Terpenes dominated the ranking of new structures elucidated with 192 new compounds reported in 188 studies between 2021 and 2022, in 184 different botanical species. In second place are alkaloids, with approximately 70 new molecular skeletons described in 69 different botanical species. The Flavonoids class had 55 new molecules elucidated, in a variety of 53 botanical species. New phenolic structures were elucidated from 54 different botanical species, with 52 new molecules reported between 2021 and 2022.
We also included the class of coumarins and anthraquinones in our compounds class section, which even with a relatively smaller number of new compounds elucidated, are among the most important studies on new natural structures.
5.1. Terpenes
Terpenes are composed of simple hydrocarbons formed by isoprenic units from the mevalonate pathway. The classification is established by the number of isoprenic units present in the molecule, being hemiterpenes characterized by the presence of only one isoprenic unit (C5), monoterpenes by two units (C10), sesquiterpenes (C15), diterpenes (C20), triterpenes (C30) and tetraterpenes (C40).
Three new polyprenylated acylphloroglucinol meroterpenoids were obtained from the aerial parts of
Hypericum forrestii (Chitt.) N. Robson (Hypericaceae), called hyperiforins A-C [
26]. Hyperiforins A (
2) and C (
3) showed potent inhibitory action on the enzyme tyrosine phosphatase 1B.
Three new glycosidic monoterpene compounds (
4) (with glucopyranosyl and apiofuranosyl groups) derived from Carvacrol were obtained from the roots of
Lilium dauricum Ker Gawl. (Liliaceae). It is interesting to note that, despite the small structural difference (exchange of the position of the sugars and methyl), different potency in the α-glucosidase inhibitory action was found [
48].
Iridoids are undoubtedly the class of monoterpenes with the greatest potential for providing new structures [
49,
50,
51,
52]. Cornusdiridoids (
4) with unusual cornuside-morroniside secoiridoid dimers were obtained from the fruits of
Cornus officinalis. Their small differences consisted in stereochemical and sugar position. The were tested for antidiabetic activity, but just the already known compounds were active [
53]. Chlorine-containing iridoid glycosides were reported from
Plantago maxima Juss. ex Jacq (Plantaginaceae) (
5) [
54],
Valeriana jatamansi Jones (
6) (Caprifoliaceae) [
55], as well as secoiridoids [
50,
52,
56].
Considering sesquiterpenes, there was a wide variety of subclasses making up the new structures identified. Among the guaiane-type skeletons, a dimeric (
11) was found from the leaves
Xylopia vielana Pierre (Annonaceae) together with different analogues [
57]. Compound
12 was obtained from the leaves of
Ammoides atlantica (Coss &Durieu) H. Wolff (Apiaceae), together with 15 new compounds [
58]. The guaianolide lactone
13 was obtained from
Chrysanthemum indicum L. (Asteraceae), a traditional herbal medicine in South Korea [
59]. It showed inhibitory effects on lipopolysaccharide (LPS)-induced nitric oxide production in RAW 264.7 cells. The guaianolide
14 was obtained from the plant
Ambrosia artemisiifolia L. (Asteraceae), an invasive plant with known allelopathic effects [
60].
An unusual guaianolide trimer (
15) was found in
Ainsliaea fragrans Champ. (Compositae), a plant with medicinal use as an antibacterial and anti-inflammatory [
61]. The third sesquiterpene unit is attached to C
2′, providing a rare linkage (C
2′-C
15″). Cytotoxicity results showed this compound active against five cancer cell lines with IC
50 values of 0.4−8.3 μM. Compound
16 is notable for the presence of a γ-lactam group [
35], while
17 has an unusual 1,4-peroxy hemiacetal xanthanolide skeleton [
62]. Other minor structural modifications can be found in the reported sesquiterpenes
18 and
19 [
63].
Eudesmane-type sesquiterpenoids are another important subclass of sesquiterpenoids with several examples of new structures (
20-
26) [
37,
58,
64,
65,
66,
67,
68]. Compounds
25 and
26 have rare peroxide-substituted group and γ-lactam ring. The first was isolated from
Sonchus arvensis L. (Asteraceae) and showed phytotoxic activity. Compound
26 was obtained from
Sarcandra glabra (Thunb.) Nakai (Chloranthaceae) together with five other new eudesmane-type sesquiterpenoids.
Tian and co-workers isolated 5,5-spiroketal sesquiterpenes (
27) from the roots of
Angelica pubescens, which possessed inhibitory activity against nitric oxide (NO) production induced by lipopolysaccharide (LPS) in RAW264.7 macrophage cells [
69]. Dihydro-β-agarofuran-type sesquiterpenoids were identified from the stems of
Celastrus monospermus Roxb. (Celastraceae) with significant inhibition of osteoclastogenesis [
70]. Celasmondin C (
28) possessed an unusual nicotinoyloxy group attached to C-1.
Germacrenolide-type was found in
Carpesium lipskyi Winkl. (Asteraceae) [
71],
Polydora serratuloides (DC.) H. Rob (Asteraceae) [
72],
Asteriscus graveolens (Forsk) Less. (Asteraceae) [
73] and
Carpesium divaricatum Sieb.et Zucc (Compositae) [
74].
Seterterpenoids are relatively rare in nature. Mirzania and co-workers isolated six new (
29) from
Salvia mirzayanii Rech. f. and Esfand [
75].
Regarding diterpenes, a new ent-kaurane diterpenoid compound named daturoside A (
30) was obtained from the pericarp of
Datura metel L. from the Solanaceae family [
76]. The author’s studies indicate an anti-inflammatory action through the production of nitric oxide (NO) induced by lipopolysaccharide (LPS). The compound hupehenoside A (
31) was obtained from
Inula hupehensis (Y. Ling) Y. Ling and has a carbon bond in the glycosidic structure and a carboxylic acid in the cyclic structure [
77]. Wang et al (2022) also identified another 15 new compounds with a similar structure, with slight variations in the hydroxyls of the sugars (mostly acetylation substitutions). The authors evaluated the neuro-anti-inflammatory activity, and only one of the compounds showed inhibition of NO production.
Other diterpenes with ent-kaurane skeletons were reported by Wei et al., 2022 [
78] and Xin et al., 2022 [
79]. The molecule
32 has more hydroxyls in its structure than the already known molecule Phyllanthone A. It was isolated from the ethanolic extract of the aerial parts of
Rabdosia rubescens (Hemsl.) Hara (Lamiaceae). The study by Xin et al (2022) also reported two other ent-kaurane diterpenes from the roots and stems of
Phyllanthus acidus (L.) Skeels (Phyllanthaceae) with cytotoxic activity against some cancer cell lines and moderate anti-inflammatory action (
33).
Studying the plant
Euphorbia dracunculoides Lam. belonging to the Euphorbiaceae family, Yan et al. (2022) [
80] reported four new polycyclic diterpenoids. According to the author, compound
34 is the first example of a 15,16,17-trinorabietane aromatic diterpenoid, while compound
35 is an unusual 17-norabietane diterpenoid. They showed significant antiproliferative activity in four cancer cell lines, above all by inhibiting the proliferation of K562 cells.
Abietane diterpenoids are characterized by having a tricyclic chain and 20 carbons. Six new compounds were reported by Liu et al., (2022) [
81], which were obtained from the heartwood of
Juniperus formosana Hayata (Cupressaceae). Among the compounds obtained, four cadnene sesquiterpenoids Junipertriol (
34), an abietane diterpenoid (
35) and a β-naphthol1-(6-hydroxy-4-methylnaphthalen-2-yl) ethan-1-one derivative (
36). The compound Junipertriol (
34) showed significant NO inhibitory potential and all the new compounds showed anti-inflammatory effects, evaluating the expression of IL-1β, IL-6 and TNF-α was measured through LPS stimulation in RAW264.7 cells (Figure 19).
Another abietane diterpene compound was reported and named mutabilol, the compound was obtained from the leaves of Plectranthus mutabilis Codd (Lamiaceae) [
82]. The chemical structure of mutabilol (
37) shows two carbonyls in its non-aromatic cyclic structure.
Pimarane (
38 and
39) and abietane (
40) diterpenoids were obtained from the aerial parts of
Blumea balsamifera (L.) DC (Asteraceae) [
83]. The compounds showed anti-inflammatory action by inhibiting LPS induced by TNF-α. Among the pimarane-type structures, blusamiferoid E has a hydroxyl in the cyclic structure and an extra unsaturation, while blusamiferoid A has a carboxylic acid.
Li et al, (2022) reported three new 3,4-seco pimarane diterpene compounds from the leaves and twigs
of Isodon flavidus (Hand.-Mazz.) H. Hara (Lamiaceae) [
84]. The structure shows a δ-lactone ring and the carbon-carbon double bond of the isopropyl group seems to be related to antiviral activity. Among the compounds discovered, fladin C (
41) was the only one to show inhibition of Ebola virus replication.
A new 15,16-dinor-ent-pimarane diterpene was obtained from
Croton yunnanensis W.W. Sm. (Euphorbiaceae) and was named Crotonyunnan E (
42) [
85]. In addition to this compound, four other 19-cleodane diterpenes (Crotonyunnan A-D) were obtained [
85]. Crotonyunnan E (
42) showed selective cytotoxicity against three tumor cell lines SMMC-7721 (human hepatoma cells), HL-60 (pre-myelocytic leukemia) and A-549 (lung cancer cells).
Labdane diterpenes are characterized by a bicyclic structure, with decalin as the core. From the leaves of
Stevia rebaudiana (Bertoni) Bertoni, Kang et al, (2022) [
86] reported a new labdane diterpene compound (6-O-acetyl-(12R)-epiblumdane) (
43). Studies of this compound showed stimulation of insulin secretion in INS-1 β-pancreatic cells from rats.
An unusual indolic diterpene with a C-17 norcassane structure was obtained from the roots of
Euphorbia fischeriana Steud (Euphorbiaceae) [
87], in addition to another ent-atisane-type diterpene compound. The unusual compound was named Euphkanoid H (
44) and according to the author, it is the first example of an indolic diterpene with a C-17 norcassane structure in nature. In addition, the compound showed biological activity by inhibiting the proliferation of HEL cells, which could be effective in the development of drugs for leukemia.
A jatrophane diterpene was obtained from
Euphorbia glomerulans (Prokh.) Prokh. (Euphorbiaceae) and was named Euphoglophane V (
45); other jatrophane and ingenane type diterpenes have also been reported [
88]. According to the author, the compound has an isobutanoyloxyl group on the C-8 carbon and this new molecule showed high efficiency in reversing resistance to multiple drugs, promoting accumulation of Rh123 and DOX in drug-resistant cells, as well as inhibiting the transport function of P-glycoprotein, such action being interesting in therapies against cancer and fungal infection.
New C-19- diterpene alkaloids of the aconitine type were obtained from the aerial parts of
Aconitum apetalum (Huth) B. Fedtsch. (Ranunculaceae) and were given the names apetalrines A-E [
89]. The author’s research indicates that apetalrine B (
46) has neuroprotective action by inhibiting the production of reactive oxygen species (ROS) in SH-SY5Y cells, thereby inhibiting H2O2-induced cell apoptosis.
New limonoid (
47) was obtained from the leaves and twigs of
Walsura yunanensis C.Y.Wu (Meliaceae) and showed cytotoxic action on four cancer cell lines, including A549, HepG2, HCT116 p21KO and CNE-2 [
90]. The α,β-unsaturated ketone and portions of the A and B rings are essential for cytotoxic activity, according to the author.
A new saponin triterpenoid (
48) was isolated from the roots of
Gardenia ternifolia Schumach. & (Rubiaceae) and showed antimicrobial activity against
Salmonnella typhi [
91]. The compound named ternifoliaoside A (
48) has a saponin triterpene nucleus and two glucopyranosidic bonds.
Two new triterpenoid glycoside compounds were isolated from the fruits
of Momordica charantia L. (Cucurbitaceae) and were named Momordicoside Y and Z [
92]. Momordicoside Y (
49), along with other known compounds, were evaluated for their antidiabetic potential, showing inhibitory activity on hepatic gluconeogenesis.
Seven new triterpenes were obtained from the aerial parts of
Elsholtzia penduliflora W. W. Smith (Lamiaceae) [
93]. Two of the new compounds, named penduloside C (
50) and G (
51), showed significant inhibitory activity against tumor cells.
HU et al (2022) [
94] reported new triterpenoids obtained from the leaves of
Alstonia scholaris (L.) R. Br, and were named Alstolarnoid (A - D). These compounds - Alstolarnoid A (
52) and D (
53) - showed a reduction in uric acid levels in vitro and
in vivo.
Three new oleanane-type saponin triterpene compounds with a 13, 28 epoxy bridge were obtained from the roots of
Ardisia crispa (Thunb.) A. DC. and were named Ardisiacrispin D-F [
95]. These compounds showed cytotoxic action against three cancer cell lines (HeLa, HepG2 and U87 MG)
in vitro. According to the author, these new compounds are the first examples of a monosaccharide linked directly to the C3 aglycone of saponin triterpenes in this plant genus (Ardisiacrispin D -
54).
New triterpenic compounds were isolated from
Lepidozia reptans (L.) Dumort. and named lepidozin A-J [
96]. Lepidozin G (
55) is a 9,10-dry cycloartane that contains a cabonyl portion in an α,β-unsaturated portion in its structure that may be related to the inhibition of cancer cell lines by inducing the death of PC-3 cells by mitochondria-related apoptosis.
Among the terpenes, the sesqui- and diterpene subclasses have the greatest potential to present new structures, both due to the presence of atypical bonds between the carbons of the rings for the formation of extra rings, and the presence of some nitrogen derivatives. The possibility of skeleton types within sesqui- and diterpenes provides an even greater chance of finding new derivatives. In the other subclasses of terpenes, mostly minor modifications of functional groups and sugars are found.
5.2. Alkaloids
Piperidine alkaloids show various types of biological activity. Statistics considering the scaffolds of FDA-approved drugs show a widespread presence of the piperidine core [
97]. Wu et al. (2022) [
98] reports eight new 2,6-disubstituted piperidin-3-ol alkaloids (
56) possessing Angiogenesis-Inhibitory activity from the plant
Microcos paniculate L. (Tiliaceae). The variations in the structures were the number of -hydroxyls or carbonyls in the carbonic chain. Other piperidine alkaloids [
99] with small stereochemical variations and the presence of -CH
3 e -OH attached to the piperidinic ring has been reported from the plant
Alocasia macrorrhiza (L.) Schott (Araceae) (
57). These isolated alkaloids were screened for the antiproliferative activity through MTT assay against HepG2, AGS and MCF-7 tumor cells.
New amide alkaloids were isolated from the fruits of
Piper longum L. (Piperaceae) and given the names piperlongumamides D-F [
18]. The structure of piperlongumamide E (
58) is similar to the known compound retrofractamide A, differing by the stereochemistry of one of the double bonds. According to the author, piperlongumamide E (
58) showed inhibitory activity against NO production.
Diterpene alkaloids are found mainly in the genera
Aconitum,
Delphinium and
Spiraea in the Ranunculaceae family. Usually, they have a complex heterocycle scaffold (
3) and a variable number of carbons (C
18-, C
19-, C
20-). Three new C
20-diterpenoid alkaloids from
Aconitum kusnezoffii Reichb, named napellines were evaluated in vitro for their proliferative activities against A549, HL-60, MCF-7, Bel-7402, BGC-823, and RAW264.7 cells, but just the already known compounds showed activity. [
100] A similar new structure was found by Wang and co-workers (2021) [
101] in the plant
Aconitum carmichaelii Debx.
A rare C
20-type diterpene alkaloid was isolated from the plant
Delphinium gyalanum C. Marquand & Airy Shaw [
102]. This compound possesses a hemiacetal ring linking C-2 to C-19 and showed cardiotonic effect by isolated frog’s hearts perfusion (
4). Other activities were reported for diterpene alkaloids, as protective against cardiomyocytes H
2O
2-induced injurity [
103], anti-inflammatory effects against NO production [
104]. Kemgni et al. (2021) [
105] isolate sesquiterpenes alkaloids with an unusual eight-membered lactam ring (
4). They were obtained from the leaves of a Cameroonian medicinal plant
Greenwayodendron oliveri (Engl.) Verdc and showed antimicrobial activity.
Steroidal alkaloids have been reported from the plants
Veratrum grandiflorum (Maxim. ex Miq.) O.Loes. (Melianthiaceae) [
106,
107] with anti-inflamatory and cytotoxic activities. Two new pregnane alkaloid derivatives were obtained from
Pachysandra terminalis Sieb. et Zucc. (Buxaceae)
Several alkaloids with minor structural modifications of already known alkaloids have been reported. Wu et al. (2022) [
108] reports new aglain derivatives (
62), isolated from
Aglaia odorata Lour. However, the structural differences from the already reported aglain derivatives were the absence of methoxy’s. These compounds exhibited cytotoxic activities on human leukemia cells (HEL) and human breast cancer cells with IC
50 values in the range of 0.03–8.40 μM.
A new farnesylindole alkaloid was obtained from the flowers of
Anomianthus dulcis (Dunal) J. Sinclair (Annonaceae) and was named (R)-3-(8’-hydroxyfarnesyl)-indole (
63) [
109]. The structure of the new compound is very similar to a known compound 3-(R)-3-(8’-hydroxyfarnesyl)-indole, differing by the presence of a hydroxyl in the new compound. According to the author, the new compound showed significant cytotoxic activity against KB cell lines.
A new phenanthroindolizidine alkaloid was obtained from the leaves of
Cryptocarya densiflora Blume (Lauraceae) and was named (R)-13aα-densiindolizidine (
64) [
110]. According to the author, the new compound exhibited binding interactions with crucial amino acid residues in the active sites of severe acute respiratory syndrome coronavirus MPro (SARS-COV-MPro). The structure of the new compound resembles that of ficuseptine D, the difference being the hydroxyl present in the new compound at C-6 instead of the methoxyl.
Six new isoquinoline alkaloids were obtained from the whole plant of
Hypecoum erectum L. (Papaveraceae) [
111]. NMR data indicated that the new compound Hyperectumine B (
65) has a similar structure to dihydrofumariline, the new compound has an acetamido group in place of the hydroxyl.
A new pyrrolofenanthridone alkaloid was obtained from the stem, root and bulb of
Crinum amabile Donn (Amaryllidaceae) and named Amabiloid A (
66) [
112]. According to the author, the new compound showed low inhibition against acetylcholinesterase. The structure of the new compound is similar to that of pratorimine, with the difference being the position of the hydroxyl in the aromatic ring.
5.4. Flavonoids
New flavonoids were obtained from the roots and rhizomes of
Notopterygium incisum C.T. Ting ex H.T. Chang (Apiaceae) and were named notoflavinols A (
50) and B, notophenitols A - E and (2R)-5,4′ -dihydroxy-7-O-[(E)-3,7-dimethyl-2,6-octadienyl]flavanone (
51) [
116]. According to the author, the carbonyl group on carbon 4, the side chain on carbon 7 and the oxygen on carbon 5 may be related to the anti-inflammatory action by inhibiting nitric oxide (NO).
Four new catechins were obtained from the aerial parts of
Dianella ensifolia (L.) Redouté (Asphodelaceae) [
117]. The 2(S)-20,40-dihydroxy-7-methoxyflavan (
52) is similar to a known compound 2(S)-3,’4’-dihydroxy-7-methoxyflavan, differing only in the position of the hydroxyl in the B ring.
Eleven new flavonostilbenes were obtained from the stem of
Rhamnoneuron balansae (Drake) Gilg (Thymelaeaceae) and named rhamnoneuronal D - N [
118]. According to the author, the compound rhamnoneuronal D (
54) was shown to be a potential anti-aging agent in in vitro results for sirtuin 1 (SIRT1).
A new biflavonoid was isolated from the leaves of
Schinus polygama (Cav.) Cabrera (Anacardiaceae) and named luteolin-(6→8’’)-apigenin (
55), showing anti-inflammatory activity through its membrane-stabilizing effect on erythrocytes [
119]. The new compound is similar to agathisflavone, differing by the presence of luteolin in the new compound instead of apigenin.
A new flavonoid called 4′-hydroxy-7-O-(4-hydroxybenzyl)-3-methoxy-6-prenylflavone (
57) was isolated from the leaves of
Apocynum venetum L. (Apocynaceae) [
120]. According to the author, the new compound exhibited moderate inhibitory action on NO production.
Ten new flavonoid derivatives were obtained from the fruits of
Paulownia tomentosa (Thunb.) Steud. (Paulowniaceae) [
121]. According to the author, among the compounds Paulodiplacol A (
58) showed better anti-inflammatory activity by decreasing the action of NF-κβ after addition of LPS. The new compound is similar to a known compound called paulodiplacone A (
59), differing by the presence of an extra hydroxyl at C-ring.
Two new C-benzylated chalcones were obtained from the twigs and leaves
of Caesalpinia digyna Rottler (Fabaceae) and were identified as 2′,4′-dihydroxy-3′-(2- hydroxylbenzyl) chalcone and 2′,4′-dihydroxy-5′-(2-hydroxybenzyl) chalcone (
59) [
122]. Both compounds showed cytotoxicity against SMMC-7721, A-549 and MDA-MB-231 cell lines. Compound
59 is similar to a compound known as 2’,4’-Dihydroxy-3’-(2-hydroxybenzyl)-6’-methoxychalcone, with one change of methoxyl to hydroxyl in the new compound.
A new flavonoid was obtained from the aerial parts of
Polygonum tinctorium Aiton (Polygonaceae) and was identified as 3,5,3′,4′-Tetrahydroxy-6,7-methylendioxyflavone-3-O-β-
ᴅ-glucopyranoside (
60) [
123].
Two new compounds were isolated from the whole plant of
Centella asiatica (L.) Urb. (Apiaceae) and were identified as 4′-hydroxyl-7-methoxyl-6-prenyl-3-O-trans-p-coumaroyl-flavonol (61) and (2R,3R,2′′S)-3-furanoyl-brosimacutin E (
62) [
124]. According to the author, both molecules exhibited high cytotoxic activity in HepG2 and SGC-7901 cells.
A new isoflavonoid was obtained from the bark and roots of
Ochna kirkii Oliv. (Ochnaceae) and named kirkinone A (
63) [
125]. The structural difference with the well-known compound lophirone A is an aromatic ring less in the new compound. The author also reported a new biflavonoid kirkinone B (
64), similar to a known compound 4,4′,7-tri-O-methylisocampylospermone A, the difference being the presence of methoxyls instead of hydroxyls.
A new chromenoflavanone was obtained from the fruits of
Cullen corylifolium (L.) Medik. (Ericaceae) and named corylifol H (
65) [
126]. The new compound showed dose-dependent inhibition of NO in LPS-activated RAW 264.7 macrophages. The structure of the new molecule is similar to that of an already known compound 7,8-dihydro-8-(4-hydroxyphenyl)-2,2-dimethyl-2H,6Hbenzo [1,2-b:5,4-b’]dipyran-6-one, the difference being the presence of an extra hydroxyl.
New flavonoids were obtained from the aerial parts of
Penthorum chinense Pursh (Penthoraceae) and named Penthorumside A - C [
127] (Zhao et al., 2021). The structure of the compound Penthorumside B (
66) is similar to the known compound Pinocembrin-7-O-[3’’-O-galloyl-4”,6”- hexahydroxydiphenoyl]-b-glucose, differing by the position of the galloyl group.
Polyoxygenated flavonoids were obtained from the aerial parts of
Blumea eriantha DC (Asteraceae) and determined as 3, 3’, 4’-trihydroxy-6, 7, 8-trimethoxy flavone (
67) with antiproliferative activity in NCI-H23 cell lines [
128].
Flavonoids are notably the compounds with the fewest structural innovations. The new compounds mainly change from the known ones by the location of groups, the exchange of hydroxyls for methoxyls (and vice versa) or the presence of a sugar different from the one already found.
5.5. Coumarins
Coumarins are recurring compounds in various plants, but they can also be found in fungi and bacteria. Their chemical structure consists of an organic heterocyclic, fused to a benzo-α-pyrone ring, divided into subclasses such as furanocoumarins, phenylcoumarins, isocoumarins, among others.
A new prenylated coumarin ester was obtained from the leaves, fruits and twigs of
Glycosmis ovoidea Pierre (Rutaceae) and identified as 1-(7-methoxy-2-oxo-2H-chromen-8-yl)-3-methyl-1-oxobut-2-en-2-yl (S)-2-methylbutanoate (
93) [
129].
A new coumarin was obtained from the roots of
Calophyllum pisiferum Planch. & Triana (Calophyllaceae) and was named calopisifuran (
95) [
130]. According to the author, the new compound showed significant cytotoxicity against the MDA-MB-231 cell line.
New coumarolignans were obtained from the roots of
Waltheria indica L. (Malvaceae) and were named walthindicins A-F [
131]. According to the author, among the new compounds, walthindicin A (
96) exhibited the greatest inhibition of reactive oxygen species (ROS) and showed dose-dependent inhibition of the NF-κβ transcription factor in human embryonic kidney 293 cells (Luc-HEK-293).
Coumarin derivatives similatly to xanthumol were obtained from the whole plant of
Spermacoce latifolia Aubl. (Rubiaceae) and identified as 2-acetyl-4-hydroxy-6H-furo[2,3-g]chromen-6-one (
97) and 2-(1’,2’- dihydroxypropan-2’-yl)-4-hydroxy-6H-furo[2,3-g]chromen-6-one [
132]. The authors also reported in vitro antimicrobial action of the new compounds against
Staphyloccocus aureus,
Bacillus subtilis and
Bacillus cereus.
A new coumarin was isolated from the leaves and twigs of
Murraya exotica L. (Rutaceae) and identified as 5-demethoxy-10’-ethoxyexotimarin F (
99) [
133]. According to the author, the new compound showed inhibitory activity against the enzyme monoamine oxidase B (MAO-B). The structure of the new compound resembles the known compound 10’-ethoxyexotimarin F, with the difference being the absence of the methoxy group at C-5.
A new coumarin derivative was obtained from the stem of
Ulmus elongata L.K. Fu & C.S. Ding (Ulmaceae) and named ulmuselactone A (
101) [
134]. The structure of the compound is similar to a known coumarin, except for the presence of methoxyls at C-6 and C-7 in the novel compound instead of hydroxyls.
A new isocoumarin was isolated from the bark of
Fraxinus chinensis subsp. rhynchophylla (Hance) A.E. Murray (Oleaceae) and named fraxicoumarin (
103) [
135]. The new compound showed LPS-induced NO inhibitory activity in RAW 264.7 cells.