An NMR study of the Lythraceae alkaloids

Abstract

Several Lythraceae alkaloids containing either a trans-fused (decinine, decodine, decaline) or a cis-fused (decamine, verticillatine, vertaline) quinolizidine ring system were examined by high-field NMR spectroscopy. Oneand two-dimensional NMR techniques were used in order to assign the 1 H and 13 C chemical shifts. The selective 1-D TOCSY experiment was particularly helpful for resolving the 1 H signals of the quinolizidine ring of some of the alkaloids. The chemical shift data combined with two-dimensional NOE experiments differentiated the cis-and transquinolizidine rings and provided structural information that correlated well with structures derived from molecular modelling.

Total Synthesis of (±)-Decinine via an Oxidative Biaryl Coupling with Defined Axial Chirality

“…Thus, lactone 27 was subjected to Pd-catalyzed hydrogenation in ethyl acetate to give (±)-decinine 1 in 80% yield (Scheme ). The NMR data for the synthesized decinine ( 1 ) were identical to the data reported for material isolated from natural sources …”

“…The NMR data for the synthesized decinine (1) were identical to the data reported for material isolated from natural sources. 23 In summary, we have achieved for the first time the total synthesis of racemic decinine (1) over a nine-step linear sequence in an overall yield of 4.7%. The key steps in the sequence were the VOF 3 -mediated oxidative biaryl coupling and the gold-catalyzed annulation.…”

Biphenylquinolizidine Alkaloids from Lagerstroemia indica

“…The 25 carbons present in the 13 C NMR spectrum (Table ) comprised one O -methyl, eight methylene, eight methine, and eight quaternary carbons by using a DEPT experiment. Nine resonances [δ C 19.0 (CH 2 , C-8), 25.7 (CH 2 , C-7), 26.2 (CH 2 , C-6), 34.5 (CH 2 , C-4), 38.8 (CH 2 , C-2), 47.8 (CH, C-1), 50.1 (CH 2 , C-9), 57.3 (CH, C-5), 71.1 (CH, C-3)] in the 13 C NMR spectrum seemed to be due to a cis -fused quinolizidine ring, as observed in decamine . The downfield aliphatic carbons at δ C 47.8, 50.1, and 57.3 indicated an adjacent nitrogen atom.…”

“…Comparison of the 1 H and 13 C NMR data of 2 with those of 1 inferred that 2 was an analogue of 1 with a variation in the quinolizidine ring (Table ). Nine resonances [δ C 24.8 (CH 2 , C-7), 26.2 (CH 2 , C-8), 33.5 (CH 2 , C-6), 37.4 (CH 2 , C-4), 39.1 (CH 2 , C-2), 52.9 (CH 2 , C-9), 59.6 (CH, C-1), 59.7 (CH, C-5), 70.7 (CH, C-3)] in the 13 C NMR seemed to be due to a trans -fused quinolizidine ring, as observed in decinine . The downfield proton H-1 at δ H 2.99 showed the same HMBC correlations with C-9 (δ C 52.9), C-5 (δ C 59.7), C-3 (δ C 70.7), C-24 (δ C 114.4), C-20 (δ C 126.0), C-25 (δ C 136.6), and C-23 (δ C 146.6) as those of 1 , indicating the attachment of an aromatic ring at C-1.…”

Indolizidine and quinolizidine alkaloids

“…Full 1 H and 13 C NMR spectra have now been reported for these six alkaloids, and all signals have been assigned with the aid of various one-and two-dimensional experiments, with 1-D TOCSY and 2-D NOESY spectra providing valuable structural information. 75 Characteristic and diagnostically useful differences in chemical shift for the trans-and cis-fused alkaloids were identified. In addition, a reasonable correlation was found between the observed NOE interactions and proton distances determined by means of molecular modelling.…”