Cycloeucalen-3ß-(2-methyl Butanoate). New Cycloeucalen Isolated from the Espeletia barclayana Cuatr (Asteraceae)

Continuing our studies of the Espeletia barclayana Cuatr. [1,2] we describe the isolation and characterization of another new cycloeucalen triterpene, cycloeucalen-3ß-(2'-methyl butanoate). It's structure was established using spectroscopic methods ¹H and ¹³C NMR: 600 MHz, and 150 MHz (1D:¹H, ¹³C-JMOD; 2D:COSY, NOESY, HMBC).

The sample of E. barclayana Cuatr. was collected at páramo del Tablazo, Subachoque, Cundinamarca, Colombia, and identified by Mr. Santiago Diaz of the Herbario Nacional Colombiano (Col. 332528). The dried and ground leaves (1kg) of E. barclayana were extracted with petrol and 20g of this extract was subjected to column chromatography over Si-gel using petrol and EtOAc as eluents. The petrol fraction gave a mixture of two compounds that were separated using TLC preparative development repeatedly with n-hexane:benzene (1:1). Cycloartan-3ß-(2-methyl butanoate) [1] and a new cycloeucalen derivative were obtained and purified by several times of recrystallization with CHCl3 and MeOH.

¹H NMR spectra of the cycloeucalene showed doublet signals at d 0.15 and 0.40 with J=3.7 Hz for CH2 of cyclopropane ring and d 4.66 4.67 for =CH2. The chemical shifts of the cyclopropyl methylene protons (d 0.15 and 0.40) are consistent with the presence of only one methyl group at C-4 [ 3,4]. The presence of the methylene group was confirmed by the ¹³C NMR signal at d 105.9 and its position on C-24 was determined using ¹H-¹H COSY and ¹H-¹H NOESY spectra (see data in Table 1). The ¹H NMR spectrum clearly indicated the b-equatorial nature of the C-3 ester group (4.5, heptuplet, Jax-eq =5 Hz , Jax-ax = 11Hz, 3aH).

Mp 132-134 ^oC

[a]20D = +47 º (0.0068 g/mL, CHCl3).

¹H NMR (600 MHz, CDCl3): 0.85 (d, H3-21), 0.91 (9H, H3-21, H3-29, H3-4' ), 0.97 (s, H3-18), 1.02 and

1.03 (H3-26 and H3-27), 1.14 (d, H3-H-2''), 0.15 (d, J=3.7 Hz, H-19a) and 0.40 (d, J=3.7Hz, H-19ß), 2.24

(heptuplet, J=7Hz, H-25), 2.35 (hexuplet, J= 7Hz, H-2'), 4.5 (m, heptuplet, Jax-eq=5, Jax-ax=11, CH-O H-3), 4.66-4.67 (d, =CH2) .

¹³C NMR (150 MHz, CDCl3): 30.9(C-1), 27.2 (C-2), 78.2 (C-3), 41.3 (C-4), 43.0 (C-5), 25.1 (C-6), 24.7

(C-7), 46.9 (C-8), 23.6 (C-9), 29.3 (C-10), 30.5 (C-11), 32.8 (C-12), 48.9 (C-13), 45.8 (C-14), 35.3

(C-15), 28.1 (C-16), 52.2 (C-17), 17.8 (C-18), 26.9 (C-19), 36.12 (C-20), 18.3 (C-21), 34.9 (C-22), 31.3

(C-23), 156.9 (C-24), 33.7 (C-25), 21.8 (C-26), 22 (C-27), 14.3 (C-28), 19.1 (C-29), 18.3 (C-30), 105.9

(C-24') 176.0 (C-1'), 41.6 (C-2'), 26.7 (C-3'), 11.7 (C-4'), 16.7 (C-2" ).

Table 1. Spectral data and assigments for proton and carbon on ¹H NMR and ¹³C NMR:

Table 1. Spectral data and assigments for proton and carbon on ¹H NMR and ¹³C NMR:

Some correlation observed on HMBC and NOESY spectra: