2.2.1. Orobanche Sectio Orobanche (=sect. Osproleon Wallr. = Genus Orobanche L. s.str.)
Orobanche alba Stephan ex Willd.—Roudbaraki and Nori-Shargh identified forty different compounds in the essential oil from
O. alba [province of Guilan, Iran; aerial parts; hydrodistillation; GC, GC-MS, comparison with authentic samples] [host species not mentioned] [
11]. Detected compounds included three monoterpene hydrocarbons, twelve oxygenated monoterpenes, five sesquiterpene hydrocarbons, three oxygenated sesquiterpenes, one oxygenated diterpene, and sixteen non-terpenic compounds (aliphatic hydrocarbons, alcohols, ethers, aldehydes, ketones, carboxylic acids, and esters). The monoterpene fraction encompassed bornylangelate,
p-cymene, limonene, γ-terpinene,
p-menthone, 1,8-cineol, pinocamphone, linalool, (
Z)-iso-citral, nerol, neral (syn. citral B,
cis-isomer), geraniol, geranial (syn. citral B,
trans-isomer), and geranylacetate; the sesquiterpene fraction included
trans-caryophyllene (syn. β-caryophyllene), 6,9-guaiadiene, isobornyl-2-methyl-butyrate, δ-cadinene α-copaene, β-bourbonene, and caryophyllene oxide. The only diterpene detected was manool and the only phenylpropanoid methyl chavicol (syn. estragol). Detected non-terpene compounds comprised
n-nonanal, neryl acetate, myristic acid, palmitic acid, linoleic acid, linolenic acid, 6-methyl-5-hepten-2-one, 6,10,14-trimethyl-2-pentadecanone, octadecane, heneicosane, docosane, tricosane, tetracosane, pentacosane, nonadecene, isobutyl phthalate, and bis(2-ethylhexyl)phthalate. Fruchier et al. reported the isolation of the tropone derivative orobanone (
45) from
O. alba (as
O. epithymum DC.) [whole plants; water, chloroform; IR, UV, MS, CI-MS,
1H and
13C NMR] [host species not mentioned] [
12].
Orobanche amethystea Thuill.—In
O. amethystea Serafini et al. [Sardinia, Italy; flowering plants; alcoholic extract;
1H and
13C NMR, HPLC, co-elution of extracts with isolated and identified phenylpropanoid glycosides] [host species not mentioned] detected the phenylpropanoid glycosides verbascoside (syn. acteoside, orobanchin, [
13]) (
10) and oraposide (syn. crenatoside and orobanchoside) (
29) [
14].
Orobanche anatolica Boiss. & Reut.—The occurrence of saponins in
O. anatolica was mentioned by Aynehchi et al. [Iran; whole plant] [host species not mentioned] but no further specification of structures nor of any analytical methods were indicated in the report [
15].
Orobanche artemisiae-campestris Gaudin subsp. picridis (F.W.Schultz) O. Bolòs, Vigo, Masalles & Ninot—Fruchier et al. isolated the tropone derivative orobanone (
45) [whole plant; water, chloroform; IR, UV, MS, CI-MS,
1H and
13C NMR] [no information about the host] from
O. artemisiae-campestris subsp.
picridis (using the synonym
O. picridis F.W.Schultz) [
12].
Orobanche caryophyllacea Sm.—The tropone derivative orobanone (
45) was isolated from
O. caryophyllacea (using the synonym
O. major L.) by Fruchier et al. [whole plant; water, chloroform; IR, UV, MS, CI-MS,
1H and
13C NMR] [no information about the host] [
12].
Orobanche cernua Loefl.—Qu et al. characterized 17 compounds from
O. cernua (syn.
O. cumana Wallr.,
O. cernua var. cumana Wallr.) [Jilin province, China; fresh whole plants; methanol; MS, 1D and 2D NMR, comparison with literature data] [host species not mentioned] [
17]. Eleven compounds were identified as phenylpropanoid glycosides [salidroside (
8), acteoside (
10), 2′-
O-acetylacteoside (
14), campneoside (
18), leucosceptoside A (
19), isoacteoside (
23), isocampneoside (
24), oraposide (
29), 3‴-
O-methylcrenatoside (
30), descaffeoyl crenatoside (
31), and isocrenatoside (
32)]. Furthermore, three phenolic acids [caffeic acid (
34),
trans-ferulic acid (
36), and chlorogenic acid (
37)], one lignan [dimethyl-6,9,10-trihydroxybenzol[
kl]xanthene-1,2-dicarboxylate (
38)], and two flavonoids [apigenin (
42) and luteolin (
43)], were found. In a second report Qu et al. described the isolation of a novel phenylethanoid glycoside, 3′-
O-methylisocrenatoside (
33) as well as of the known compounds protocatechuic aldehyde (
2) and methyl caffeate (
35) from
O. cernua [Jilin Province, China; fresh whole plant; methanol; IR, MS, NMR] [host species not mentioned] [
18]. Yang et al. examined
O. cernua [Neimenggu province, China; whole plant; ethanol 70%, reflux; HPLC-MS, NMR] [host species not mentioned] isolating twelve compounds: eight phenylpropanoid glycosides [acteoside (
10), campneoside II (
17), campneoside I (
18), leucosceptoside A (
19), isoacteoside (
23), cistanoside F (
27), oraposide (
29), and isocrenatoside (
32)]; three lignans [(+)-pinoresinol 4′-
O-β-
D-glucopyranoside (
39), isoeucommin A (
40), and (+)-syringaresinol 4′-
O-β-
D-glucopyranoside (
41)], and one steroid [stigmasterol 3-
O-β-
D-glucoside (
54)] [
19].
Orobanche coerulescens Stephan ex Willd.—Zhao et al. isolated the phenylpropanoid glycoside acteoside (
10) from
O. coerulescens [Xinjiang province, China; ethanol] [host species not mentioned] [
20]. The isolation of isoacteoside (
23), sinapoyl 4-
O-β-
D-glucoside (
26), cistanoside F (
27), oraposide (
29), and adenosine was described in a second report [
21] [Xinjiang province, China; rhizome; ethanol 95%, reflux; TLC, NMR] [host species not mentioned]. Acteoside (
10), cistanoside F (
27), and oraposide (
29) were also isolated by Murayama et al. along with 2-phenylethyl β-primeveroside (
7), rhodioloside (syn. salidroside) (
8), descaffeoyl crenatoside (
31), and isocrenatoside (
32) from
O. coerulescens [Niigata prefecture, Japan; whole plant; methanol; IR, UV, HR-FAB-MS,
1H,
1H-DQF, COSY,
1H,
1H-relayed COSY, HMQC, and HMBC NMR] [host species not mentioned] [
22]. Lin et al. isolated two new phenylpropanoid glycosides, caerulescenoside (
13) and 3′-methyl crenatoside (
30), along with five known phenylpropanoid glycosides, desrhamnosyl acteoside (
9), acteoside (
10), campneoside (
18), isoacteoside (
23), and oraposide (
29) from
O. coerulescens [Taipei, Taiwan; whole plant; ethanol 95%; IR, UV,
1H NMR,
13C NMR, ESI-MS, FAB-MS, HR-FAB-MS] [host species not mentioned] [
23]. In a second report the authors mentioned the occurrence of another phenylpropanoid glycoside, rossicaside B (
28), in
O. coerulescens; ethanol 95%, preparation in accordance with former report, no information about analytical methods) [
24]. Wang et al. also isolated a new phenylpropanoid glycoside from the whole plant of
O. coerulescens [Neimenggu province, China; whole plant; ethanol 50%; TLC, HPLC, MS, NMR] [host species not mentioned] [
25]. The structure was identified as 2-(3-methoxy-4-hydroxy)-phenyl-ethanol-1-
O-α-L-[(1→3)-4-
O-acetyl-rhamnopyranosyl-4-
O-feruloyl]-
O-β-
D-glucopyranoside and named orobancheoside A (
22). Additionally, Zhao et al. described the isolation protocatechuic aldehyde (
2) and caffeic acid (
34) as well as of β-sitosterol (
50) and daucosterol (
53) from
O. coerulescens [Xinjiang province, China; rhizome; ethanol 95%, reflux; NMR] [host species not mentioned] [
26]. Shao et al. identified the phenylpropanoid glycosides acteoside (
10) and oraposide (
29), as well as sterols β-sitosterol (
50), stigmasterol (
51), and β-daucosterol (
53) [Neimenggu province, China; ethanol 95%, reflux; TLC, MS, NMR] [host species not mentioned] [
27]. Moreover, primary metabolites D-mannitol, glyceryl arachidate, succinic acid, and D-pinitol were reported. Recently, Zhang characterized a new phenethyl alcohol glycoside named orobancheoside B (
21) from
O. coerulescens [Neimenggu province, China; whole plant; ethanol 50%; IR, UV, MS, NMR] [host species not mentioned] [
28].
Orobanche crenata Forssk.—El-Shabrawy et al. found two phenylpropanoid glycosides in
O. crenata growing on
Vicia faba L. [Egypt; chloroform for removal of non-polar compounds, aqueous ethanol 70%; TLC, NMR] [
29]. However, their structures were not fully characterized. Afifi et al. extracted secondary metabolites from
O. crenata parasitizing on
V. faba [Mansoura, Egypt; aerial parts; ethanol 90%; melting point, TLC, IR, UV,
1H NMR,
13C NMR,
13C NMR-DEPT, FAB-MS] and isolated the known phenylpropanoid glycoside acteoside (
10) as well as the new phenylpropanoid glycoside oraposide (
29) [
30]. Acteoside (
10) was also extracted by Gatto et al. [parasitizing on
V. faba; Apulia, Italy; stems; methanol 80% under reflux; comparison of UV spectra and retention times with standard substances, HPLC-DAD] who furthermore found isoverbascoside (syn. isoacteoside; an isomer of verbascoside) (
23) and an unidentified caffeic acid derivative [
31,
32,
33]. Serafini et al. isolated verbascoside (
10), poliumoside (
11), and orobanchoside (
29) from
O. crenata [Sardinia, Italy; flowering plants; alcoholic extract;
1H and
13C NMR, HPLC, co-elution of extracts with isolated and identified phenylpropanoid glycosides] [host species not mentioned] [
14]. Orobanchoside (
29) was proven to be structurally identical with oraposide and oraposide by Nishibe et al. in the same year [
34]. Nada and El-Chaghaby analyzed ethanolic (80%) extracts of
O. crenata grown on
V. faba by GC-MS and postulated the occurrence of 6-monohydroxyflavone, glycitein, actinobolin, hexestrol, and 2,4-di-tert-butylphenyl benzoate [Egypt; ethanol 80%; GC-MS] [
35]. However, none of these compounds are considered any further here, because the data on the used GC system are incomplete and data on peak identification procedures are completely missing. Until contrary evidence will have been procured, we do not consider 6-monohydroxyflavone, glycitein, actinobolin, hexestrol, and 2,4-di-tert-butylphenyl benzoate natural products which have been detected in the genus
Orobanche. Dini et al. investigated the phytochemistry of
O. crenata using the synonym
O. speciosa DC. [Molise, Italy; aerial parts; petroleum ether, chloroform, methanol; comparison of UV, IR,
1H and
13C NMR spectral data with literature data] [
36]. The three phenylpropanoid glycosides verbascoside (
10), poliumoside (
11), and oraposide (
29) were detected. Along with these compounds the authors also isolated
p-hydroxy benzaldehyde (
1), isovanillin (
3), vanillin (
4), syringaldehyde (
5), and
p-hydroxy acetophenone (
6). Fruchier et al. reported the isolation of the tropone derivative orobanone (
45) from
O. crenata in their investigation of the occurrence of this secondary metabolite in various
Orobanche species [whole plant; water, chloroform; IR, UV, MS, CI-MS,
1H and
13C NMR] [host species not mentioned] (see extra paragraph and
supplementary material) [
12]. Abbes et al. described the extraction of polyphenols and tannins from
O. crenata growing on
V. faba without any further specification of the substances [Beja and Ariana Governorates, Tunisia; aerial parts; methanol; water] [
37].
Orobanche denudata Moris—Serafini et al. isolated the phenylpropanoid glycosides verbascoside (
10) and orobanchoside (
29) from
O. denudata [Sardinia, Italy; flowering samples; alcoholic extract;
1H and
13C NMR, HPLC, co-elution of extracts with isolated and identified phenylpropanoid glycosides] [host species not mentioned] [
14].
Orobanche foetida Poir.—Abbes et al. described the extraction of polyphenols and tannins from
O. foetida growing on
V. faba without any further specification of the substances [Beja and Ariana Governorates, Tunisia; aerial parts; methanol; water] [
37].
Orobanche gracilis Sm.—Fruchier et al. isolated the tropone derivative orobanone (
45) from
O. gracilis (using the synonym
O. cruenta Bertol.) [whole plants; water, chloroform; IR, UV, MS, CI-MS, and
1H and
13C NMR] [no information about the host] [
12].
Orobanche grisebachii Reut.—Aynilian et al. screened several
Orobanche species for their contents of alkaloids, tannins, and saponins, without reporting any particular structures of the metabolites.
O. grisebachii [plant material obtained from The Post Herbarium of the American University of Beirut, Lebanon; ethanol 95%, ethanol 80%] contained alkaloids and tannins [
40].
Orobanche hederae Duby—Pieretti et al. isolated the phenylpropanoid verbascoside (
10) and orobanchoside (
29) from
O. hederae [Lazio, Italy; whole plants; ethanol;
1H NMR, HPLC-UV] [host species not mentioned] [
41]. Capasso et al. also found these two compounds [whole plants; ethanol] [host species not mentioned] [
42]. As well as in eleven other species of the genus
Orobanche (see extra paragraph) Fruchier et al. found the tropone derivative orobanone (
45) in
O. hederae [whole plant; water, chloroform; IR, UV, MS, CI-MS,
1H and
13C NMR] [host species not mentioned] [
12]. Baccarini and Melandri isolated and analyzed seven pigments from
O. hederae growing on
Hedera helix L. (Araliaceae) [whole plant; acetone 80%; TLC, comparison with standard substances]. These pigments were β-carotene, α-carotene-5,6-epoxide, flavochrome, lutein-5,6-epoxide, flavoxanthin, and taraxanthin [
43]. The seventh compound was tentatively identified as neoxanthin. There is also a report of the sequestration of substances from its host species by
O. hederae. This is described in a separate paragraph below.
Orobanche loricata Rchb.—The isolation of the phenylpropanoid glycosides verbascoside (
10) and orobanchoside (
29) from
O. loricata was described by Serafini et al. [Sardinia, Italy; flowering samples; alcoholic extract;
1H and
13C NMR, HPLC, co-elution of extracts with isolated and identified phenylpropanoid glycosides] [host species not mentioned] [
14]. Fruchier et al. isolated the tropone derivative orobanone (
45) [whole plants; water, chloroform; IR, UV, MS, CI-MS,
1H and
13C NMR] [no information about the host] [
12].
Orobanche lutea Baumg.—Rohmer et al. analyzed several parasitic species for their sterol contents and sterol biosynthesis [
44]. The following compounds were isolated and identified from
O. lutea [Alsace, France; stems; acetone, chloroform:methanol (2:1); GLC, GLC-MS] [host species not mentioned]: sterols [stigmastanol (
46), cholesterol (
47), campesterol (
48), 24-methylene cholesterol (
49), sitosterol (
50), stigmasterol (
51),
isofucosterol (
52), ∆
7-campestenol (
55), episterol (
56), ∆
7-stigmastenol (
57), and ∆
7-avenasterol (
58)], 4α-methylsterols [24- 24-methyl lophenol (
59), methylene lophenol (
60), 24-ethyl lophenol (
61), 24-ethylidene lophenol (
62), 4α-methyl ∆
8-campestenol (
63), 4α-methyl ∆
8-stigmastenol (
64), 24,28-dihydro obtusifoliol (
65), obtusifoliol (
66), 24,28-dihydrocycloeucalenol (
67), cycloeucalenol (
68), and 4,4-dimethylsterols cycloartenol (
69)], and 24-methylene cycloartenol (
70).
Orobanche minor Sm.—Kurisu et al. isolated the phenylpropanoid glycosides acteoside (
10) and oraposide (
29) from
O. minor [whole plant; methanol; NMR (
1H,
13C, COSY, HMQC, HMBC, NOESY), HR-ESI-MS] [host species not mentioned] [
45]. Serafini et al. also extracted verbascoside (
10) and orobanchoside (
29) [Sardinia, Italy; flowering samples; alcoholic extract;
1H and
13C NMR, HPLC, co-elution of extracts with isolated and identified phenylpropanoid glycosides] [host species not mentioned] [
14]. Kidachi et al. isolated acteoside (
10), cistanoside D (
20), isoacteoside (
23), oraposide (
29), 3‴-
O-methyl crenatoside (
30), and isocrenatoside (
32) [whole plant; methanol] [host species not mentioned] [
46]. The tropone derivative orobanone (
45) was found in
O. minor by Fruchier et al. [whole plant; water, chloroform; IR, UV, MS, CI-MS,
1H and
13C NMR] [host species not mentioned] [
12].
Orobanche owerinii Beck—Dzhumyrko and Sergeeva detected several carotenoids in
O. owerinii [epigeal parts;
n-hexane, petrol ether; co-chromatography with reference compounds and UV spectroscopy] growing on the hypogeal organs of
Fraxinus [
47]. Violaxanthin, auroxanthin, the ester of violaxanthin and palmitic acid, as well as α- and β- carotenes were detected.
Orobanche pubescens d´Urv.—Aynilian et al. screened several
Orobanche species for their contents of alkaloids, tannins, and saponins, without investigating any particular structures of the metabolites. Tannins were found in
O. pubescens (using the synonym
O. versicolor F.W.Schultz) [plant material obtained from The Post Herbarium of the American University of Beirut, Lebanon; petroleum benzine (defatting), ethanol 95%, ethanol 80%] [
40].
Orobanche pycnostachya Hance—Han et al. isolated eight compounds from
O. pycnostachya [Neimenggu province, China; ethanol 95%; MS, NMR] [host species not mentioned] [
48]. The primary metabolites
n-nonacosane acid,
n-hexacosyl alcohol,
D-allitol, 2,3,4,6-α-
D-galactopyranose tetramethyl ether, and secondary metabolites acteoside (
10), fissistigmoside (
25), β-sitosterol (
50), and daucosterol (
53) were identified. Li et al. also isolated the phenylpropanoid glycosides acteoside (
10) as well as 2′-
O-acetylacteoside (
14), and oraposide (
29) [Mengu, Anhui and Hebei, China; methanol 70%; HPLC] [host species not mentioned] [
49].
Orobanche rapum-genistae Thuill.—Several secondary metabolites such as phenylproanoid glycosides, alkaloids, and a tropone derivative have been isolated from
O. rapum-genistae. The isolated alkaloids are presumably not synthesized by the parasite itself but sequestered from the host species. Sequestration of secondary metabolites by
O. rapum-genistae from its host is also reported by other authors and described in a separate paragraph below. Fruchier et al. isolated the tropone derivative orobanone (
45) from
O. rapum-genistae parasitizing on
Cytisus scoparius (L.) Link and
Cytisus purgans (L.) Spach (both Fabaceae) [whole plant; water, chloroform; IR, UV, MS, CI-MS,
1H and
13C NMR] [
12]. Eleven other
Orobanche species were also screened for orobanone (
45) (see separate paragraph and
supplementary material). Several sources report the isolation of the two phenylpropanoid glycosides verbascoside (
10) and oraposide (
29) from
O. rapum-genistae (Andary et al., [
50,
51] (host:
C. scoparius,
C. purgans), [
39] [phenolic extract; hydrolysis, high resolution
1H and
13C NMR], [
38] [
1H and
13C NMR, X-ray crystal analysis]; Bridel and Charaux, [
52,
53] [tubers/bulbs; alcohol]; Serafini et al., [
14] [Sardinia, Italy; flowering plants; alcoholic extract;
1H and
13C NMR, HPLC, co-elution of extracts with isolated and identified phenylpropanoid glycosides] [host species not mentioned]; Viron et al., [
54] [whole plant; aqueous ethanol 70%; HPTLC, HPLC] [host species not mentioned], [
55]). Andary et al. described the differentiation of two ecotypes of
O. rapum-genistae:
O. rapum-cytisi scoparii (parasitizing
C. scoparius) and
O. rapum-cytisi purgantis (parasitizing
C. purgans) based on morphological and phytochemical characteristics [
51]. Phenylpropanoid glycosides verbascoside (
10) and orobanchoside (
29) as well as quinolizidine alkaloids sparteine (
S2) and lupanine (
S4) were found in both ecotypes in different concentrations.
Orobanche sanguinea C.Presl.—Serafini et al. isolated the phenylpropanoid glycosides verbascoside (
10) and orobanchoside (
29) from
O. sanguinea [Sardinia, Italy; flowering samples; alcoholic extract;
1H and
13C NMR, HPLC, co-elution of extracts with isolated and identified phenylpropanoid glycosides] [host species not mentioned] [
14].
Orobanche variegata Wallr.—Fruchier et al. isolated the tropone derivative orobanone (
45) from
O. variegata [whole plant; water, chloroform; IR, UV, MS, CI-MS,
1H and
13C NMR] [no information about the host] [
12].