The high binding affinity and specificity of antibodies for a wide range of ligands has recently been exploited in the generation of catalysts for acyl-transfer reactions, carbon-carbon bond forming and carbon-carbon bond cleaving reactions. In addition, a number of strategies are emerging for the generation of catalytic antibodies including transition state stabilization, catalysis by approximation, and the introduction of catalytic groups or cofactors into antibody combining sites. An important goal in the design of catalytic antibodies is the development of general rules relating hapten structure to the corresponding catalytic groups in the antibody combining site. We report here that electrostatic interactions between a hapten and the complementary antibody can be exploited to generate catalytic amino-acid side chains in an antibody-combining site. The antibody-catalysed reaction, a beta-elimination reaction, exhibits saturation kinetics, substrate specificity, competitive inhibition by hapten, and specific inactivation by a reagent that modifies carboxylate residues.

4841Scheme I11 0 intermediate. Although nargenicin bears little structural resemblance to erythromycin, a consideration of the biosynthetic origins of each of these metabolites would indicate several close parallels in the elaboration of the parent polyketide chain. In order to probe these apparent biosynthetic similarities, we have investigated the incorporation of (2S,3R)-[ 2,3-'3Cz]-2-methyl-3-hydroxypntanoyl NAC-thioester (1)6 into nargenicin.Ten 70-mL fermentation cultures of Nocardia agentinesis Huang ATCC 3 1306 were incubated in 500-mL flasks at 30 OC and 250 rpmsx8 for 24 h before administration of a total of 40 mg of [2,3-13C2]-1 dissolved in 5 mL of 20% ethanol. Additional quantities of precursor were added after 48 h (20 mg) and 72 h (40 mg). After 96 h, the resulting crude nargenicin was extracted with ethyl acetate and purified by a combination of flash column chromatography and preparative TLC on silica gel. The 100.6 MHz I3C N M R spectrum of the labeled nargenicin A, (7.1 mg) displayed the predicted set of enhanced and coupled doublets (Jcc = 36.2 Hz, 0.2 atom% enrichment), centered at 32.76 and 78.79 ppm, corresponding to C-16 and C-17, respecti~ely.~ The observation of coupled I3C N M R signals establishes the intact incorporation of the labeled thioester 1 into nargenicin, indicating that the polyketide synthetase of N . argenfinesis can utilize a partially elaborated intermediate of the chain elongation process. These results are consistent with a chain elongation scheme involving adjustment of functionality and stereochemistry of the growing polyketide chain prior to each condensation reaction. The observed incorporation of the (2S,3R)-enantiomer of 1 is expected based on the previously determined absolute configuration of nargeni~in.~ Incorporation experiments involving more advanced intermediates of the chain-elongation process are in progress.(6) The preparation of 1 was carried out by using the methods of Evans' for the erythroselective construction of aldol intermediates. Thus [2'-"C]-

Supplementary Material Available: Figures showing atomic numbering scheme and packing within the unit cell; tables of atomic positional and thermal parameters, intramolecular bond lengths and angles, least squares planes, interplanar angles, and angles about tungsten (5 pages); tables of structure factors (11 pages). Ordering information is given on any current masthead page.(18) The formation of aniline and C02 after partial hydrolysis of 3 was confirmed by NMR (aniline) and GC (CG2) analysis of a sample in acetone-(f6.

No abstract

A monoclonal antibody (mAb), designated 15D8, was produced from BALB/c splenocytes of mice injected with Escherichiu coli flagella. ELISA of motile cells, non-motile cells and partially purified flagellin proteins showed that the mAb reacted specifically with flagella of E coli and with other members of the family Enterobacteriaceae. Western immunoblot analyses of enterobacterial flagella or cell extracts demonstrated that the antibody reacted with a single protein species in the extracts which was identical in size to purified flagellin. The antigenic determinant for this antibody appears to be surface exposed and linear in configuration, since the antibody reacted with native flagella and flagella which had been denatured. This antibody was also used to demonstrate that although the flagella proteins are heterogeneous in size, at least one epitope is highly conserved.