High Resolution ¹H-NMR and ^C-NMR Spectra of Saturated Pyrrolizidine Monoester Alkaloids

Abstract

spectra of saturated pyrrolizidine monoester alkaloids and the aminoalcohols tracheianthamidine (4), isoretronecanol (10), supinidine (11) and curassanecine (12) have been determined at 270 MHz in CDClj and CeD6. Also chemical shifts and coupling constants are tabulated. Evidence is presented that viridiflorates and trachelanthates can be differentiated by means of a) chemical shifts of the magnetically non-equivalent isopropyl methyl groups in CeDe and b) chemical shifts and patterns of the H-4' and H-9 signals. 15C-nmr spectra of these substances measured at 67.89 MHz are also reported. Chemical shift trends are presented and another method for distinguishing viridifloric and trachelanthic esters on the basis of the chemical shifts of the methyl carbons is discussed.

Pyrrolizidine Alkaloids from Heliotropium megalanthum

“…The 1 H NMR spectrum of 1 showed signals at δ H 0.83 (d, J = 6.8 Hz, H-7‘), 0.93 (d, J = 6.8 Hz, H-6‘), 2.08 (m, H-5‘), 3.98 (q, J = 6.8 Hz, H-3‘), and 1.33 (d, J = 6.7 Hz, H-4‘), attributed to two isopropyl methyl groups, two methine signals, and one methyl signal, respectively, corresponding to the necic acid part of the alkaloid. These protons were correlated with the carbon signals at δ C 17.8 (q, C-7‘), 15.6 (q, C-6‘), 32.0 (d, C-5‘), 72.1 (d, C-3‘), and 17.0 (q, C-4‘) in the HMQC experiment (Table ), and are in agreement with 1 having a (2‘ R , 3‘ R )-(−)-viridiflorate ester unit (ΔδH 2 -9 = 0.37 and ΔδC-6‘/C-7‘ = 2.2). − Additionally, three methine protons were observed at δ H 4.29 (br t, J = 3.6 Hz), 3.48 (dd, J = 7.8, 4.0), and 2.78 (m). The downfield signal could be attributed to a proton geminal to the hydroxyl group.…”

Pyrrolizidine alkaloids from Ageratum houstonianum Mill

“…The assignment was performed by interpretation of H,H-and C,H-correlated spectra. Important structural information is provided by the 13 C chemical shift of C-6 (2: 35.7; 3: 33.7; 4: 34.2 ppm), C-7 (2: 70.1; 3: 73.7; 4: 74 ppm) and C-8 (2: 77.6; 3: 79.5; 4: 74.8 ppm) (Jones et al, 1982;Mohanraj and Herz, 1982;Wiedenfeld and Ro¨der, 1991). These signals determine a retronecine-O-9 ester 2, a heliotridine-O-9 ester 3 and a retronecine-O-7 ester 4.…”

“…The esterifying acid is characterized by the values for C-12 (76 ppm, S), C-13 (1.80 and 35 ppm) and the methyl groups 14/15 ($ 0.8 and $ 17 ppm) as well as for the methyl group 16 ( $ 1.2 and $ 23 ppm). The stereochemistry at C-12 can be deduced by interpretation of the shift-difference of the C-9H 2 AB system (Mohanraj and Herz, 1982;Wiedenfeld and Ro¨der, 1991). For this aspect a value near 0 is found indicating the S-configuration.…”

Pvrrolizidine Alkaloid Containina Plants Used in Mongolian Traditional Medicine: Lappula Myosotis Moench.

“…These signals determine a retronecine-0-9 ester for 1 and 2 and a retronecine-0-9-0-7 diester for 3 and 4, respectively [ I 9-21]. The stereochemistry at C-12 can be deduced by interpretation of the shift-difference of the C-9H2 ABsystem [20,21]. Values from 0-0.2 pprn indicate S-configuration, higher values the opposite one (AHz = 0.1 pprn in 1 -4).…”