner‐Emmons reaction, are transformed into the (azulen‐2‐yl)‐acrylates (E)‐8 and (E)‐7, respectively. Vilsmeier formylation of these compounds, followed by the Horner‐Emmons reaction leads to the formation of the bisacrylates (E,E)‐11 and (E,E)‐12, respectively. In an alternative reaction, (E)‐8, on treatment with dimethyl acetylenedicarboxylate (ADM) in the presence of [RuH2(PPh3)4], can be transformed into the methoxycarbonyl‐substituted bisacrylates (E,E)‐ and (E,Z)‐17. All three bisacrylates, on heating at 180–190° in p‐cymene, undergo cyclization to yield the corresponding dihydrobenz[a]azulenes 13, 14, and 18, respectively, which could easily be dehydrogenated on heating in the presence of Pd/C. The new benz[a]azulenes 15, 16, and 19 are fully characterized.
Unprecedented Ring Contractions in Cytochalasans: Formation of [10]cytochalasans and a cyclohepta[4,5]benz[1,2‐d]isoindole derivative
Authors: Boutellier Markus , Zürcher Werner , Tamm Christoph 
Published: December 2004

AbstractA series of transformations of cytochalasin D (1; zygosporin A) was carried out. After treatment of the diol 7 with mesyl chloride and pyridine, and subsequent chromatography on silica gel, the 17‐acetyl derivatives 12 and 13, the first members of the hitherto unknown [10]cytochalasans, were obtained. The alcohol 8 was converted to the chlorosulfinate 18 under the same conditions. Replacement of pyridine by triethylamine in the mesylation reaction led to the cyclohepta[4,5]benz[1,2‐d]isoindole derivative 20, also representing a novel ring system.
Synthesis of Aristotelia‐Type Alkaloids. Part XV. Total synthesis of (+)‐hobartinol
Authors: Dobler Markus , Anderson James C. , Juch Mathias , Borschberg Hans‐Jürg 
Published: December 2004

AbstractSynthetic (+)‐makomakine (6) was transformed in six steps into (+)‐17R,18R)‐17,18‐dihydrohobartine‐17,18‐diol ((+)‐5) with an overall yield of 38% (Scheme 2). This compound was shown to be identical with natural hobartinol, a monoterpene indole alkaloid from Aristotelia australasica, originally believed to be the (17S)‐epimer 1. At the same time, the synthesis of (+)‐5 delineates the hitherto unknown absolute configuration of this metabolite.
Stereoselective Synthesis of 2,4,6‐Trimethylcyclohex‐4‐ene‐1,3‐diol Derivatives and of polypropionate fragments with four contiguous stereogenic centers
Authors: Bialecki Maciej , Vogel Pierre 
Published: December 2004

AbstractThe Diels‐Alder adduct (±)‐3 of 2,4‐dimethylfuran and 1‐cyanovinyl acetate was converted stereoselectively into benzyl 6‐(4‐chlorophenylsulfonyl)‐1,3‐exo,5‐trimethyl‐7‐oxabicyclo[2.2.1]hept‐5‐en‐2‐exo‐yl (26) and ‐2‐endo‐yl ether (36). Addition of LiAlH4 to the latter led to the 3‐O‐benzyl derivatives 28 and 37 of (1RS,2SR,3SR,6SR)‐ and (1RS,2SR,3RS,6SR)‐5‐(4‐chlorophenylsulfonyl)‐2,4,6‐trimethylcyclohex‐4‐ene‐1,3‐diol, respectively. Methylenation of 6‐exo‐(4‐chlorophenylthio)‐1‐methyl‐5‐methylidene‐7‐oxabicyclo[2.2.1]heptan‐2‐one (16), obtained by reaction of (±)‐3 with 4‐Cl‐C6H4SCl and saponification gave, 6‐exo‐(4‐chlorophenylthio)‐1‐methyl‐3,5‐dimethylidene‐7‐oxabicyclo [2.2.1]heptan‐2‐one (43), the reduction of which with K‐Selectride afforded 6‐exo‐(4‐chlorophenylthio)‐1,3‐endo‐dimethyl‐5‐methylidene‐7‐oxabicyclo[2.2.1]heptan‐2‐endo‐ol (44). The 3‐O‐benzyl derivative 48 of (1RS,2RS,3RS,6SR)‐5‐(4‐chlorophenylsulfonyl)‐ 2,4,6‐trimethylcyclohex‐4‐ene‐1,3‐diol was derived from 44 via based‐induced oxa‐ring opening of benzyl 6‐endo‐(4‐chlorophenylsulfonyl)‐1,3‐endo‐5‐endo‐trimethyl‐7‐oxabicyclo[2.2.1]hept‐2‐endo‐yl ether (49). Benzylation of 28, followed by reductive desulfonylation and oxidative cleavage of the cyclohexene moiety afforded (2RS,3SR,4RS,5RS)‐3,5‐bis(benzyloxy)‐2,4‐dimethyl‐6‐oxoheptanal (32).
The X‐Ray Crystal Structures of a 1,9‐ and a 7,8‐Diels‐Alder monoadduct of C70
Authors: Seiler Paul , Herrmann Andreas , Diederich François 
Published: December 2004

AbstractAccurate low‐temperature X‐ray crystal structures of the isomeric Diels‐Alder monoadducts of C70 1a, bridged at the [6,6] bond between C(1) and C(9), and 1b, bridged at the [6,6] bond between C(7) and C(8), have been determined. The latter structure is the first one solved for a 7,8‐C70 monoadduct. The C1‐symmetrical 1a and Cs‐symmetrical 1b co‐crystallize with CS2 molecules in the space groups P21/c and Pnma, respectively, and the distances between bridgehead atoms are 1.603(3) and 1.584(3) Å. The degree of pyramidalization of atoms involved in [6,6] bonds near the ‘unsubstituted’ pole and near the equator of the fullerene was estimated; it is shown for the unsubstituted pole region that atoms corresponding to C(1) and C(9) are slightly more pyramidal than those corresponding to C(7) and C(8), in agreement with ab initio calculations obtained for the C70 spheroid. Some aspects of the crystal packings are discussed.
Crystal Structures of Two Modifications of [3,O‐didehydro‐mebmt1, val2]‐cyclosporin and comparison of three different X‐ray data sets
Authors: Pohl Ehmke , Herbst‐Irmer Regine , Sheldrick George M. , Dauter Zbigniew , Wilson Keith S. , Bölsterli Johann J. , Bollinger Pietro , Kallen Jörg , Walkinshaw Malcolm D. 
Published: December 2004

AbstractThe crystal structure of [3,O‐didehydro‐MeBmt1, Val2]cyclosporin (PSC‐833; 1) was investigated by X‐ray analysis. Data were collected from two different crystal modifications. Modification I crystallizes in P3121, a = b = 21.419 (2) Å, c = 32.101 (3) Å with one molecule in the asymmetric unit, modification II in P3221, a = b = 21.313 (2) Å, c = 62.053(3) Å with two molecules per asymmetric unit. This non‐immunosuppressive analogue of cyclosporin A adopts a similar backbone conformation to that found in the crystal structure of cyclosporin A and other analogues. Three different data sets of modification I were collected using an Enraf‐Nonius‐CAD4 diffractometer with CuKα radiation at 20°, a Stoe‐Siemens four‐circle diffractometer with MoKα radiation at − 120°, and an EMBL image‐plate scanner with synchrotron radiation at 12°. The quality of the data sets was evaluated by internal consistency, independent structure solution, and refinement. The structural parameters reported here for modification I are based on the synchrotron data.