bluuebunny/crossref_metadata_2025_split huggingface dataset:
Structural Aspects of the Enantioselectivity of Tartrates with α‐Amino‐alcohol Salts part. I. Crystal structures of eleven tartaric‐acid diesters
Authors: Egli Martin , Dobler Max 
Published: December 2004

AbstractEnantioselective host‐guest complexes of α‐amino‐alcohol salts with chiral tartaric‐acid esters can not be crystallised up to now. To study structural aspects of their enantioselectivity, crystal structures of the components were determined. The structures of eleven diesters with myrtanol, borneol, menthol, neomenthol, and cis‐4‐(tert‐butyl)cyclohexanol in different configurations showed a remarkable rigidity of the tartaric‐acid conformation, partly because of intramolecular H‐bonding between OH and C=O groups. The conformation of the tartaric‐acid part in these diesters is the same as the one observed in optically active tartaric acid (torsion angle OCCOH ca. 0°), The binding site for guest molecules is a parallelogram formed by two hydroxy and two carbonyl O‐atoms, all lying on the same side of a mean molecular plane. There is one exception: the dimenthyl ester, which is the most enantioselective with a norephedrine guest, has one of the ester groups turned (torsion angle OCCOH ca. 180°), forming a triangle of O‐atoms and moving the bulky menthyl group to the vicinity of the binding site.
Enantioselective Optode Membranes with Enantiomer Selectivity for (R)‐ and (S)‐l‐Phenylethylammonium Ions
Authors: Holý Petr , Morf Werner E. , Seller Kurt , Simon Wilhelm , Vigneron Jean‐Pierre 
Published: December 2004

AbstractThe recently developed general principle of ion‐selective optode membranes, based on conventional ionophores, was employed to design a new approach to the determination of enantiomeric excess. Highly lipophilic chiral crown derivatives, exhibiting a high selectivity for a chiral ammonium guest cation, are combined with a H+‐selective chromoionophore in a plasticized PVC membrane. The enantiomer recognition process is translated by this sensor with an optical transduction into a signal easily measured by a conventional spectrophotometer, and enantiomeric excess can be determined without the need for polarized light. Characteristics and a theoretical description of these new optode membranes are given.
2‐Aza‐l, 3‐dienes. Partie 6. Observation d′un effet ‘tert‐amino’ dans le traitement acide de (pyrrolidin‐l‐yl)‐azadienes
Authors: Legroux Didier , Brotn Jacques , Fleury Jean Pierre 
Published: December 2004

‘tert‐Amino Effect’ on Acidic Treatment of (Pyrrolidin‐l‐yl)azadienesThe behaviour of 4‐morpholino‐ and 4‐(pyrrolidin‐l‐yl)‐2‐aza‐1. 3‐diene‐l, l‐dicarbonitriles 3, and 4 and 10, respectively, in acidic medium is described. The former gives with HBr/AcOH 3‐bromopyrazine‐2‐carbonitrile 6. On the other hand, pyrrolidin‐1‐yl derivatives 4 and 10 furnish, by a [1, 5]‐H shift, pyrrolo[l, 2]pyrazine structures 5 and 11, respectively.
Synthesis of IH‐Cyclopropal[g]quinoline via Trapping of an ortho‐Quinodimethane
Authors: Müller Paul , Schaller Jean‐Pierre 
Published: December 2004

Abstract1H‐Cyclopropa[g]quinoline (3‐aza‐lH‐cyclopropa[b]naphthalene; 17) was synthesized via interception of the heterocyclic ortho ‐quinodimethane 15 with l‐bromo‐2‐chlorocyclopropene, followed by aromatization of the adduct 16 with t‐BuOK.
Rh(II)‐Catalyzed Isomerizations of Cyclopropenes Evidence for Rh(II)‐Complexed Vinylcarbene Intermediates
Authors: Müller Paul , Pautex Nicole , Doyle Michael P. , Bagheri Vahid 
Published: December 2004

AbstractThe thermocatalytic rearrangements of cyclopropenes 1‐4 have been investigated in the presence of Rh(IT) perfiuorobutyrate. 1, 2, 3‐Triphenylcyclopropene (1a) undergoes rearrangement lo diphenylindene 5a or, with alkoxycyclopropene derivatives, to α, β‐unsaturated ketone 6. Furan formation occurs with 2, 3‐diphenylcyclo‐propenecarboxylate 2, but the diethyl counterpart 3 rearranges to dienoate 8. 2‐Alkylcyclopropenecarboxylates 4 afforded (E)‐methylidenecyclopentane derivatives 9 as the only isolable product in yields of ca. 35 %. A mechanism involving regio‐ and stereospecific cyclopropene ring opening to a Rh‐complexed vinylcarbene and insertion of the latter into the CH bond to give 9 is proposed. An analogous mechanism should account for the rearrangement products of 1 to 3.
Isolation and Characterization of s̀‐Adducts upon Attempted Vicarious Nucleophilic Substitution with Cationic Arene‐Iron Complexes
Authors: Müller Paul , Bernardinelli Gérald , Motallebi Shahrokh 
Published: December 2004

AbstractReaction of the carbanions derived from chloromethyl phenyl sulfone or 1 ‐chloroethyl phenyl sulfone with the cationic [Fe(arene)Cp] complexes 8 or 9 produced isolable c‐adducts 10‐12. Attempted base induced elimination of the s̀‐adducts, which would have led to products of vicarious nucleophilic substitution (VNS reaction), failed. Similarly, no VNS products were obtained, when the (arene)tricarbonylchromium complexes 4 were reacted with the anion of chloromethyl phenyl sulfone.
Synthesis of All Four Stereoisomers of (E)‐Vitamin KT (Phylloquinone), Analysis of Their Diastereoisomeric and Enantiomeric Purities and Determination of Their Biopotencies
Authors: Schmida Rudolf , Antoulas Syméon , Rüttimann August , Schmid Max , Vecchi Max , Weiserb Harald 
Published: December 2004

AbstractAll four stereoisomers of (E)‐vitamin Kb i. e. (21E, 7R, 111R)‐l (= 1a), (21E, 71 R, l11S)‐1 (= 1b), (21E, 71 S, 111S) 1 ( = 1c), and (21E, 71S, 111R)‐l ( = Id), have been synthesized in a state of high chemical and stereoisomeric purity. The synthesis of stereoisomers lb‐d relied on the use of the optically active Cf1* and C*10‐building blocks (R)‐ or (S)‐4‐(benzyloxy)‐3‐methylbutanal ((R)‐ or (S)‐2) and (R)‐ or (S)‐citronellal ((R)‐ or (S)‐3) which had been secured by the Rh1‐catalyzed allylamine‐to‐enamine isomerization technology. For the synthesis of the natural (E)‐vitamin‐K1 stereoisomer 1a, a new route starting from natural phylol was developed, based on an O‐alkylation/rearrangement procedure. A HPLC method was developed which separates with remarkable efficiency all four stereoisomers of (E)‐ as well as three out of the four stereoisomers of (Z)‐vitamin K1 on optically active poly(trityl methacrylate) as the chiral stationary phase supported on Nucleosil. By this method, the stereoisomeric content of the stereoisomers 1b‐d synthesized was shown to be in the range of 96‐98 %, while the natural isomer 1a was configurationally uniform. The biological activity of the four (E)‐vitamin‐K1 stereoisomers was determined by means of the curative prothrombin time test with vitamin‐K‐depleted chicks. A high precision of the results was obtained with the recently introduced up‐and‐down organization of the test and the statistical evaluation according to an estimation procedure. With the natural (E)‐vitamin‐K1 stereoisomer 1a as standard (set at 1. 0), activities of 0. 93, 1. 19, and 0. 99 were found for stereoisomers 1b, 1c, and 1d, respectively. Within the confidence limits, these activity ratios can be regarded as identical, A very similar efficacy was obtained by comparison of (E, all‐rac )‐vitamin K1 ((21E, RS, 11′ RS)‐1; equimolar mixture of the four stereoisomers 1a‐d) with the natural (E)‐vitamin‐K1 stereoisomer 1a). A synergistic effect was not detectable, as was the case with the eight α‐tocopheryl‐acetate stereoisomers.
Ringerweiterungen und Ringverengungen bei der Umsetzung von 1, 3‐Oxazolidin‐2, 4‐dionen und 1, 3‐Thiazoiidin‐2, 4‐dion mit 3‐Amino‐2H‐azirinen
Authors: Ametamey Simon M. , Heimgartner Heinz 
Published: December 2004

Ring Enlargements and Ring Contractions in the Reaction of 1, 3‐Oxazolidine‐2, 4‐diones and l, 3‐Thiazolidine‐2, 4‐dione with 3‐Amino‐2H‐azirinesThe reaction of 3‐amino‐2H‐azirines 1 and 1, 3‐oxazolidine‐2, 4‐diones 2 in MeCN at room temperature leads to 3, 4‐dihydro‐3‐(2‐hydroxyacetyl)‐2H‐imidazol‐2‐ones 3 in good yield (Scheme 2, Table 1). A reaction mechanism proceeding via ring enlargement of the bicyclic zwitterion A to give B, followed by transannular ring contraction to C, is proposed for the formation of 3. This mechanism is in accordance with the result of the reaction of 2a and the 15N‐labelled 1a*: in the isolated product 3a*, only N(3) is labelled (Scheme 1). The analogous reaction of 1 and 1, 3‐thiazolidine‐2, 4‐dione (5) is more complex (Schemes 4 and 5, Table 2). Besides the expected 3, 4‐dihydro‐3‐(2‐mercaptoacetyl)‐2H‐imidazol‐2‐ones 7, 5‐amino‐3, 4‐dihydro‐2H‐imidazol‐2‐ones of type 8 and/or N‐(1, 4‐thiazin‐2‐ylidene)ureas 9 are formed. In the case of 2‐(dimethylamino)‐1‐azaspiro[2. 3]hex‐1‐ene (1d), the postulated eight‐membered intermediate 6d could be isolated. Its structure as well as that of 9f has been determined by X‐ray structure analysis. A reaction mechanism for the formation of the 1, 4‐thiazine derivatives of type 9 is proposed in Scheme 6.
Chemie von α‐Aminonitrilen. Aziridin‐2‐carbonitril photochemische Bildung aus 2‐Aminopropennitril
Authors: Drenkard Susanne , Ferris James , Eschenmoser Albert 
Published: December 2004

AbstractThe English Footnotes (*) referring to Schemes 1‐6 are intended to provide an extension of this summary. In the Footnote (*) to Scheme 5, a definition of the term ‘chirogenic reaction step’ is given.2‐Aminopropenenitrile in solvents such as MeCN, MeOH, or H2O is photoisomerized by UV light to racemic aziridine‐2‐carbonitrile (rac‐2); the larger part of the starting material, however, fragments to HCN and MeCN. The observed photocyclization constitutes a structural connection within an ensemble of C3H4N2 compounds considered to be potentially relevant to prebiotic chemistry.
Synthese von Pyrano[3,2‐b][1]benzopyranen aus 1‐Nitroglycalen
Authors: Brade Walter , Vasella Andrea 
Published: December 2004

Synthesis of Pyranol [3,2‐b][1]benzopyrans from 1‐NitroglycalsA synthesis of pyrano[3,2‐b][l]benzopyrans β‐addition of salicylic aldehyde to 1‐nitroglycals, followed by a Henry reaction, is described. This sequence gave the cis‐annelated pyranobenzopyranes 9 and 11 from 5 in 54 and 9% yield, respectively, demonstrating the pronounced diastereoselectivity of the β‐addition. Reductive denitration of the crude product mixture yielded 14(75%), 15(15%), and 16(7%), which were oxidized to the aryl ketones 20 and 21, respectively. Reduction of 20 (NaBH4) gave exclusively 15. The ketone 20 was deprotected to 22 and 23.
5‐Methylnaioxone and 5‐Methylnaltrexone: Synthesis and Pharmacological Evaluation
Authors: Schmidhammer Helmut , Mayer‐Valkanover Karin , Walla‐Kugler Michaela 
Published: December 2004

AbstractStarting from 5‐methyl‐oxycodone (6), 5‐methylnaloxone (4), and 5‐methylnaltrexone (5) have been prepared in several steps. Both 4 and 5 behaved as partial agonists in the AcOH writhing agonism and antagonism test in mice.
Weitere Beiträge zur Synthese von (+)‐Aspicilin
Authors: Quinkert Gerhard , Döller Uwe , Eichhorn Mathias , Küber Frank , Nestler Hans Peter , Becker Heinrich , Bats Jan W. , Zimmermann Gottfried , Dürner Gerd 
Published: December 2004

Further Contributions to the Synthesis of (+)‐AspicilinThere are two reasons to try to find out. whether the initial and final parts of the ‘photochemical synthesis’ of the 18‐membered lichen macrolide (+)‐aspicilin (5a) can be improved (cf. Schemes 1 and 2). This synthesis acts as an indicator for the utility of the earlier introduced photolactonization and as a source of large‐ring‐sized lactones, objects for computer‐assisted conformational analysis.
Segregation of Charge in Ions of Dibenzo[a,c]naphthacene: Relation of Topology and Electronic Structure. An NMR, ESR, and ENDOR Study
Authors: Cohen Yoram , Fraenkel Yigal , Rabinovitz Mordecai , Felder Patrick , Gerson Fabian 
Published: December 2004

Abstract1H‐ and 13C‐chemical shifts of the dianion of dibenzo[a,c]naphthacene (1) have unambiguously been assigned by 2D‐NMR spectroscopy. They indicate a remarkable charge distribution, as most of the negative charge is localized on the ‘anthracenic’ moiety, while the ‘phenanthrenic’ moiety is almost neutral. Association of 12− with alkali‐metal counterions has only a minor effect on the chemical shifts. The charge partitioning in 12−, which is reproduced by ωβ calculations in the frame of the Hückel model, must, thus, be considered as an intrinsic property of the 4nπ‐electron system of 12−. It is rationalized in terms of differing energy contents of the constituent anthracenic and phenanthrenic moieties. ESR and ENDOR studies of the radical anion 1\documentclass{article}\pagestyle{empty}\begin{document}$ 1^{\scriptstyle {{\relbar}\kern-4pt {.} }} $\end{document} and the radical cation 1\documentclass{article}\pagestyle{empty}\begin{document}$ 1^{+ \atop \dot{}} $\end{document} show that the π‐charge distribution in 12− is reflected by the π‐spin distributions in the two radical ions of the alternant hydrocarbon 1.
Photo‐oxygenation of Styrenic Estrogens: Structural Analysis of 8,9‐Didehydro‐, 6,7‐Didehydro‐, and 9,11‐Didehydroestrone Derivatives and Their Reactivity towards Singlet Oxygen
Authors: Malet Carles , Planas Antoni , Brosa Carme , Piniella Juan F. , Rius Jordi 
Published: December 2004

AbstractA series of didehydro‐3‐O‐methyl‐estrones having a styrenic framework, with the ring‐A‐conjugated double bond in all three possible positions (8,9‐didehydro‐ (6),9,11‐didehydro‐ (1b), 6,7‐didehydro‐ (9), and the 12,18‐di‐nor‐8,9‐didehydroestrone analog 11), were compared for their reactivity towards singlet oxygen. Under dye‐sensitized photo‐oxygenation conditions, both, products derived from ene‐type reactions with the isolation of a stable hydroperoxide and a fragmentation product, were obtained from 6 (see Scheme 3), while only fragmentation took place for 1b (Scheme 1), Kinetic studies indicated that 6 is more reactive towards 1O2 than 1b (β = 9.2·10−3 mol·1−1 vs 3.3·10−2 mol·1−1, resp.). The observed reactivity, apparently, does not match with ene‐type reaction and [2 + 2]cycloaddition being in competition, since the most activated substrate 6 preferentially yields ene‐type products and their derivatives. Conformational analysis on the structure of 6 and 1b, both calculated by molecular‐mechanic techniques (MMPMI) and determined by X‐ray diffraction, show that the allylic H‐atoms satisfy the orthogonality rule for ene‐type reactions. The product distribution is best rationalized by applying Fukui's rule which takes into account a combination of electronic and geometric factors. Substrates 9 and 11 yielded photo‐products arising from ene‐type reaction with no stable primary products isolated (Scheme 4). Geometric considerations based on the calculated structures by molecular mechanics are consistent with the observed results.
Synthesis, structure, and reactivity of secosteroids containing a medium‐sized ring. Part 32. Conformations and photochemical reactivity of some unsaturated 5,10‐secosteroidal ketones
Authors: Lorenc Ljubinka , Pavlović Vladimir , Mihailović Mihailo Lj. , Kalvoda Jaroslav , Fuhrer Hermann 
Published: December 2004

AbstractUV irradiation of the unsaturated (E)‐5,10‐secosteroidal ketones 1 and 6 results, in addition to (E/Z)‐isomeri‐zation, in an intramolecular Pateino‐Büchi reaction and, in the case of 1, in transannular cyclization (along with AcOH elimination). The stereochemistry of the observed intramolecular photoprocesses can be explained in terms of ground‐state conformations of the (E)‐seco‐ketones 1 and 6 in solution.
Fluxional Behaviour of Isocyanide Derivatives of Dodecacarbonyltetrairidium
Authors: Orlandi Alessandra , Ros Renzo , Roulet Raymond 
Published: December 2004

AbstractThe fluxional behaviour of [Ir4(CO)11(t‐BuNC)] (1) and [Ir4(CO)11(ArNC)] (Ar = 4‐methoxyphenyl, 4‐tolyl, phenyl, 4‐chlorophenyl, 4‐nitrophenyl; 2–5) has been investigated by 2D and variable‐temperature 13C‐NMR. These techniques give new evidence of the processes responsible for CO exchange, namely two successive merry‐go‐rounds causing Cotton‐like scrambling and a CO rotation about one metal center.
2D‐NMR ConformationaL Studies of ChiraL Functionalized Ferrocenylphosphine Ligands for the Gold(I)‐Catalyzed Aldol Reaction
Authors: Togni Antonio , Blumer Ruth K. , Pregosin Paul S. 
Published: December 2004

AbstractThe conformations in solution of six selected chiral 1,1′‐bis (diphenylphosphino)ferrocenyl ligands bearing functionalized side chains, the diastercoisomers 4 and 5 and 6–9, have been elucidated by 2D‐NMR methods (COSY, TOCSY, NOESY, and 1H,31P and 1H,13C correlations). The possible relationship between the preferred conformation and the stereoselectivity observed in the gold(I)‐catalyzed asymmetric aldol condensation in the presence of these ligands is discussed.
Über Pterinchemie. 90. Mitteilung. Synthese und Kristallstruktur des ersten chinoiden Dihydropterinmolybdän (IV)‐Komplexes
Authors: Fischer Berthold , Strähle Joachim , Viscoittinf Max 
Published: December 2004

Synthesis and Crystal Structure of the First Quinoid Dihydropterinmolybdenum (IV) ComplexThe first molybdenum(IV) complex with a quinoid dihydropterin, i.e. 2, was isolated and characterized by IR, UV and NMR data and single‐crystal X‐ray diffraction. The reaction of MoVIO2Cl2 with the biologically important 6β‐5,6,7,8‐tetrahydro‐L‐biopterin(2) (7) in MeOH gave almost quantitatively trichloro(1,5‐quinoid‐7,8‐dihydro‐6H‐L‐biopterin)oxomolybdenLim(IV) (2). The complex crystallizes with one molecule of MeOH in the noncentrosymmetric orthorhombic space group P212121 (No. 19) with unit cell dimensions a = 1009.3(3), b = 1104.7(3), and c = 1484.5(4) pm and Z = 4. The Mo‐atom has a distorted octahedral geometry (Fig.1). It is coordinated by N(5) and O(4) of the pterin ligand. The distance of the Mo–N(5) bond (202 pm) is unusually short compared to similar complexes. O(4) is located trans to a terminal oxo ligand. The octahedral coordination is completed by three Cl‐atoms in a meridional arrangement. Complex 2, with the Mo‐atom in the enzyme‐relevant oxidation state +IV and the pterin in the intermediate quinoid dihydro form, should lead to an extension of the proposed ‘common molybdenum cofactor’ model.
Deoxy‐nitrosugars. 17th communication. Synthesis of ketose‐derived nucleosides from 1‐deoxy‐1‐nitroribose
Authors: Mahmood Khalid , Vasella Andrea , Bernet Bruno 
Published: December 2004

AbstractA new approach to ketose‐derived nucteosides is described. It is based upon a chain elongation of 1‐deoxy‐1‐nitroaldoses, followed by activation of the nitro group as a leaving group, and introduction of a pyrimidine or purine base. Thus, the nitroaldose 7 was prepared from 3 by pivaloylation (→4), synthesis of the anomeric nitrones 5/6, and ozonolysis of 6 (Scheme 1). Partial hydrolysis of 4 yielded 8/9, which were characterized as the acetates 10/11 and transformed into the nitrones 12/13. Ozonolysis of 12/13 gave 14/15, which were acetylated to 16/17. Henry reaction of 7 lead to 19 and 20, which were acetylated to 21 and 22 (Scheme 2). Michael addition of 7 to acrylonitrile and to methyl propynoate yielded the anomers 23/24 and 25/26, respectively. Similar reactions of 16/17 were prevented by a facile β‐elimination. Therefore, the nitrodiol 15 was transformed into the orthoesters 27 and then, by Henry reaction, partial hydrolysis, and acetylation, into 28 and 29 (Scheme 2). The structure of 19 was established by X‐ray analysis. It was the major product of the kinetically controlled Henry reaction of 7. Similarly, the β‐D‐configurated nitroaldoses 23 and 25 were the major products of the Michael addition. This indicates a preferred ‘endo’‐attack on the nitronate anion derived from 7. AMI calculations for this anion indicate a strong pyramidalization at C(1), in agreement with an ‘endo’‐attack. Nucleosidation of 21 by 31 afforded 32 and 33. Yields depended strongly upon the nature and the amount of the promoter and reached 77% for 33, which was transformed into 34, 35, and the known ‘psicouridine’ (36; Scheme 3). To probe the mechanism, the trityl‐protected 30 was nucleosidated yielding 37, or 37 and 38, depending upon the amount of FeCl3. Nucleosidation of the nitroacetate 28 was more difficult, required SnCl2 as a promoter, and yielded 39 and 40. The β‐D‐anomer 40 was transformed into 36. Nucleosidation of 23 (SnCl4) yielded the anomers 41 and 42, which were transformed into 43 and 44, and hence into 45 and 46 (Scheme 4). Similarly, nucleosidation of 25 yielded 47 and 48, which were deprotected to 49 and 50, respectively. The nucleoside 49 was saponified to 51. Nucleosidation of 21 by 52 (SnCl2) afforded the adenine nucleosides 53 and 54 (Scheme 5). The adenine nucleoside 53 was deprotected (→55→56) to ‘psicofuranine’ (1), which was also obtained from 58, formed along with 57 by nucleosidation of 28. The structure and particularly the conformation of the nitroaldoses, nitroketoses, and nucleosides are examined.
Caro‐Cryptands: Tris‐carotenoid macrobicyclic ligands–synthesis, crystal structure, and dinuclear copper(I) complexes
Authors: Lehn Jean‐Marie , Vigneron Jean‐Pierre , Bkouche‐Waksman Itka , Guilhem Jean , Pascard Claudine 
Published: December 2004

AbstractThe tris‐carotenoid macrobicycles 1 and 2 were obtained in good yields in a one‐step macrobicyclisation condensation between the tripode N(CH2CH2NH2)3 and the polyolefinic dialdehydes 5 and 6. They form dinuclear cryptates by complexation of two CuI ions. The crystal structure of the tris‐carotenoid compound 2 confirms that it contains three parallel polyolefinic strands. These substances may formally be considered as prototypes of molecular ‘cables’ formed by three electron‐conducting molecular wires.
A New Synthesis of Coprine and O‐Ethylcoprine
Authors: Kienzler Thomas , Strazewski Peter , Tamm Christoph 
Published: December 2004

AbstractCoprine (1), a toxine of the mushroom Coprinus atramentarius, was synthesized starting from the 2‐amino and 1‐carboxy‐protected L‐glutamic acids 4 and 12. Compound 4 was first decarboxylated by a radical chain reaction to bromide 5 which underwent ring closure to cyclopropanecarboxylate 6 on treatment with NaH (Scheme 1). Subsequent oxidative electrolysis of 7 to form tert‐butyl N‐(1‐ethoxycyclopropyl)carbamate (8) and acidic hydrolysis yielded the 1‐aminocyclopropanol hydrochloride (9). Selective cleavage of the amino‐protecting group of 8 (→ 10 or 11), coupling of the corresponding amine 13 with L‐glutamic acid 12, and acidic hydrolysis of the resulting L‐glutamine derivative 17 yielded O‐ethylcoprine (3) and coprine (1).
Studies on the Enzymatic Acylation of Quinic Acid, Shikimic Acid, Shikimic Acid, and Their Derivatives in Organic Solvents
Authors: Danieli Bruno , De Bellis Paolo , Barzaghi Laura , Carrea Giacomo , Ottolina Gianluca , Riva Sergio 
Published: December 2004

AbstractQuinic acid (1a), shikimic acid (2), and their derivatives were acylated in organic solvents by several lipases and by the protease subtilisin Carlsberg. The most satisfactory results were obtained with methyl (or benzyl) quinate (7a (or 8a)) and lipase from Chromobacterium viscosum adsorbed on Celite, which showed an overshelming preference towards the acylation of OH–C(4). Under optimized conditions, the syntehtically useful 4‐O ‐acetylquinate 8d was isolated in ca. 90% yield. On the other hand, acylation of methyl shikimate (10a) showed no regioselectivity with any of the enzymes tested. A possible rationale for the different behavior of Chromobacterium viscosum lipase towards 7a and 10a is given, comparing the conformations of these two molecules, as deducted from 1H‐NMR and molecular‐mechanics calculation.