Table 1.

¹H- (400 MHz, CDCl₃) and ¹³C- (100 MHz, CDCl₃) NMR data, ¹H–¹H COSY and HMBC correlations for diterpenoid 1.

Position	δH (J in Hz)	δC, Mult.	1H–1H COSY	HMBC (H→C)
1a/b	0.75 dd (8.4, 2.8); 1.42 m	19.9, CH2	H2-2, H-10	C-9, -10
2a/b	1.19 m; 1.49 m	23.2, CH2	H2-1, H2-3	C-1, -3, -4
3	1.58 m	32.1, CH2	H2-2	C-4, -18
4		17.4, C
5		26.3, C
6a/b	1.02 m; 1.80 td (14.0, 2.8)	27.6, CH2	H2-7	C-5, -7, -8, -10, -18
7a/b	1.35 m; 1.92 tt (14.0, 4.0)	27.9, CH2	H2-6, H-8	C-6, -8, -19
8	1.68 m	35.6, CH	H2-7, H3-19	C-6, -7, -9, -19
9		39.1, C
10	1.64 dd (12.4, 4.0)	40.9, CH	H2-1	C-8, -9, -10, -20
11	1.39 m; 1.59 m	35.5, CH2	H2-12	C-8, -9, -12
12	2.35 dd (8.8, 7.2)	21.5, CH2	H2-11, H-14	C-11, -13, -14, -16
13		171.2, C
14	5.84 br s	116.9, CH	H2-12	C-12, -13,-15
15		171.8, C
16	6.01 s	99.2, CH		C-13, -15
17	1.04 s	22.4, CH3		C-3, -4, -5
18a/b	0.13 d (4.4); 0.52 d (4.4)	24.5, CH2		C-3, -4, -5, -6, -10, -17
19	0.97 d (7.2)	14.2, CH3	H-8	C-7, -8, -9
20	1.00 s	19.8, CH3		C-8, -9