Table 2.

¹H and ¹³C NMR data ^a of diterpenes 1–4.

Position	Chemical Shift in ppm
	1H (coupling constant J in Hz)			13C
	1 b	2 b	3 + 4 c	1 b	2 b	3 + 4 c
1	6.47 br d (1.2), 1H	6.47 d (1.0), 1H	6.91 d (1.2), 1H	127.8	129.1	129.0
2	-	-	-	185.8	185.7	187.2
3	6.78 d (1.3), 1H	6.78 d (1.0), 1H	6.80 d (1.2), 1H	131.4	130.9	131.7
4	-	-	-	150.7	151.3	152.4
5	-	-	-	53.5	55.1	54.3
6	1.45 ddd (3.7, 13.3, 17.5), 1H	1.44 ddd (9.3, 13.5, 17.7), 1H	1.51 ddd (4.0, 13.5, 17.5), 1H	33.1	33.2	33.9
	3.11 dt (3.0, 6.1), 1H	3.12 dt (3.3, 13.3), 1H	3.00 m, 1H
7	1.71 m, 1H	1.65 m, 1H	1.66 m, 1H	26.5	27.2	27.5
	2.78 m, 1H	2.49 ddd (4.2, 13.9, 17.1), 1H	2.66 m, 1H
8	1.75 m, 1H	1.78 m, 1H	1.82 m, 1H	39.7	43.7	40.0
9	-	-	-	55.0	53.6	55.9
10	-	-	-	155.4	155.7	156.2
11	2.78 m, 1H	2.69 dd (8.2, 14.3), 1H	2.80 m, 1H	38.9	39.2	36.9
	2.65 dd (11.1, 14.5), 1H	2.94 dd (6.3, 14.2), 1H	2.93 m, 1H
12	5.55 dd (5.2, 11.1), 1H	5.57 t (7.0), 1H	5.72 dd (5.5, 11.1), 1H	71.3	72.0	72.4
13	-	-	-	123.5	125.0	135.0
14	6.45 m, 1H	6.41 m, 1H	7.40 and 7.39 br s, 1H	108.1	107.8	149.8
15	7.47 br t (1.5, 3.1), 1H	7.49 br d (1.6), 1H	6.20 and 6.18 br s, 1H	144.4	144.6	99.3
16	7.54 br s, 1H	7.45 m, 1H	-	140.5	139.7	170.9
17	1.17 d (6.4), 3H	1.23 d (6.7), 3H	1.15 d (5.8), 3H	16.9	17.7	17.1
18	-	-	-	165.3	165.5	166.7
18-OMe	3.84 s, 3H	3.84 s, 3H	3.71 s, 3H	53.0	52.9	53.3
19	-	-	-	166.3	166.7	168.4
19-OMe	3.65 s, 3H	3.71 s, 3H	3.60 s, 3H	53.2	53.1	53.7
20	-	-	-	172.2	173.1	174.0

^a All assignments were confirmed unequivocally as based on COSY, HSQC, HMBC and NOESY experiments; Spectra obtained in: ^b CDCl₃ (300 MHz for ¹H and 75 MHz for ¹³C NMR, respectively) and ^c CD₃OD (600 MHz for ¹H and 150 MHz for ¹³C NMR, respectively).