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The relative magnitudes of the chemical shift differences (Deltadeltas) in the two diastereomers of menthyl esters of known chiral derivatizing agents (CDAs) were compared to those of the alpha-methoxy-alpha-trifluoromethyl-1-naphthylacetyl (MTN((1))A) analogues I. Discrimination of the terminal diastereotopic methyl resonances in esters of the homologous, symmetrical carbinols II was evaluated. Remarkably, the methyls differed in the MTN((1))A esters III even when n = 15; an unexpected crossover in the sign of the Deltadelta values was also observed.

Asymmetric aldol reactions were conducted with the titanium enolate of N(3)-hydrocinnamoyl-3,4,5,6-tetrahydro-2H-1,3,4-oxadiazin-2-one to afford aldol adducts 5a-j. The dominant product of the asymmetric aldol reaction was the non-Evans syn adduct as determined by (1)H NMR spectroscopy and X-ray crystallography. When evaluating the (1)H NMR spectra of adducts 5a-j, a highly shielded signal with an average chemical shift of 0.05 ppm was observed. This signal was readily determined to be the C(5)-methyl group of the oxadiazinone. It is presumed that the overall conformation adopted by the aldol adducts in solution places an aromatic ring of the N(3)-substituent in close proximity to the C(5)-methyl group. An investigation of this conformational preference is conducted employing (1)H NMR spectroscopy, X-ray crystallography, and computational methods.

Three new cyclic heptapeptides, cyclomarins A−C (1−3), were isolated from extracts of a cultured marine bacterium collected in the vicinity of San Diego, CA. The major metabolite, cyclomarin A (1), contains three common and four unusual (or unique) amino acids. The structures of the new metabolites were determined using 1D and 2D NMR methods, and the stereochemistry was determined from an X-ray crystal structure of the diacetate derivative of 1. Cyclomarin A (1) displays significant antiinflammatory activity in both in vivo and in vitro assays.

Three novel sesterterpenes, neomangicols A−C (1−3) were isolated from the mycelial extract of a marine fungus belonging within the genus Fusarium. The carbon skeleton of the neomangicols is undescribed and constitutes a new class of C25 rearranged sesterterpenes. The structures of the new metabolites were determined by 1D and 2D NMR methods, and the absolute configuration of 3 was determined by Mosher ester analysis of a diacetonide derivative. The configurations of the three stereocenters in the side-chain were assigned on the basis of molecular modeling and NOESY NMR correlations observed for several diacetonide derivatives of 3. Neomangicols A and B are cytotoxic against HCT-116 human colon carcinoma in in vitro evaluation, while neomangicol B inhibits the growth of the Gram-positive bacterium Bacillus subtilus with a potency similar to that of the antibiotic gentamycin.

Mosher's MTPA (methoxy(trifluoromethyl)phenylacetyl) technology is applied to the assignment of absolute configuration of several synthetic and natural chiral amines. The substrates are cyclic, secondary amines. The resulting amides usually contain significant populations of two rotamers, readily distinguished by 1H NMR spectroscopy. Thus, two complementary sets of Δδ values are obtained from a single analysis, thereby enhancing the power of the method. A strategy for the MTPA derivatization of (the N-methyl tertiary amine in) the tropane alkaloid, cocaine, is also described. The exceptionally large Δδ values observed for these MTPA amides make this a valuable and reliable method for assignment of amine configuration (even in some cases where only one diastereomeric MTPA amide is readily available).

Mosher's MTPA (methoxy(trifluoromethyl)phenylacetyl) technology is a well-known tool used to determine the absolute configuration of chiral alcohols and primary amines. The technique now has been extended to include secondary amines. A number of MTPA amide derivatives have been prepared from cyclic amines. Both piperidines and pyrrolidines have been studied. A detailed discussion of the conformational issues associated with both amide bond rotation and ring flipping is presented. The observed 1H NMR chemical shifts are correlated into a model that allows unambiguous determination of absolute configuration of cyclic secondary amines. While the presence of amide rotamers must be accounted for in the analysis, this is a relatively straightforward process that follows from detailed evaluation of coupling constant data and is often aided by COSY. The exceptionally large Δδ values observed for these MTPA amides make this a valuable and reliable method for assigning amine configuration.