First Direct and Detailed Stereochemical Analysis of Strictosidine

Abstract

Using the easy lactamization of vincoside (4), epimer-free strictosidine (1) was prepared from secologanin (2) and tryptamine (3). 2D NMR methods were used to determine unambiguously the 1H- and 13C-NMR chemical shifts, the 1H−H and 13C−1H coupling constants, and the 1H−1H NOE interactions in strictosidine (1). A minimal number of spectroscopic parameters (11 coupling constants, 3 NOEs) and some theoretical considerations have made it possible to select the single species of the 648 selected stereoisomers and to confirm directly the S configuration at the newly formed C-3 chiral center, the P helicity of the dihydropyran and tetrahydropyridine rings, and the conformations around C-14 and the glycosidic bridge.

Metabolite Diversity in Alkaloid Biosynthesis: A Multilane (Diastereomer) Highway for Camptothecin Synthesis in Camptotheca acuminata

“…These coupling constants ( 1 J C-H ) were 170 Hz for isomer 2 and 178 Hz for isomer 3, the largest isomer-related difference among all 1 J C-H values and consistent with two epimers differing in the stereochemistry of C-glycosylation at position 21 ( Figure 3, Table 2). Based on similarities to NMR spectra reported for 21(S)-strictosidine, we assign strictosidinic acid isomer 3 to have the 21(R) configuration and strictosidinic acid isomer 2 to have 21(S) configuration (Figure 3), the latter being in common with the published structure and coupling constants of 21(S)-strictosidine (Patthy-Lukáts et al, 1997). NMR data for stereocenters at positions 3, 15, and 20 and the carbohydrate resonances for isomers 2 and 3 did not differ substantially, consistent with the difference being the configuration at position 21.…”

Monoterpenoid indole alkaloids from Alstonia rostrata

“…Hence, configurations of alstrostines C-E were same to akummicine, as shown in Fig. 1 12 with exception for additional methylene (δ C 55.7, t) and methoxycarbonyl [δ C 172.9 (s) and 51.8 (q)] in 4. In the HMBC spectrum, both H-3 (δ H 4.07) and H-5 (δ H 3.08 and 3.12) were correlated with δ C 55.7 (t), suggesting the methylene was connected with N 4 .…”

“…6 In the current study, separation of total alkaloids led to seventeen MIAs besides alstrostines A and B. 7 In this paper, we will describe the isolation and structural elucidation of other four new alkaloids alstrostines C-F (1-4) together with thirteen known isolates, 19,20-dihydroakuammicine (5), echitamidine (6), 12-methoxyechitamidine (7), 19-oxo-12-methoxyechitamidine, vallesiachotamine (9), isovallesiachotamine (10), deacetylakuammiline (11), 17-O-acetyl-N 4 -demethylechitamine (12), N 4 -demethylechitamine (13), akuammidine (14), 6,7-secoangustilobine (15), undulifoline (16), tabersonine (17). The biogenetic pathway of the new alkaloids was proposed.…”

Why are the terpenoid indole alkaloids of type I homochiral?

“…Case 1: secologanin (1a) and tryptamine (2a), in the presence of strictosidine synthase, gave strictosidine (3S-6a) with complete stereoselectivity. 11,12 Case 2: the reaction of secologanin (1a) and tryptamine (2a), in the absence of strictosidine synthase, provided strictosidine (3S-6a) and vincoside (3R-6a) without stereoselectivity; however, this latter compound could be isolated only in the form of vincosamide (3R-10). 13 Case 3: tetreaacetyl secologanin (1b) and pbromobenzyl tryptamine (2b) afforded tetraacetyl-pbromobenzyl vincoside (3R-6b) with high stereoselectivity at C-3.…”