Table 2.

¹H and ¹³C NMR spectral data of compounds 17, 18 and 21 (¹H for 700 MHz, ¹³C for 175 MHz).

	17a		18b		21a
No.	δH	δC, type	δH	δC, type	δH	δC, type
1		169.6, C		164.7, C		166.3, C
2
3	6.29, s	103.1, CH	6.75, s	100.7, CH		158.8, C
3a		148.9, C		151.7, C
4		119.0, C		112.4, C	6.87, d (1.4)	98.8, CH
5		174.3, C		166.3, C		167.8, C
6		121.4, C		120.9, C		105.6, C
7		160.7, C		163.1, C	6.67, s	120.3, CH
7a		111.4, C		109.6, C
8	3.54, s	56.1, CH3	3.60, s	56.9, CH3		144.5, C
9	4.60, s	65.3, CH2	4.44, s	61.3, CH2		168.0, C
10	3.38, s	58.1, CH3	3.27, s	57.7, CH3	3.76, s	52.0, CH3
11	4.65, s	67.2, CH2	10.14, s	192.5, CH	2.44, d (1.4)	13.6, CH3
12	3.38, s	58.4, CH3			1.92, s	8.8, CH3
13	3.99, s	63.0, CH3	4.14, s	63.4, CH3	4.02, s	57.5, CH3

^aIn CD₃OD.

^bIn DMSO-d₆.