The initial discovery by Hinckley1 of the effectiveness of the dipyridine adduct of the rare earth complex tris(dipivalomethanato)europium(III) [Eu(DPM)3 • 2py]

We have prepared a series of cis-4-(tetrazolylakyl)piperidine-2-carboxylic acids as potent and selective N-methyl-D-aspartic acid (NMDA) receptor antagonists. NMDA antagonists may prove to be useful therapeutic agents, for instance, as anticonvulsants, in the treatment of neurodegenerative disorders such as Alzheimer's disease and in the prevention of neuronal damage that occurs during cerebral ischemia. The compounds prepared were evaluated in vitro in both receptor binding assays [( 3H]CGS-19755, [3H]AMPA, and [3H]kainic acid) and in a cortical-wedge preparation (versus NMDA, quisqualic acid, and kainic acid) to determine affinity, potency, and selectivity. The new amino acids were also evaluated in vivo for their ability to block NMDA-induced convulsions in neonatal rats and NMDA-induced lethality in mice. The most potent compound of this series, 15 (LY233053), selectively displaced [3H]CGS-19755 binding with an IC50 of 107 +/- 7 nM and selectively antagonized responses due to NMDA in a cortical-wedge preparation with an IC50 of 4.2 +/- 0.4 microM. Compound 15 blocked both NMDA-induced convulsions in neonatal rats (minimum effective dose (MED) = 20 mg/kg ip) and NMDA-induced lethality in mice (MED = 5 mg/kg ip). This is the first example of an NMDA receptor antagonist that incorporates a tetrazole moiety as an omega-acid bioisostere. These amino acid antagonists are also unique from their phosphonic acid counterparts in that they have a shorter duration of action in vivo. For the treatment of acute disorders such as stroke, where an NMDA antagonist would be administered parenterally, the shorter duration of action may be beneficial, e.g., allowing for better dosage control. The combination of potent NMDA receptor antagonism and a short duration of action may make these compounds useful therapeutic agents in the treatment of a variety of neurological disorders.

The biosynthetic origin of antibiotic A10255 was investigated using 14C-and 13C-labeled amino acids. DL-[l-13C]Serine labeled 15 of the 17 amino acid residues present in A10255G. These included the oxazole, thiazole, dehydroalanine, masked glycine, masked alanine and pyridine moieties. The same 15 residues labeled by serine were labeled by [2-13C]glycine, apparently by conversion of the glycine to [2,3-13C]serine. Formation of the pyridine ring occurred via a C3 to C3 condensation of two serines. The results indicated origin of the masked alanine from alanine; the masked glycine from glycine; the thiazole residues from cysteine; and the threonine, masked dehydrobutyrine, masked dehydronorvaline and masked dehydroleucine residues from threonine. L-[CH3-13C]Methionine labeled the methyl carbon of the masked dehydronorvaline moiety in factor B and the two methyl carbons of the masked dehydroleucine moiety in factor E. The results demonstrate that A10255 originates exclusively from amino acids in a mannersimilar to the closely related thiopeptide antibiotics nosiheptide and thiostrepton.

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A new cepham metabolite has been isolated from the filtered broth of Cephalosporium acremonium by high performance liquid chromatography (HPLC) and identified as 7ß-(5-Damino-adipamido)-3ß-hydroxy-3a-methyl-cepham-4a-carboxylic acid (I). Pure penicillin N was prepared using HPLC in the analytical mode. When I was added in place of penicillin N as substrate for the cell-free biosynthetic of cephalosporin, no formation of deacetoxycephalosporin C (II) was observed.A synthetic cepham derivative, 7ß-(5-D-aminoadipamido)-3-exomethylene-cepham-4a-carboxylic acid (III) was also tested in the cell-free system as a possible intermediate. The compound III was shown to be an inhibitor of the ring expansion enzyme that converts penicillin N to deacetoxycephalosporin C.We have shown earlier3) that using HPLC one can isolate metabolites directly from the fermentation broth.Modification of appropriate stationary, and liquid phases, employed in the course of that first investigation, led to the isolation1)of new tripeptides from the broth of P. chrysogenum (Fig. 1).When the same system was applied to the present investigation of the broth of C. acremonium (Fig. 2), a new cepham derivative (I) was obtained.Its structure was suggestive of a possible relationship to deacetoxycephalosporin C (DAC, deacetoxy ceph C) (II) and, therefore, we examined its role in biosynthesis of DAC in a cell-free system derived from C. acremonium.KOHSAKA and DEMAIN4) were first to describe a cell-free system from C. acremonium CW-19 that converted penicillin N into a penicillinase-resistant cephalosporinase-sensitive material. YOSHIDA et al.,5) have shown this compound to be II by paper electrophoresis and paper and TLC chromatography.More recently, in another cell-free system derived from C. acremonium mutant M-0198, this finding was further confirmed6) using the same HPLC system we introduced in the examination of the broth of C. acremonium.3) In all these experiments however impure penicillin N was used as the substrate for the cell-free synthesis of DAC. We are able to prepare essentially pure penicillin N for use in the cellfree experiment.The process of the ring expansion from penicillin N to DAC was followed by injection into the HPLC system of aliquots of 50 microliters of the reaction mixture. The UV absorbance profile at 254 nm of authentic DAC was compared to profiles obtained from aliquots of the reaction mixture observed at 0 time, then at 20-minute intervals after addition of penicillin N to a total of 60 minutes. At that