Acta chemica Scandinavica. Series B: Organic chemistry and biochemistry最新文献

D.c. polarography of 2-amino-6-chloropurine in aqueous medium over a broad pH range revealed two diffusion waves, the first of which corresponds to reduction of the C(6)-Cl bond, leading to formation of 2-aminopurine in high yield. Condensation of the sodium salt of 2-aminopurine with (2-acetoxyethoxy)methyl chloride led to the two isomeric 9- and 7-(2-hydroxyethoxymethyl)-2-aminopurines. The 9- isomer, 6-deoxyacyclovir, a prodrug of acyclovir previously synthesized by another route, was readily converted to the latter by xanthine oxidase; the 7-isomer was not a substrate. The intense fluorescence of 6-deoxyacyclovir makes it a convenient fluorescent substrate for xanthine oxidase, although less sensitive than xanthine; it is shown that 2-aminopurine would be a very sensitive fluorescent substrate. The polarographic behaviour of the riboside of 2-amino-6-chloropurine was virtually identical with that of the parent purine, leading to a simple procedure for conversion of 2-amino-6-chloropurine nucleosides and acyclonucleosides to the corresponding 2-aminopurine congeners.

In a vesicle preparation from rat cerebral cortex, carbachol recognizes a high-affinity and a low-affinity muscarinic agonist binding site. A number of agents, including veratridine (10 microM), gramicidin (10 microM) and valinomycin (10 microM), which depolarize the vesicles also appear to block the high-affinity muscarinic agonist binding site. Lowering [Na+] (from 137 to 80 mM) or raising [K+] (from 5 to 50 mM) produced effects similar to those of the depolarizing agents. Agents such as tetrodotoxin (1 microM), which block the Na+-channel, also appear to block the high-affinity agonist binding site or to convert it into a low-affinity agonist binding form.

The crystal and molecular structures of the alpha- and beta-L-Asp isomers of L-aspartyl-L-alanine have been determined at 120 K using 1226 and 1609 reflections (I greater than 2.5 sigma I), respectively. The space group for the alpha-isomer is P2(1), with cell parameters a = 4.788(1), b = 16.943(4), c = 5.807(1) A and beta = 107.55(2) degrees; final R factor 0.042. The space group for the beta-isomer is P2(1)2(1)2(1) with a = 4.845(1), b = 9.409(2) and c = 19.170(3) A; final R-factor 0.047. The two peptides crystallize as zwitterions with the side-chain acidic groups ionized. Each molecule adopts a trans configuration at the peptide bond with both carboxyl groups situated on the same side of the peptide plane. The geometries of the aspartyl moieties do, however, differ in the two structures. The peptide bond is significantly longer in the beta-isomer than in the alpha-isomer, with C-N 1.344(3) and 1.328(4) A, respectively. A very short intermolecular carboxyl...carboxyl hydrogen bond (O...O = 2.502(4) A) is observed in the crystals of the alpha-isomer.

The eight possible monodeoxy derivatives of methyl beta-maltoside and two bisdeoxy derivatives have been synthesized. The unprotected glycosides have all been investigated by NMR (1H and 13C) spectroscopy in order to confirm their structures and to obtain supporting information about their preferred solution conformations. The compounds have all been tested as substrates toward the hydrolase, amyloglucosidase (AMG) and it has been demonstrated that three hydroxy groups (3, 4' and 6') are essential for the compounds to act as substrate for the enzyme. The kinetic parameters KM (Michaelis-Menten constant) and VM (maximum rate for the reaction) have been determined using 1H NMR spectroscopy at 500 MHz.

The structure of the calcium channel modulator isopropyl 4-(2,1,3-benzoxadiazol-4-yl)-1,4-dihydro-2,6-dimethyl-5-nitro- 3-pyridinecarboxylate has been determined by X-ray analysis. Structural and stereochemical features are discussed in relation to previously determined structures of calcium agonists and antagonists of the 1,4-dihydropyridine type, and in relation to a newly proposed model for the dihydropyridine binding site.