Isolation, Synthesis, and Radical-Scavenging Activity of Rhodomelin A, a Ureidobromophenol from the Marine Red Alga Rhodomela confervoides

Abstract

A novel ureidobromophenol, rhodomelin A (1), was characterized from Rhodomela confervoides. Its structure was elucidated by spectroscopic analysis. Both enantiomers of 1 were synthesized using a convergent strategy starting from d/l-pyroglutamic acids, respectively, allowing assignment of the R-configuration for the naturally occurring isomer by chiral HPLC analysis. Rhodomelin A represents the first example of a naturally occurring ureidopyrrolidone alkaloid incorporating a γ-aminobutyric acid unit. The scavenging activity of 1 toward DPPH (1,1-diphenyl-2-picrylhydrazyl) and ABTS (2,2'-azinobis(3-ethylbenzothiazoline-6-sulfonate)) radicals was assayed.

Progress of Bromophenols in Marine Algae from 2011 to 2020: Structure, Bioactivities, and Applications

“…Similarly, the synthetic (S)-rhodomelin A ( 3.21 , Scheme 3 ) showed powerful inhibition of DPPH radicals with an IC 50 value of 8.9 μM. Although (S)-rhodomelin A was not so strong as (R)-rhodomelin A ( 3.20 ), it was more potent than the positive control BHT (IC 50 = 82.13 μM) [ 44 ].…”

“…In the last decade, novel BPs and more of their bioactivities have been reported. Moreover, it is worth noting that more studies have focused on the design and synthesis of novel functional derivatives of BPs [ 39 , 40 , 41 , 42 , 43 , 44 , 45 , 46 ], as well as on the illustration of the mechanisms underlying their bioactivity, than only focusing on the isolation and testing the biological activity of BPs found in natural products. Therefore, it is necessary to report these new findings, and so in the present review, we mainly focus on the biological activities of newly discovered BPs from marine algae and also on some of BPs’ representative derivatives synthesized in the last ten years.…”

Metabolites with Antioxidant Activity from Marine Macroalgae

“…A series of BPs ( 3 , 4 , 6 , 9 – 11 , 13 – 16 , 18 , 19 , 21 , 22 , 24 , 27 – 32 , 34 – 39 , 42 , 45 , 47 , 50–52 , 56 , 65 ) have been isolated from the red alga R. confervoides [ 76 , 77 , 81 , 83 , 85 ]. Among them, compounds 10 , 15 , 16 , 18 , 19 , 37 , 38 , 39 , 42 , and 65 exerted the highest antioxidant activity with IC 50 values of 7.43, 5.43, 5.70, 3.82, 9.52, 8.72, 9.40, 7.62, 5.22, and 8.90 µM, respectively, with all but 37 and 38 bearing a 2,3-dibromo-4,5-dihydroxy-benzyl skeleton.…”

Cadinane and carotane derivatives from the marine algicolous fungus Trichoderma virens RR-dl-6-8

“…6 eluted with CH 2 Cl 2 /MeOH (20:1) and was further purified by CC on RP-18 (MeOH/H 2 O, 1:1) and Sephadex LH-20 (MeOH) and preparative TLC (CH 2 Cl 2 /MeOH, 15:1) to afford 3 (49.4 mg), 5 (10.8 mg), 6 (52.6 mg), and 7 (6.4 mg). 13 C NMR data, Tables 1 and 2; EIMS m/z (%) 362 [M] + [3], 344 [3], 327 [4], 312 [24] 13 C NMR data, Tables 1 and 2; EIMS m/z (%) 268 [M] + [24], 250 [7], 236 [25] 1 and 2; EIMS m/z (%) 268 [M] + [24], 250 [7], 236 [19] 1 and 2; EIMS m/z (%) 280 [M] + [26], 262 (39), 249 [18], 238 [26], 221 [27], 207 (100), 203 (45), 195 [23], 177 [17], 43 [20] 13 C NMR data, Tables 3 and 4; EIMS m/z (%) 274 [M] + [12], 259 [11], 243 [28], 216 (100), 184 [24], 157 (68), 128 [27] 13 C NMR data, Tables 3 and 4; EIMS m/z (%) 234 [M] + (89), 219 [10],…”

“…Several halogenated polyketides and peptides have been discovered from Trichoderma species [14][15][16][17], but halogenated terpenes have only been found in a T. virens strain (FY06) [5]. In order to further obtain the halogenated metabolites from this species, an algicolous strain (RR-dl-6-8) obtained from the organohalogen-enriched marine red alga Rhodomela confervoides was chemically examined [18]. Our efforts led to the discovery of eight cadinane derivatives, trichocadinins H − N (1-7) and methylhydroheptelidate (8), and two carotane sesquiterpenes, 14-O-methyltrichocarotin G (9) and 14-O-methyl CAF-603 (10) (Fig.…”