Maculosin, a non-toxic antioxidant compound isolated from Streptomyces sp. KTM18

Figures & data

Figure 1. DPPH free radical scavenging activity of seven days old culture broth extract (50 µg) of KTM12–KTM24.

Figure 2. Molecular structure of maculosin.

Table 1. NMR data for compound 1 (400 MHz, DMSO-d₆).

Position	δC	C-type	δH (mult. J Hz)	HMBC (1H-C)	COSY
1	– (N)	–	–	–	–
2	166.9 (C-2)	C═O	–	–	–
3	57.9 (C-3)	CH	4.36(t, 4.6, H–3)	3, 2.10, 11	–
4	– (N)	–	–	–	–
5	170.7 (C-5)	C═O	–	–	–
6	60.1 (C-6)	CH	4.04 (ddd, 10.8, 6.3, 1.4, H-6)	5, 6, 7, 8	–
7	29.4 (C-7)	CH2	2.07–2.12 (1H, m, H-7) 1.19–1.26(1H, m, H-7′)	5, 6, 7, 8	1.81, 4.04
8	22.7 (C-8)	CH2	1.78–1.83 (2H, m, H-8)	7, 8, 9	1.23, 3.53
9	45.9 (C-9)	CH2	3.51–3.57 (1H, m, H-9), 3.34–3.38 (1H, m, H-9′)	2, 6, 7, 8, 9	1.81
10	37.7 (C-10)	CH2	3.09 (1H, dd, 14.2, 4.6, H-10), 3.03 (1H, dd, 14.2, 4.6, H-10′)	3, 2, 10, 11, 12, 16	4.36
11	127.9 (C-11)	Cq	–	–	–
12	132.4 (C-12)	CH	7.01(d, 8.4, H-12)	3, 10, 12, 13, 14, 15, 16	6.72
13	116.2 (C-13)	CH	6.72(d, 8.4, H-13)	11, 13, 14, 15	7.01
14	157.7 (C-14)	C-OH	–	–	–
15	116.2 (C-15)	CH	6.72(d, 8.4, H-15)	11, 13, 14, 15	7.01
16	132.4 (C-16)	CH	7.01(d, 8.4, H-16)	3, 10, 12, 13, 14, 15, 16	6.72

Table 2. Antioxidant activity and brine shrimp toxicity activity of maculosin.

Test samples	DPPH free radical scavenging activity (50% inhibition, IC50) (µg/mL)	Brine shrimp lethality test (50% lethal dose, LD50) (µg/mL)	Remark
Maculosin	2.16 ± 0.05	NA^a
BHA	4.8 ± 0.15	–	+ve control
Berberine chloride	–	8.63 ± 0.55	+ve control

NA: no activity.

^a Activity was not observed until the test concentration of 128 µg/mL.