bluuebunny/crossref_metadata_2025_split huggingface dataset:
Zur Energiedelle von Diradikalen, VII. Konjugativ stabilisierte Trimethylenmethan‐Derivate. Geometrieabhängigkeit der Singulett‐Triplett‐Aufspaltung
Authors: Roth Wolfgang R. , Winzer Markus , Korell Michael , Wildt Holger 
Published: July 2007

Energy Well of Diradicals, VII. – Conjugative‐Stabilized Trimethylenemethane Derivatives. Geometry Dependence of the Singlet‐Triplet SplittingFor the three 2,1′‐bis‐allyl diradicals 3–5 the singlet‐triplet splitting has been determined by the oxygen‐trapping technique. In agreement with theory the value for the planar diradical is large (>14 kcal · mol−1) whereas for the orthogonal geometry the energy gap is small (6.3 kcal · mol−1). In all cases a triplet groundstate is observed. From the rotational barrier of the exo methylene groups in 6 it is shown that the interconversion of the planar and orthogonal singlet states have activation barriers (6–9 kcal mol−1) which are responsible for their kinetic stability. In contrast to 6, where the formation of the orthogonal diradical proceeds by way of the planar diradical 3, the formation of the analogous orthogonal diradical 29 from homofulvene 17 is a concerted process. This difference is an important observation with respect to the fundamental understanding of concerted and non‐concerted reactions.
Synthesis of pyruvated saccharide fragments related to the aggregation factor of the marine sponge Microciona prolifera
Authors: Ziegler Thomas 
Published: July 2007

AbstractTreatment of phenyl 2,3,6,2′,3′‐penta‐O‐benzoyl‐1‐thio‐β‐D‐lactoside (7) with BF3 in methyl pyruvate afforded the corresponding phenyl 4′,6′‐O‐[(R)‐1‐(methoxycarbonyl)ethylidene]‐1‐thio‐β‐D‐lactoside (9) in 91% yield. The latter was converted via bromide 10 into the corresponding lactal 11 the azidonitration of which afforded an unseparable mixture of the „gluco”︁‐ and „manno”︁‐configurated azido nitrates 12 (97%). As an alternative, benzyl O‐(β‐D‐galactopyrnosyl)‐(1→4)‐2‐azido‐2‐deoxy‐α‐D‐glucopyranoside (15) was prepared in two steps and 91% yield from the corresponding fully acetylated 2‐azido‐2‐deoxylactosyl bromide 13 and was further modified in four steps to give the benzoylated benzyl 4′,6′‐O‐benzylidene‐2‐deoxy‐2‐[(2,2,2‐trichloroethoxycarbonyl)amino]‐α‐D‐lactoside 18 in 78% overall yield. The benzylidene acetal of the latter was cleaved to give the diol 19 the pyruvation of which as for compound 9 afforded the corresponding pyruvated lactosamine derivative 20 (81%). Hydrogenolysis of 20 followed by treatment with trichloroacetonitrile gave the corresponding pyruvated disaccharide trichloroacetimidate 22 (77%). Coupling of the latter with Z‐protected 5‐amino‐1‐pentanol followed by deblocking of the intermediates furnished 5‐aminopentyl 2‐acetamido‐4′,6′‐O‐[(R)‐1‐carboxyethylidene]‐2‐deoxy‐β‐D‐lactoside (2). Similarly, condensation of 22 with 5‐[(benzyloxycarbonyl)amino]‐pentyl 2,4‐di‐O‐benzyl‐β‐L‐fucopyranoside (25) followed by deblocking of the intermediate trisaccharide afforded 5‐aminopentyl O‐{4,6‐O‐[(R)‐1‐carboxyethylidene]‐β‐D‐galactopyranosyl}‐(1→4)‐2‐acetamido‐2‐deoxy‐β‐D‐glucopyranoside‐(1→3)‐β‐L‐fucopyranoside (3). Saccharides 2 and 3, represent fragments of the Microciona prolifera aggregation factor.
Medium‐sized cyclophanes, 37. [n.2]metacyclophanediquinones: Synthesis, conformational studies and reduction to tetrahydroxy[n.2]metacyclophanes
Authors: Yamato Takehiko , Matsumoto Jun‐Ichi , Sato Mitsuhiro , Noda Kozo , Moriguchi Tetsuji , Tashiro Masashi 
Published: July 2007

AbstractThe title compounds, [n.2]metacyclophanediquinones 6a‐f, were prepared by oxidation of the corresponding di‐tert‐butyldihydroxy[n.2]metacyclophanes 5a‐f with Tl(OCOCF3)3 in CF3COOH. When [n.2]quinonophanes 6a‐e were reduced with Zn powder in acetic acid, the corresponding tetrahydroxy derivatives 8a‐e were obtained, which were converted to the tetraacetates 9a‐e. The solution conformations of diquinones 6a‐f and tetrahydroxy[n.2]MCPs 8a‐e are sensitive to the chain length of the bridges. The ring inversion barriers determined by variable‐temperature 1H‐NMR spectroscopy decrease with increasing length of the bridges. In addition, a solvent effect on the ratio of anti to syn conformers was found to occur in tetrahydroxy[6.2]metacyclophane 8d and dihydroxy[6.2]metacyclophanes 5d, 10d, and 12d. The conformationally rigid tetraacetoxy[n.2]metacyclophanes 9 exhibit fixed „anti”︁ and „syn”︁ conformations. The anti and syn ratio is strongly governed by the number of methylene bridges. Thus, a anti‐to‐syn ratio of the tetraacetoxy[5.2]‐ (9c) and ‐[6.2]metacyclophane (9d) differing from that of the tetraols 8c and 8d was obtained. This difference is due to the ring inversion of 8c and 8d. The assignment of anti and syn conformations was confirmed by 1H‐NMR analyses. The dynamics of the ring inversion is also discussed.
Liquid crystals derived from carbohydrates: Synthesis and properties of oxadecaline compounds
Authors: Vill Volkmar , Tunger Hanns‐Walter 
Published: July 2007

AbstractReaction of glucal 1 with alkoxybenzene leads after hydrogenation and deacetylation to β‐C glycosides 4, which can be used as chiral compounds in the synthesis of chiral calamitic liquid crystals. The combination with aliphatic aldehydes leads to liquid crystals 5 showing a monotropic SA phase, with aromatic p‐alkoxy‐substituted aldehydes to compounds 6 with enantiotropic cholesteric and SA phases. Reaction with p‐alkoxy‐substituted phenylboronic acids gives liquid crystals 7 forming SA and ferroelectric SC* phases. They all exhibit a high twisting power and blue phases in contact preparation.
Stereo‐ and regioselective intramolecular heck reaction of α‐amino acid derivatives for the synthesis of enantiopure 3,4‐dihydroisoquinolinones
Authors: Tietze Lutz F. , Burkhardt Olaf 
Published: July 2007

AbstractAcylation of the alkenes 1a–d and 3, easily prepared from the corresponding α‐amino acids, with 2‐iodobenzoyl chloride gives 2a–d and 4 which cyclize to the enantiopure dihydroisoquinolinones 5a–d and 9, resp., in an intramolecular Heck reaction using 5 mol‐ % of Pd(OAc)2 in the presence of PPh3, TPAB, and KOAc with excellent diastereoselectivity.
Diastereo‐ and enantioselective synthesis of the 18‐membered lichen macrolide (+)‐aspicilin
Authors: Enders Dieter , Prokopenko Oleg F. 
Published: July 2007

AbstractThe asymmetric synthesis of the lichen macrolide (+)‐aspicilin (1) was realised in 19 steps and with high stereoselectivity (de ≥ 91 %, ee ≥ 96%). Three of the four stereogenic centres were generated by employing the SAMP/RAMP hydrazone method. Key steps of the synthesis are the α,α′‐double alkylation of RAMP hydrazone (R)‐10 of 2,2‐dimethyl‐1,3‐dioxan‐5‐one B and the enantioselective synthesis of the bromo alcohol (S)‐9 (subunit A) by a combination of SAMP hydrazone α‐alkylation with subsequent Baeyer‐Villiger oxidation.
On the preparation of β‐amino acids from α‐amino acids using the Arndt‐Eistert reaction: Scope, limitations and stereoselectivity. Application to carbohydrate peptidation. Stereoselective α‐alkylations of some β‐amino acids
Authors: Podlech Joachim , Seebach Dieter 
Published: July 2007

AbstractThe Arndt‐Eistert homologation of α‐amino acids was studied to determine the stereoselectivity in this reaction by chromatographic up‐to‐date analytical methods. While carba‐mate‐protected phenylglycine was transformed to the corresponding β‐amino acid methyl ester with a stereoselectivity of only 9:1, all other tested amino acid derivatives (Ala, Phe, Ser, Orn, tert‐Leu and perhydro‐azepine‐2‐carboxylic acid, suitably protected) were homologated with full retention of configuration (products 9–17). The intermediate diazo ketones 1–8 were purified and characterized by their NMR spectra. When nucleophiles derived from partially protected sugars were present during decomposition of the diazo ketones (derived from amino acids or dipeptides), a strong dependence of the yield (products 21–24) on the degree of steric hindrance of the nucleophilic OH group was observed. Two of the β‐amino acids obtained from the homologation reaction were transformed to α‐substituted (25–27, 31, 32) and α,α‐disubstituted β‐amino acid derivatives (28, 29) with excellent selectivities (in most cases, a single diastereoisomer was obtained).
Synthesis of phthalocyanines with one sulfonic acid, carboxylic acid, or amino group
Authors: Kliesch Holger , Weitemeyer Andrea , Müller Silke , Wöhrle Dieter 
Published: July 2007

AbstractMonofunctional phthalocyanines7a,b, one bearing a sulfo and the other one a carboxyl group, were synthesized by lithium alkoxyde‐catalyzed statistical tetramerization of 4‐(4‐tert‐butylphenoxy)‐1,2‐benzenedicarbonitrile (3c) with 1,2‐dicyanobenzenes3a,bcarrying a carboxyl or sulfo group. Tribenzonaphthoporphyrazines9a,bwith one carboxyl or amino group were prepared under similar reaction conditions by tetramerization of 3,6‐dihexyloxy‐1,2‐benzenedicar‐bonitrile with 6‐amino‐ or 6‐carboxy‐2,3‐naphthalenedicar‐bonitrile6b,6a. The zinc(II)‐containing macrocycles7a, b, 9a, bobtained in yields of 11–20% were purified by column chromatography and characterized by UV/Vis, mass, and1H‐NMR spectroscopy.
Bimolecular formation of radicals by hydrogen transfer, 9. Uncatalyzed transfer hydrogenation of α‐methylstyrene by 9,10‐dihydroacridine and N‐methyl‐9,10‐dihydroacridine
Authors: Friebolin Heike , Rüchardt Christoph 
Published: July 2007

AbstractHydrogen is transferred from acridane (1c) and N‐methylacridane (1d) to α‐methyl‐styrene (2) in a bimolecular uncatalyzed reaction at 260–300°C. On the basis of the activation parameters (for 1c: ΔH≠ = 29.0 kcal/mol, ΔS≠ = −23.5 e.u. in triglyme) the kinetic isotope effect (kH/kD = 2.0, in triglyme at 300°C) as well as the small solvent effects and from the observation of an EPR signal of N‐methylhydroacridyl radicals a three‐step radical mechanism is prosposed which is initiated by a retrodisproportionation between 1 and 2.
Enantioselective reformatsky reaction of methyl bromodifluoroacetate
Authors: Braun Manfred , Vonderhagen Anja , Waldmüller Delia 
Published: July 2007

AbstractThe Reformatsky reagent 2 generated from methyl bromodifluoroacetate is added to benzaldehyde in the presence of carbinols 3a, b, amino alcohols 3c‐g, or amino alkoxide 3h. N‐Methylephedrine 3c provides the highest enantioselectivity in the formation of the adduct S‐4a (84% ee; >96% after recrystallization) whose absolute configuration is determined by an X‐ray structural analysis of the amide 6.
Glycolipids from sponges, I. Glycosyl ceramide composition of the marine sponge Agelas clathrodes
Authors: Costantino Valeria , Fattorusso Ernesto , Mangoni Alfonso 
Published: July 2007

AbstractThe marine sponge Agelas clathrodes was analyzed for gly‐cosphingolipids, and four cerebrosides (1a‐4a) were isolated, each as a mixture of homologs. The structure of the new glycosphingolipid 1a was elucidated by extensive NMR studies of its peracetate and by chemical analysis. The presence of unusual α‐glycosphingolipids in sponges of the genus Agelas was confirmed.
Glycolipids from sponges, II. Glycosyl ceramide composition of the marine sponge Agelas longissima
Authors: Cafieri Francesco , Fattorusso Ernesto , Mangoni Alfonso , Taglialatela‐Scafati Orazio 
Published: July 2007

AbstractA specimen of the marine sponge Agelas longissima was analyzed for glycosphingolipids. Three cerebrosides 1a‐3a were isolated, each as a mixture of homologs. The structure of the new glycosphingolipid 1a was elucidated by extensive NMR studies of its peracetate derivative and chemical analysis. Compound 2a, previously isolated from another specimen of A. longissima, exhibits in the new specimen a remarkably different alkyl chain composition.
Ozonolyses of O‐methyloximes in the presence of acid derivatives: A new access to substituted ozonides
Authors: Griesbaum Karl , Övez Bikem , Huh Tae Sung , Dong Yuxiang 
Published: July 2007

AbstractOzonolyses of O‐methyloximes (4) of 5‐, 6‐ and 7‐membered cycloketones in the presence of esters of trifluoroacetic acid (5) or of acyl cyanides (6) afforded ozonides of types 7 and 8, respectively, which are formally derived from vinyl ethers or vinyl cyanides. Similarly, ozonolysis of the O‐methylated oxime of acetone (9) in the presence of esters of trifluoroacetic acid (5) and of the O‐methylated oxime of 2‐naphthaldehyde (11) in the presence of acyl cyanides (6) gave the corresponding ozonides of types 10 and 12, respectively.
Pyridinium N‐phenoxide betaines and their application to the characterization of solvent polarities, XXI Determination of new and corrections of old ET(30) values as empirical measures of solvent polarity for 40 organic solvents
Authors: Reichardt Christian , Schäfer Gerhard 
Published: July 2007

AbstractBy means of the negative solvatochromic betaine dyes 1a and 1b empirical solvent polarity parameters ET(30) for 40 organic solvents of current interest were newly determined or corrected (Table 1).
Functional dyes for molecular switching. Dihydroazulene/vinylheptafulvene photochromism: Effect of π‐arylenes on the switching behavior
Authors: Spreitzer Hubert , Daub Jörg 
Published: July 2007

AbstractThe reversible interconversion of dihydroazulene (DHA) and vinylheptafulvene (VHF) can be utilized to switch a number of physical properties. This communication reports on a fluorescent switch. By a multistep sequence involving an [8 + 2] cycloaddition route 9‐anthracenyl‐1,4‐phenylene was covalently attached to C‐2 of the DHA chromophore affording DHA‐1 which undergoes complete and clean photochemical ring opening to vinylheptafulvene VHF‐1. The latter is thermally reverted to DHA‐1. The kinetics and the energetics of the thermal back reaction are discussed. On/off switching of luminescence was investigated: DHA‐1 displays fluorescence whereas VHF‐1 is nonfluorescent at ambient temperature.
Structure‐odor relationships of sandalwood odorants: Synthesis of (Z)‐7‐oxa‐β‐santalol
Authors: Buchbauer Gerhard , Lebada Philippine , Spreitzer Helmut , Wolschann Peter 
Published: July 2007

AbstractBy means of a convergent synthesis strategy, the title substance (Z)‐7‐oxa‐β‐santalol (4) was prepared starting with the side chain synthon 5‐iodo‐2‐methyl‐2‐pentenylmethoxyethoxymethyl ether (7) and the bicyclic synthon ethyl 3‐methylene‐7‐oxabicyclo[2.2.1]hept‐5‐ene‐2‐carboxylate (5). The new santalol analogue 4 is odorless, although the steric requirements for the sandalwood odor are met. The reasons for this are discussed.
Norpinyl‐norbornyl rearrangements: Destabilized 2‐norpinyl cations
Authors: Fendel Wolfgang , Kautz Cornelia Brigitte , Kirmse Wolfgang , Klar Matthias , Siegfried Rainer , Wonner Aribert 
Published: July 2007

AbstractIn order to explore the effect of electron‐withdrawing substituents on 2‐norpinyl (bicyclo[3.1.1]hept‐2‐yl)→2‐norbornyl (bicyclo[2.2.1]hept‐2‐yl) rearrangements, cyano and penta‐fluoroethyl groups were introduced into the α and β (= bridgehead) positions. The substrates were synthesized from norpinan‐2‐one (8) by addition of HCN or C2F5Li, from 2‐aminonorbornane‐2‐carbonitrile (25) by rearrangement, and from 1‐(pentafluoroethyl)bicyclo[2.1.1]hexan‐2‐one (51) by ring expansion. Arenesulfonates and diazonium ions were used to generate the 2‐norpinyl cations. – Electron acceptors in the α position of 2‐norpinyl substrates promote the norpinyl→norbornyl rearrangement. Internal return of the counterion leads to endo‐2‐norbornyl sulfonates, often without formation of the analogous alcohols, i.e., the destabilized norpinyl cations do not escape from tight ion pairs. Electron acceptors in the β (bridgehead) position favor displacement and elimination processes with retention of the norpinyl structure while the norpinylnorbornyl rearrangement is inhibited, more strongly by β‐C2F5 than by β‐CN. The tendency to separate the positive charge from the electron acceptor explains the divergent effects of α and β substitution. – The kH/kα‐CN and kH/kβ‐CN rate ratios in the 2‐norpinyl and 2‐norbornyl series are virtually the same, and the stereoselectivity of the intervening carbocations is not significantly affected by electron‐withdrawing substituents.
Prearranged glycosides, 2. Intramolecular glycosylation of prearranged saccharides as a novel strategy for the construction of β‐L‐rhamnosidic linkages
Authors: Lau Richard , Schüle Gunter , Schwaneberg Ulrich , Ziegler Thomas 
Published: July 2007

AbstractDisaccharides containing a β‐L‐rhamnosyl residue were prepared by a novel intramolecular glycosylation strategy. Thus, suitably benzyl‐protected L‐rhamnosyl donors (ethyl and phenyl 1‐thiorhamnoside 7, 18) were prearranged in positions 2 and 3 with benzyl 2‐O‐benzoyl‐4,6‐O‐benzylidene‐α‐D‐glucopyranoside 8 in position 3 by a malonyl, succinyl and phthaloyl bridge, respectively, to give the corresponding connected saccharides 9, 12, 16 and 20. After regioselective opening of the benzylidene ring of the glucoside residue to give compounds 10, 13, 17 and 21, the latter afforded the 3,2′‐ and 3,3′‐bridged disaccharides 22–25 upon intramolecular glycosylation with a thiophilic reagent. The anomeric selectivity of this intramolecular glycosylation is strongly influenced by the nature of the alkanoyl and aroyl bridge, its position at the rhamnosyl residue and the solvent used for the coupling. Best results were obtained in acetonitrile with the succinyl „spacer”︁ attached to position 2 of the phenyl 1‐thiorhamnoside and position 3 of the glucoside that afforded the corresponding β‐(1→4)‐linked disaccharide 22β in 76% yield.
Diterpenoid total synthesis, XXXI. Synthesis and absolute configuration of (−)‐stypoldione, a metabolite of Stypopodium zonale
Authors: Mori Kenji , Koga Yasuo 
Published: July 2007

Abstract(S)‐3‐Hydroxy‐2,2‐dimethylcyclohexanone (2) was converted to (−)‐stypoldione (1), the ichthyotoxic and cytotoxic metabolite of the brown alga Stypopodium zonale. The present synthesis established the absolute configuration of (−)‐stypoldione as depicted in 1.
Syntheses and CD studies of new cholesteno[4,3‐d]‐ and ‐[7,6‐d]pyrimidines
Authors: Hasan Mashooda , Rashid Naghmana , Khan Khalid Mohammed , Perveen Shahnaz , Snatzke Günter , Duddeck Helmut , Voelter Wolfgang 
Published: July 2007

AbstractThe syntheses of 5α‐ and 5β‐cholest‐3‐eno[4,3‐d]pyrimidines (7) and (7′) could be achieved by using the hydroxymethylene derivative of cholestan‐4‐one (5) prepared from cholesterol (1). Their 2′‐derivatives 7a‐7d and 7′a‐7′c were also synthesized. 5α‐Cholest‐6‐eno[7,6‐d]pyrimidine (13) was prepared by the reaction of 5α‐cholestan‐7‐one (12) with tris‐(formylamino)methane. The CD spectra exhibit at least three Cotton effects between 300 and 210 nm, a first CD band around 290, a second one around 260, and a third one around 220 nm. An earlier developed quadrant rule can be applied to the determination of the sign of the first CD band, while the suggested helicity rule allows prediction of the third CD band.
Tricarbonylmethane acylhydrazones: Reactions under acylating conditions and formation of fused isoxazole derivatives with concomitant NN bond cleavage
Authors: Somogyi László , Sohár Pál 
Published: July 2007

AbstractReactivity of 3‐(1‐acylhydrazonoethyl)‐2H‐pyran‐2‐ones 1a–k and 4a–d towards various acetylating agents and nitrous acid, respectively, is studied. Treatment of dehydroacetic acid (DHA) (thio)acylhydrazones 1a, c, f with Ac2O/Et3N afforded the 3‐(1‐triacetylhydrazinoethenyl) derivative 3a. The analogous coumarin derivative 5 was obtained by treatment of acetylhydrazone 4a with AcCl/PhNMe2. With concomitant N–N bond cleavage acylhydrazones 1c–f were converted to the pyrano‐isoxazole 6 by treatment with NaNO2/AcOH whereas coumarin derivative 4d was converted to the imine 4e.
Unusual reactions between chloroketenes and 1,3,5‐tri‐tert‐butylcyclopentadiene
Authors: Dehmlow Eckehard Volker , Bollmann Christof , Neumann Beate , Stammler Hans‐Georg 
Published: July 2007

AbstractReaction of title compound 1 with dichloroketene resulted in a complex rearrangement to 2 when the ketene was generated from Cl3CCOCl/Zn. In contrast, treatment of 1 with the ketene produced from dichloroacetyl chloride/triethylamine gave a bicyclo[3.2.0]heptenone (3) along with acylation product 4. Reaction of monochloroketene with 1 afforded the „normal”︁ endo‐chloro compound 6 which thermally rearranged to the formal Diels‐Alder product 7.
Molecular switches: Calculations on the stereodivergent hetero Diels‐Alder reaction of chiral 1‐oxa‐1,3‐butadienes with different lewis acids
Authors: Tietze Lutz F. , Schulz Gerhard 
Published: July 2007

AbstractThe stereodivergent facial differentiation of the intermolecular hetero Diels‐Alder reaction of the 1‐oxa‐1,3‐butadiene 1 with 2 in the presence of trimethylsilyl trifluoromethanesulfonate (TMS‐OTf) or Me2AlCl is explained on the basis of semiempirical calculations (AM1 and PM3). The oxabutadiene 9 was shown to prefer the anti arrangement of the carbonyl groups of the imide moiety in the ground state by 1.8 kcal/mol (Am1) or 2.2 kcal/mol (PM3). In the silylated compound 10 this preference is even more pronounced. In contrast, in the chelate 11 the imide moiety is fixed in a syn conformation. The orientation of the oxazolidinone rings in 10 and 11 is opposite: thus, the absolute configuration of the cycloadducts is determined by a facial differentiation due to an asymmetric induction under chelate control (11) or nonchelate control (10).
A photochemical route to vinylglycine and a vinylglycine dipeptide
Authors: Griesbeck Axel G. , Hirt Joachim 
Published: July 2007

AbstractEnantiomerically pure vinylglycine (4b) can be prepared from natural („chiral pool”︁) amino acids by photoelimination of γ‐functionalized N‐phthaloyl amino acid esters. Two routes have been developed: (a) a three‐step synthesis of substrate 3b [PhtN‐Met(SO)OMe] from (S)‐methionine and subsequent photolysis, (b) the use of N‐phthaloyl activated methyl 2‐amino‐4‐chloro‐ or ‐4‐bromobutanoates 3d, e which are available from (S)‐methionine (four‐step synthesis) or from (S)‐homoserine (two‐step synthesis). The photoelimination (of HOSMe from 3b and of HX from 3d, e) proceeds quantitatively and leads to N,C‐protected vinylglycine 4a in high yields. This strategy could also be applied to peptide‐bound substrates as was shown for the protected Met‐Gly (5b) which was transformed into the N‐protected vinylglycine‐glycine dipeptide 6 in three steps.
Synthesis of optically active α,β‐disubstituted β‐amino nitriles and β‐amino acids starting from asparagine
Authors: Gmeiner Peter , Hummel Evi , Haubmann Christian 
Published: July 2007

AbstractStarting from the enantiomerically pure building block 2 which is readily available from D‐asparagine α,β‐disubstituted β‐amino nitriles and β‐amino acids could be synthesized. After deprotonation of the nitrile α‐position the introduction of substituents was performed by alkylation of either 2 or the TBDMS‐protected derivative 3. Starting from the β homoserine equivalent 2 the reaction proceeds via a dianionic intermediate resulting in a preferred formation of the threo‐configured products 6a,b (ratio of isomers: 7:1). Modification of the side chain was demonstrated by displacement reactions with LiBH4 or potassium thioacetate.
Enzymes in organic synthesis. Expedient enantioselective synthesis of (S)‐(−)‐3,4‐dihydroxybutylphosphonate, an isosteric substrate mimic for glycerol phosphate oxidase
Authors: Arth Hans‐Lothar , Sinerius Gudrun , Fessner Wolf‐Dieter 
Published: July 2007

AbstractThe title compound (S)‐(−)‐2 was obtained in enantiomerically pure form and 47% overall yield starting from (S)‐malic acid (S)‐7 by a 5‐step sequence involving reduction to (S)‐1,2,4‐butanetriol (S)‐8, acetalization, and introduction of the phosphonate group by an Arbusow reaction. Compound (S)‐(−)‐2 is a substrate for the L‐glycerol 3‐phosphate oxidase from Pediococcus sp. which quantitatively converts it into 4‐hydroxy‐3‐oxobutylphosphonate 4, an isosteric analog of dihydroxyacetone phosphate. Kinetic constants of the latter reaction were determined.