Helvetica Chimica Acta

doi: 10.1002/hlca.19910740401pmid: N/A

Warmutha, Ralf; Grell, Ernst; Lehn, Jean‐Marie; Bats, Jan W.; Quinkert, Gerhard

doi: 10.1002/hlca.19910740402pmid: N/A

The four photo‐cleavable ligands 1–4 of the macrobicyclic‐cryptand type have been synthesized by introducing a photo‐sensitive 2‐nitrobenzyl‐ or 4,5‐dimethoxy‐2‐nitrobenzyl‐ether bond into one of the bridges. These compounds are expected to retain the selective binding features of the parent cryptands and to allow the photolytically induced release of alkali ions in aqueous solution. The crystal structures of the ligand 5‐(2‐nitro‐phenyl)‐4,7,13,16,21,24‐hexaoxa‐1,10‐diazabicyclo[8.8.8]hexacosane (3) and of its KSCN complex 13 have been determined. They are analogous to those of the corresponding parent species, confirming the macrobicyclic geometry and the cryptate nature of the complex. Spectroscopic properties are reported.

Wessel, Hans Peter; Englert, Gerhard; Stangier, Peter

doi: 10.1002/hlca.19910740403pmid: N/A

Two symmetrical trehalose glycosyl ‘acceptors’ 4 and 6 were prepared and three of the unsymmetrical type, 8, 10, and 11. Glucosylation of symmetrical ‘acceptor’ 4 gave a higher yield of trisaccharide (44%) than protect ve‐group manipulation, namely via selective debenzylidenation 2 → 9 or monoacetylation 2 → 5 which proceeded in moderate yields (33–34%). A comparison of catalysts in the cis‐glucosylation of trehalose ‘acceptor’ 10 with tetra‐O‐benzyl‐β‐D‐glucopyranosyl fluoride 13 profiled triflic anhydride ((Tf)2O) as a new reactive promoter yielding 92% of trisaccharide 14, deblocking gave the target saccharide α‐D‐glucopyranosyI‐(1 → 4)‐α,α‐D‐trehalose. 1H‐NMR spectra of most compounds were analyzed extensively. The use of the ID TOCSY technique is advocated for its time efficiency, if needed supplemented by ROESY experiments.

Färber, Gerald; Keller, Walter; Kratky, Christoph; Jaun, Berhard; Pfaltz, Andreas; Spinner, Christoh; Kobelt, André; Eschenmoser, Albert

doi: 10.1002/hlca.19910740404pmid: N/A

The structure of a derivative of coenzyme F430 from methanogenic bacteria, the bromide salt of 12,13‐diepi‐F430 pentamethyl ester (5, X = Br), was determined by X‐ray structure analysis. It reveals a more pronounced saddle‐shaped out‐of‐plane deformation of the macrocycle than any hydroporphinoid Ni complex investigated so far. The crystal structure confirms the constitution proposed for coenzyme F430 (2) and shows that in the epimer 5, the three stereogenic centers in ring D, C(17), C(18), and C(19), have the (17S)‐, (18S)‐, and (19R)‐configuration, respectively. Deuteration and 2D‐NMR studies independently demonstrate that native coenzyme F430 (2) has the same configuration in ring D as the epimer 5. Therefore, our original tentative assignment of configuration at C(19) and C(18) [1] has to be reversed. This completes the assignment of configuration for all stereogenic centers in coenzyme F430, which has the structure shown in Formula 2.

Bolm, Carsten; Weickhardt, Konrad; Zehnder, Margareta; Glasmacher, Dorothea

doi: 10.1002/hlca.19910740405pmid: N/A

The synthesis of the complexes 3 of various metals ligated to chiral 4,5‐dihydro‐2‐(2′‐oxidophenyl‐ϰO)oxazoles‐ϰN is described (Scheme). Three of them, i.e. 3a, 3e, and 3f containing CuII, ZnII and NiII, respectively, were analyzed by X‐ray diffraction studies. A series of CuII complexes (6a–d) with differently substituted dihydrooxazoles have been synthesized.

Pindur, Ulf; Otto, Christian; Molinier, Michel; Massa, Werner

doi: 10.1002/hlca.19910740406pmid: N/A

Diels‐Alder reactions of the (1H‐indol‐3‐yl)‐enacetamides and ‐endiacetamides 1a–d with some carbodieno‐philes and 4‐phenyl‐3H‐1,2,4‐triazole‐3,5(4H)‐dione give rise to the novel amino‐functionalized carbazole; 4–6 and 8 (Scheme 3). Ethenetetracarbonitrile reacts with 1b to furnish the Michael‐type adduct 7 (Scheme 3). Structural aspects of the starting materials 1, which exhibit above all 3‐vinyl‐1H‐indole reactivity, are discussed with regard to the prediction of a Diels‐Alder process.

Duh, Jauh‐Lin; Bobst, Albert M.

doi: 10.1002/hlca.19910740407pmid: N/A

Oligothymidylates (oligo(dT)'s) with the sequence‐specifically‐incorporated one‐atom‐tethered C(5)‐nitio‐xide‐labeled nucleoside 1 were synthesized by the phosphotriester method. Some modifications of the protocol were required to account for the chemical reactivity of the nitroxide, the stability of which was monitored during the synthesis by electron paramagnetic resonance (EPR) spectroscopy. The EPR specific activity (AEPR) of the FPLC‐purified nitroxide‐labeled oligomers was determined and found to be in agreement with enzymatically prepared spin‐labeled nucleic acids. Annealing the nitroxide‐labeled oligo(dT)'s to (dA)n or oligo(dA) resulted in different EPR‐lineshape changes suggesting a strong coupling of the short‐tethered nitroxide to global macro‐molecular motion.

Rosemeyer, Helmut; Seela, Frank

doi: 10.1002/hlca.19910740408pmid: N/A

1‐(2′‐Deoxy‐β‐D‐threo‐pentofuranosyl)thymine (= 1‐(2′‐deoxy‐β‐D‐xylofuranosyl)thymine; xTd; 2) was converted into its phosphonate 3b as well as its 2‐cyanoethyl phosphoramidite 3c. Both compounds were used for solid‐phase synthesis of d[(xT)12‐T] (5), representing the first DNA fragment build up from 3′–5′‐linked 2′‐deoxy‐‐β‐D‐xylonucleosides. Moreover, xTd was introduced into the innermost part of the self‐complementary dodecamer d(G‐T‐A‐G‐A‐A‐xT‐xT‐C‐T‐A‐C)2 (9). The CD spectrum of d[(xT)12–T] (5) exhibits reversed Cotton effects compared to d(T12) (6; see Fig. 1), implying a left‐handed single strand. With d(A12) (7) it could be hybridized to form a propably Left‐handed double strand d(A12) · d[(xT)12–T] (7·5) which was confirmed by melting experiments in combination with temperature‐dependent CD spectroscopy. While 5 was hydrolyzed by snake‐venom phosphodiesterase, it was resistant towards calf‐spleen phosphodiesterase. The modified, self‐complementary duplex 9 was hydrolyzed completely by snake‐venom phosphodiesterase, at a twelvefold slower rate compared to unmodified 8; calf‐spleen phosphodiesterase hydrolyzed 9 only partially.

Yu, Qian‐sheng; Liu, Chi; Brzostowska, Margareth; Chrisey, Linda; Brossi, Arnold; Greig, Nigel H.; Atack, John R.; Soncrant, Timothy T.; Rapoport, Stanley I.; Radunz, Hans‐Eckart

doi: 10.1002/hlca.19910740409

Muller, Marc; Bur, Daniel; Tschamber, Théophile; Streith, Jacques

doi: 10.1002/hlca.19910740410pmid: N/A

The ketene derivative of the chiral oxazolidinone 1 underwent non‐concerted stereo specific [2 + 2] cycloadditions with the (Z)‐imine moiety of diazepines 2, leading thereby with good diastereoselection to the trans‐β‐lactam adducts 3 (major) and 4 (minor). The absolute configuration of the major cycloadduct 3a was determined by an X‐ray analysis. Its formation is discussed in terms of minimisation of steric interaction in the two transition states which give sequencially the zwitterionic intermediates and the final cycloadducts.