Journal of Natural Products Figure 1. Key COSY and HMBC correlations in the aglycone moiety of pseudonocardone A (1). Figure 2. Key COSY and HMBC correlations in the sugar moiety of pseudonocardone A (1). (121.6), indicating that C-12 is reduced in 1 to give a hydroquinone tautomer rather than a quinone as found in 5. Additional signals were present in the NMR spectra of 1 that could not be attributed to the angucycline core. Subtracting the atoms accounted for by the hydroquinone substructure showed that the remaining fragment had to account for C6H9O6. A series of oxygenated methine resonances in the HSQC spectrum (δC 73.1−77.1 and δH 3.63−4.16) and a resonance typical of an anomeric carbon (δC 103.8 and δH 5.23) suggested that 1 was glycosylated. An HMBC correlation from the anomeric proton at δH 5.23 to δC 156.9 (C-1) showed that 1 Note was glycosylated at the oxygen atom attached to C-1. A series of COSY and HMBC correlations (Figure 2) revealed that the sugar was a hexose. Finally, HMBC correlations from δH 3.76 (H-4′) and 4.16 (H-5′) to a carbonyl carbon at δC 173.0 (C-6′) showed that the sugar had been oxidized to the carboxylic acid at C-6′. The relative conﬁguration of the sugar residue in 1 was determined by coupling constants and a NOESY experiment. Large coupling constants (J values ranged from 7.6 to 10.0 Hz; see Table 1) indicated that all of the protons must be axial, and therefore the sugar corresponds to β-glucuronic acid. This assignment was supported by NOESY correlations between δH 5.23 (H-1′) and δH 3.63 (H-3′), between δH 5.23 (H-1′) and δH 4.16 (H-5′), between δH 3.93 (H-2′) and δH 3.76 (H-4′), and between δH 3.63 (H-3′) and δH 4.16 (H-5′) (Figure 3). The absolute conﬁguration of the sugar moiety was not determined. The absolute conﬁguration of C-12 was also not determined. Figure 3. NOESY correlations in the sugar moiety of pseudono- cardone A (1). Pseudonocardone B (2) gave a peak in the HRESI(+) MS consistent with a molecular formula of C26H22O10. The molecular formula of 2 diﬀered from that of 1 by the loss of Table 1. 1H and 13C NMR Data for Pseudonocardones A (1), B (2), and C (3) Recorded in CD3OD at 600 MHz pseudonocardone A (1) pseudonocardone B (2) pseudonocardone C (3) position 1 2 3 4 4a 5 6 6a 7 7a 8 9 10 11 11a 12 12a 12b 13 14 1′ 2′ 3′ 4′ 5′ 6′ δC 156.9 114.7 140.5 124.0 139.4 130.0 124.5 132.5 186.0 120.8 161.1 112.8 136.0 123.8 147.7 66.5 139.6 121.6 21.8 49.4 103.8 75.0 77.1 73.1 76.7 173.0 δH (J in Hz) 7.21, s 7.37, s 7.78, d (8.8) 8.10, d (8.2) 7.13, d (8.2) 7.64, t (7.9) 7.34, d (8.6) 6.93, s 2.47, s 3.95, s 5.23, d (7.6) 3.93, t (8.8) 3.63, t (9.4) 3.76, t (9.4) 4.16, d (10.0) δC 154.7 115.8 141.8 122.9 135.4 134.4 123.0 135.0 182.8 120.8 160.3 118.3 136.7 119.3 139.9 189.5 138.8 119.5 21.6 56.4 101.8 74.5 77.1 72.6 76.1 172.6 δH (J in Hz) 7.25, s 7.45, s 8.06, d (8.2) 8.16, d (8.8) 7.47, d (8.8) 7.78, t (7.9) 7.62, d (7.6) 2.52, s 4.01, s 5.26, d (7.0) 3.58, m 3.59, m 3.60, m 3.98, d (9.4) δC 144.7 134.7 120.3 131.9 133.0 122.8 137.1 183.1 119.9 160.5 119.3 136.5 121.1 138.4 190.8 133.2 121.0 17.0 56.6 106.6 75.1 77.2 72.9 76.8 173.5 δH (J in Hz) 6.95, s 8.97, d (9.4) 8.17, d (8.8) 7.49, d (8.2) 7.75, t (7.9) 7.78, d (7.0) 2.50, s 3.99, s 4.76, d (7.6) 3.71, dd (9.1, 7.9) 3.50, t (9.1) 3.63, t (9.4) 3.55, d (10.0) 1807 dx.doi.org/10.1021/np300380t | J. Nat. Prod. 2012, 75, 1806−1809