Oxidative biotransformation of stemofoline alkaloids

Figures & data

Figure 1. TLC Chromatograms of the starting materials (1a, 2a and 3a) and transformation products (1b, 2b, 3b and 3c) were sprayed with ammonium molybdate reagent and the mobile phase are 96:4, 93:7 and 90:10 v/v of CH₂Cl₂ and MeOH.

Figure 2. TLC Chromatograms of the starting materials (1a, 2a and 3a) and transformation products (1b, 2b, 3b and 3c) were sprayed with Dragendroff’s reagent and the mobile phase are 96:4, 93:7 and 90:10 v/v of CH₂Cl₂ and MeOH.

Figure 3. (a) The microbial transformations of 1a, 2a, 3a and 4 using Cunninghamella elegans and (b) 5 (the C-6 epimer of 1b).

Table 1. ¹H and ¹³C NMR spectroscopic data of compounds 1b–3b in CDCl₃.

position	1b		2b		3b
	δC^atype	δH^b (J in Hz)	δC^atype	δH^b (J in Hz)	δC^atype	δH^b (J in Hz)
1	32.9, CH2	1.76 m 1.94 d (12.2)	33.4, CH2	2.03 m 1.85 m	32.6, CH2	1.92 d (12.2) 1.79 d (12.3)
2	78.9, CH	4.23 br,s	79.1, CH	4.35 br,s	81.2, CH	4.20 s
3	83.1, C	–	82.9, C	–	82.8, C	–
5	58.7, CH2	3.47 m 3.09 m	58.4, CH2	3.22 dd (14.6,3.4)	60.0, CH2	3.50 m
6	73.0, CH	4.29 m	72.7, CH	4.31 m	73.7, CH	4.22 m
7	58.4, CH	2.77 m	59.8, CH	2.71m	59.9, CH	2.94 m
8	110.3, C	–	109.8, C	–	110.4, C	–
9	49.2, CH	1.52 m	49.0, CH	1.52 m	49.2, CH	1.47 m
9a	60.0, CH	3.47 s	60.2, CH	3.50 br,s	60.5, CH	3.50 s
10	34.7, CH	3.06 m	34.6, CH	3.06 m	34.7, CH	3.03 m
11	148.2, C	–	147.9, C	–	148.0, C	–
12	128.1, C	–	128.7, C	–	128.2, C	–
13	162.9, C	–	162.9, C	–	162.9,C	–
14	98.8, C	–	98.9, C	–	98.9,C	–
15	169.9,C	–	170.0, C	–	169.8,C	–
16	9.3, CH3	2.07 br,s	9.3, CH3	2.07 s	9.3, CH3	2.07 br,s
17	18.3, CH3	1.35 d (6.5)	18.2, CH3	1.35 d (6.6)	18.4, CH3	1.36 d (6.5)
OMe	59.0, CH3	4.14 br,s	59.0, CH3	4.14 s	59.0, CH3	4.14 br,s
1′	27.6, CH2	1.29 m 1.44 m	36.5, CH2	1.81 m	127.1, CH	5.66 d (15.5)
2′	32.0, CH2	1.82 t (7.8)	71.6, CH	3.61 m	134.3, CH	5.93 m
3′	23.2, CH2	0.91 m 1.37 m	30.6, CH2	1.43 m 1.29 m	25.5, CH2	2.10 m
4′	14.2, CH3	0.91 t (7.0)	9.9, CH3	0.94 t (7.5)	13.6, CH3	1.00 d (7.4)

^aData recorded at 100 MHz. ^bData recorded at 400 MHz.

Table 2. The IC₅₀ values (µM) for acetylcholinesterase inhibitory of activities of the starting materials (1a, 2a and 3a) and biotransformation products (1b, 2b, 3b and 3c).

Compounds	EelAChE IC50 (µM)
1a	45.1 ± 5.46^c
1b	11.0 ± 1.49^b
2a	90.4 ± 3.15^d
2b	40.4 ± 4.17^c
3a	44.6 ± 3.89^c
3b	178 ± 14.55^e
3c	41.6 ± 4.42^c
Galantamine	1.50 ± 0.16^a

^abceMeans with the same superscript are not significantly different. Values with the same letter are not significantly different (p = .05) according to Duncan’s multiple range test.

Figure 4. Molecular model of compound 1b generated in SPATAN 18 using DFT calculations (ωB97X-D/6-31G*) of the equilibrium geometry (gas phase).

Table 3. Selected ¹H and ¹³C NMR spectroscopic data of compounds 1a, 1b and 5 in CDCl₃.

position	Stemofoline (1a)		(6R)-hydroxystemofoline (1b)		(6S)-hydroxystemofoline (5)
	δC^a type	δH^b (J in Hz)	δC^a type	δH^b (J in Hz)	δC^a type	δH^b (J in Hz)
1a 1b	33.1, CH2	2.03 m 1.85 m	32.9, CH2	1.76 m 1.94 d (12.2)	33.8, CH2	1.71 ddd (11.7,3.0,3.2) 2.05 m
2	78.2, CH	4.31 br,s	78.9, CH	4.23 br,s	78.8, CH	4.17 s
3	84.1, C	–	83.1, C	–	84.0, C	–
5a 5b	47.4, CH2	3.28 m 3.06 m	58.7, CH2	3.47 m 3.09 m	54.7, CH2	2.94 dd (14.5,3.6) 3.50 dd (14.4,8.8)
6	26.0, CH2	1.39 m 1.25 m	73.0, CH	4.29 m	74.7, CH	4.80 ddd (8.8,5.9,3.6)
7	49.8, CH	2.78 d (6.1)	58.4, CH	2.77 s	53.7, CH	2.76 d (5.9)
8	112.3, C	–	110.3, C	–	112.0, C	–
9	47.4, CH	1.88 m	49.2, CH	1.52 m	47.9, CH	2.80 dd (12.1,3.6)
9a	61.6, CH	3.68 s	60.0, CH	3.47 m	60.8, CH	3.55 m
10	34.5, CH	3.14 m	34.7, CH	3.06 m	34.9, CH	3.10 dq (10.0, 6.6)
17	18.7, CH3	1.38 d (6.6)	18.3, CH3	1.35 d (6.5)	18.2, CH3	1.38 d (6.6)

^aData recorded at 100 MHz. ^bData recorded at 400 MHz..

Data availability statement

The supporting data in this research is included within the article, and the data are available from the corresponding author upon request.