leaf exudate of A. marlothii and Aloe rupestris showed the presence of 7-omethylaloeresin A and 5-hydroxyaloin A (Bisrat et al. 2000). Similarly, the 5-hydroxyaloin A and microstigmin A were identified from the leaf exudate of Aloe microstigma (Dagne et al. 1997). The 10-hydroxyaloin B 6′-O-acetate has been identified from the leaf exudate of Aloe claviflora (Dagne et al. 1998a). Methanolic extracts of the aloes contain several types of anthraquinones (aloesin, aloeresin A, aloeresin C, aloeresin D, aloeresin F, isoaloeresin, aloeresin E, isoaloeresin D, rabaichromone, neoaloesin A), anthrones (isorabaichromone, 2-acetonyl-7-hydroxy-8-(2-furanonyl)-7-hydroxy-5-methylchromone, 7-hydroxy-2,5-dimethylchromone 2-(carboxyethenyl)-5,7-dihydroxychromone, aloesol, aloesone, deacetyl aloesin, furoloesone, isoaloesin, 2-acetonyl-7-hydroxy-8-(3-hydroxyacetonyl)-5-methylchromone, 2-acetonyl-8-(2-furoylmethyl)-7-hydroxy-5-methylchromone, chromones (Kuo et al. 2002; Waller et al. 1978; Hutter et al. 1996; Saoo et al. 1996), and flavones (2-acetonyl-8-(2′,6′-di-O-O-coumaroyl)-glucopyranosyl-7-hydroxy-5-methylchromone, 2-acetonyl-8-(2′,caffeoyl)-glucopyranosyl-7-hydroxy-5-methylchromone, 2-acetonyl-8-(2′,cinnamoyl)-glucopyranosyl-7-hydroxy-5-methylchromone, 6′-O-coumaroylaloesin, 2′-O-tigloylaloaesin, 2′-O-feruloylaloaesin, 2′-p-O-methylcoumaroylaloesin, 7″-deoxyaloersin D, 4′-O-glucosyl-isoaloeresin DI, and 4′-O-glucosyl-isoaloeresin DII C-glycosides) were isolated from A. vera (Gomes et al. 2009; Maurya and Devasagayam 2010; Reynolds 2004; Hamman 2008; Joseph and Raj 2010; Lawrence et al. 2009; Lobine et al. 2017). The aloesin, 7-O-methylaloesin, 6-phenyl-2-pyrone-O,O-diglucoside, and aloenin B were isolated from A. rupestris (Speranza et al. 1986a,b).
The exudates of aloes (A. barbadensis, Aloe ferox, Aloe harlans, and Aloe hildebrandtii) contain several important compounds, viz protocatechuic acid, 3-furanmethanol, dihydrocoumarone, methyl-p-coumarate, pluridone, isoeleutherol, isoeleutherol-5-O-glucoside, 5-OH-3-methylnaphto(2,3-c)-furan-4(1H)-one, 3-methylnaphto(2,3-c)-furan-4(9H)-one, 3-methylnaphto(2,3-c)furan-4,9-dione, feroxidin, feroxidin A, plicataloside, feroxidin B, 7-O-methylaloesin, 7-O-methylaloesinol, 7-O-methylaloeresin A, 8[C-B-D-(2-O-(E)-cinnamoyl]glucopyranolsyl]-2-[(R)-2-hydroxypropyl]-7-methoxy-5-methylchromone, 8-C-glucosyl-noreudenin, 8-C-glucosyl-(2′-O-cinnamoyl)-7-O-methylaloediol, 8-C-glycosyl-7-O-methyl aloediol, 8-C-glycosyl-S-aloesol, and 8-C-glycosyl-7-O-methyl-S-aloesol (Levin et al. 1988; van Wyk and Smith 2008; van Wyk et al. 1995a,b; Veitch et al. 1994; Dagne et al. 2000; Ombito et al. 2015). The γ-coniceine and coniine were identified from Aloe gillilandii and Aloe viguieri (Dring et al. 1984); dihydroisorhamnetin, aloeresin D, aloeresin A (2′-O-p-coumaroylaloesin), aloesol, aloesin, aloesone, 2′-O-tigloylaloesin, isoeleutherol, 10-hydroxyaloin B, N-methyltyramine, O,N-dimethyltyramine, 5-hydroxyaloin A, chrysophanol anthrone, aloe emodin, aloin A/B, aloinoside A/B, naringenin, apigenin, isovitexin, and aloe emodin anthrone from Aloe spp. (Holdsworth 1972; Sigler and Rauwald 1994; Rauwald and Lohse 1992; Rauwald et al. 1989; Manitto et al. 1990; Reynolds 1985; Rauwald and Beil 1993; Nash et al. 1992; Speranza et al. 1986a; Makino et al. 1974; Conner et al. 1990a,b; Hay and Haynes 1956; Horhammer et al. 1964; Dagne et al. 1994, 1996, 1997; Viljoen et al. 1998; Haynes et al. 1970); aloe-emodin-11-O-rhamnoside, rabaichromone, and aloe-emodin-10-C-rhamnoside from Aloe rabaiensis (Conner et al. 1989); 6′-O-coumaroylaloesin from Aloe castanea (van Heerden et al. 2000); neoaloesin A, isorabaichromone, isoaloesin, isoaloeresin D, deacetylaloesin, aloeresin E, 8-C-glucosyl-noreugenin 8-C-glucosyl-(8)-aloesol, 8-C-glucosyl-7-O-methyl-(8)-aloesol, 8-C-glucosyl-7-O-methylaloediol, 8-C-glucosyl-(2′-O-cinnamoyl)-7-O-methyl-aloediol A, 8-C-glucosyl-(2′-O-cinnamoyl)-7-O-methyl-aloediol B, 4′-O-glucosyl-isoaloeresin DI, and 4′-O-glucosyl-isoaloeresin DII from A. vera (van Heerden et al. 1996; Okamura et al. 1996a,b, 1997, 1998; Park et al. 1996); dihydroisocoumarin glucoside from A. hildebrandtii (Veitch et al. 1994); 7-O-methylaloesin from A. rupestris (Bisrat et al. 2000); 7-O-methylaloesinol from Aloe capensis (Park et al. 1997); nataloin A/B, aloenin (Aloecarbonoside), aloenin aglycone, and aloenin-2″-p-O-coumaroyl ester from Aloe nyeriensis (Suga et al. 1974; Conner et al. 1987); and chrysophanol-8-methyl ether, protocatechuic acid, and aloechrysone have been identified from Aloe berhana (Dagne and Alemu 1991; Dagne et al. 1991, 1992). Nataloin and 7-hydroxyaloin have been isolated from latex of Aloe pulcherrima and demonstrated antimalarial activity in a dose-independent manner (Teka et al. 2014, 2016; Bbosa et al. 2013); asphodelin, bianthracene II–IV, aloesaponol IV-8-O-glucoside, aloesaponol III-8-O-glucoside, aloesaponol I-6-O-glucoside, aloesaponol II-6-O-glucoside, aloesaponol I, aloesaponarin I, aloesaponol II–IV, laccaic acid D methyl ester, isoeleutherol-5-O-glucoside, isoxanthorin, helminthosporin, desoxyerythrolaccin, aloesaponarin II, and chrysophanol from Aloe saponaria (Yagi et al. 1974, 1977a,b, 1978, 1983; Snider and Zhang 1993), 2′-p-O-methylcoumaroylaloesin, and 1,5-dihydroxy-3-hydroxymethylanthraquinone from Aloe excelsa (Mebe 1987); 7-hydroxyaloin-6′-O-monoacetate A/B, 7-hydroxyaloe-emodin, 7-hydroxyaloin-4′,6′-O-diacetate A/B from Aloe succotrina (Sigler and Rauwald 1994; Rauwald and Diemer 1986); nataloe-emodin and nataloe-emodin-2-O-glucoside from A. nyeriensis (Conner et al. 1987); nataloe-emodin-8-methyl ether from Aloe speciosa (Thomson 1987); campesterol, cholesterol, lupeol, bisbenzopyran, 8-[C-β-D-[2-O-(E)-cinnamoyl]glucopyranosyl]-2-[(R)-2-hydroxypropyl]-7-methoxy-5-methylchromone, 6′-O-p-coumaroyl-7-hydroxylaloin A/B, 7-hydroxyaloin A/B, 6′-O-cinnamoyl-8-O-methyl-7-hydroxylaloin A/B, 8-O-methyl-7-hydroxylaloin A/B, aloesaponol IV-4-O-glucoside, aloe barbendol, aloesaponol IV, 7″-deoxyaloeresin D, O-demethyl,4-O-glucoside and aloesaponol IV- O-demethyl, 4-O-glucoside from A. barbadensis (Rauwald 1990; Yagi et al. 1998; Saleem et al. 1997a,b; Rauwald and Voetig 1982; Haynes et al. 1960; Hutter et al. 1996; Saleem et al. 1997a,b); prechrysophanol from Aloe graminicola (Yenesew et al. 1993); eigonicardine (elgonica-dimers A and B) from Aloe elgonica (Conner et al. 1990b); 7-O-methylaloeresin A and 5-hydroxyaloin A 6′-O-acetate from A. marlothii (Bisrat et al. 2000); microstigmin A from A. microstigma (Dagne et al. 1997); 10-hydroxyaloin B 6′-O-acetate from A. claviflora (Dagne et al. 1998a,b); littoraloside, littoraloin, and deacetyllittoraloin from Aloe littoralis (Dagne et al. 1996, 1998b; Viljoen et al. 1996); (E)-2-acetonyl-8-(2′-O-cinnamoyl)-β-D-glucopyranosyl-7-methoxy-5-methylchromone, (E)-2-acetonyl-8-(2′-O-caffeoyl)-β-D-glucopyranosyl-7-methoxy-5-methylchromone, and 6′-O-cinnamoyl-5-hydroxyaloin A from Aloe broomii (Holzapfel et al. 1997); microdontin A/B from Aloe microdonta (Farah et al. 1992); homonataloin A/B from Aloe jacksonii (Conner et al. 1990a; Haynes et al. 1960); homonataloside B from Aloe lutescens (van Heerden et al. 2000; Viljoen et al. 2002); 2-(carboxyethenyl)-5,7-dihydroxychromone from Aloe cremnophila (Conner et al. 1990a); aloenin B, isoaloeresin A, aloeresin C, 2-acetonyl-7-hydroxy-8-(3-hydroxyacetonyl)-5-methylchromone, 2-acetonyl-8-(2-furoylmethyl)-7-hydroxy-5-methylchromone, CA-14 [benzo(f)chroman-3-one (process product)], feralolide, 7-hydroxy-2,5-dimethylchromone, CA-12 (1,1-diphenylethane derivative), and feroxin A and B from Cape and Kenya aloe (Speranza et al. 1985, 1986b, 1988, 1990, 1993a,b, 1994, 1996, 1997); β-sitosterol,4″,6″-ethylidene-aloenin, aloenin acetal, 3-furanmethanol, 2′-O-feruloylaloesin, and dihydrocoumarone (2,3-dihydrobenzofuran) from A. arborescens (Woo et al. 1994; Makino et al. 1974; Yamamoto et al. 1991); plicataloside from Aloe plicatilis (Wessels et al. 1996); pluridone from Aloe pluridens (Confalone et al. 1983); aloeresin E and aloeresin F from Aloe peglerae (van Heerden et al. 1996); (E)-2-acetonyl-8-(2′,6′-di-O,O-coumaroyl)-β-D-glucopyranosyl-7-hydroxy-5-methylchromone from A. speciosa (Holzapfel et al. 1997); (E)-2-acetonyl-8-(2′-O-feruloyl)-β-D-glucopyranosyl-7-methoxy-5-methylchromone from Aloe africana (Holzapfel et al. 1997); methyl-p-coumarate, feroxidin, 5-OH-3-methylnaphto[2,3-c]furan-4(1H)-one, 5-OH-3-methylnaphto[2,3-c]furan-4(9H)-one, and 5-OH-3-methylnaphto[2,3-c]furan-4,9-dione from A. ferox (Speranza et al. 1990; Koyama et al. 1994).
The
