Phytochemistry, Medicinal Uses and Pharmacological Activities of Parkia: Comparison
Please note this is a comparison between Version 1 by Yusof Kamisah and Version 2 by Camila Xu.

Parkia is a genus of flowering plants belonging to the family Fabaceae (subfamily, Mimosoideae) with pan-tropical distribution. The word Parkia was named after the Scottish explorer Mungo Park, who drowned in the Niger River, Nigeria in January 1805. The genus Parkia (Fabaceae, Subfamily, Mimosoideae) comprises about 34 species of mostly evergreen trees widely distributed across neotropics, Asia, and Africa. 

  • Parkia
  • Mimosoideae
  • traditional medicine
  • secondary metabolite

1. Introduction

Parkia is a genus of flowering plants belonging to the family Fabaceae (subfamily, Mimosoideae) with pan-tropical distribution [1]. The word Parkia was named after the Scottish explorer Mungo Park, who drowned in the Niger River, Nigeria in January 1805 [2]. Thirty-one species from this genus were reported in 1995 [3]. Another four more species were discovered in 2009 [4]. Out of these species, 10 species found in Asia, four in Africa, and 20 in neotropics. Meanwhile, according to a plant list (2018), 80 scientific names are recorded from the genus Parkia containing 41 accepted names and 39 synonym species (The Plant List, 2018). These plants bear fruits called pods. Each pod contains up to 25–30 seeds. Many species from Parkia have been reported to be rich in carbohydrate [5][6][7][5,6,7], protein [8][9][10][8,9,10] and minerals [11][12][13][14][11,12,13,14].

2. Traditional Medicinal Uses

Parkia species are being used across all tropical countries to cure different ailments. Virtually, all parts of Parkia plants are utilized traditionally for different medicinal purposes. The materials of different parts of Parkia plants are processed as paste, decoction, and juice for the treatment of various ailments (Table 1). Almost all reported Parkia species are used in different forms to cure diarrhea and dysentery [15]. Different parts of P. biglobosa, P. clappertoniana, P. roxburghii, and P. speciosa are reported to be traditionally used for the treatment of diabetes [16][17][18][16,17,18]. Furthermore, skin-related diseases, such as eczema, skin ulcers, measles, leprosy, wound, dermatitis, chickenpox, scabies, and ringworm are treated using leaves, pods, and roots of P. speciosa and P. timoriana [19][20][21][19,20,21]. The stem barks of P. bicolor, P. clappertoniana, P. biglobosa, P. roxburghii as well as roots of P. speciosa are applied in the form of paste and decoction to treat different skin problems [22][23][24][25][22,23,24,25]. Decoction and paste of stem bark, pod, or root of P. biglobosa and P. speciosa are used to treat hypertension [22][26][27][22,26,27]. Moreover, stem barks of P. bicolor, P. biglobosa and leaves of P. speciosa are used for severe cough and bronchitis [28][29][30][28,29,30]. These aforementioned uses suggested that Parkia plants are likely to contain constituents with broad and diverse biological activities, such as antidiabetic, antimicrobial, antihypertensive, and anti-inflammatory.
Table 1.
The medicinal uses of plants from genus
Parkia
.
125]. In addition, some minor components, such as 8284 are also identified. Meanwhile, 132 content in P. speciosa seed was reported to be 4.15 mg/100 g [85][37], but that of P. biglobosa in a recent study was found to be much higher (53.47 mg/100 g). Phospholipid content of P. biglobosa seeds was about 451 mg/100 g [122]. The seeds also contain palmitic acid, stearic acid, oleic acid, arachidic acid, and linoleic acid, the most abundant fatty acid [22][121][130][22,121,130]. Similar fatty acids are also reported in the raw seeds of P. roxburghii chloroform/methanol extract, in addition to total free phenol (0.56 g/100 g seed flour) and tannins (0.26 g/100 g seed flour) contents [87][41].
Figure 45.
Structural formulas of cyclic polysulfides
81
93
, as previously listed in
Table 2
.

4. Pharmacological Activities of Parkia Species

Numerous bioactive constituents such as phenolics, flavonoids, terpenoids, and volatile compounds present in Parkia species may account for its various health benefits, and therefore responsible for the vast pharmacological properties (Table 3). However, only few species have been extensively studied.
Table 3.
Pharmacological activities of
Parkia species
extracts and fractions.

3. Phytochemistry of Genus Parkia

Among the numerous species of Parkia plant, the chemistry of only few are known. However, different parts of the reported ones have been validated as good sources of phenolic compounds [11][79][80][11,31,32], saponins [81][82][83][33,34,35], terpenoids [83][84][85][35,36,37], steroids [23][44][86][23,38,39], tannins [37][44][86][38,39,40], fatty acids [23][87][23,41], and glycosides [88][89][90][42,43,44]. Various phytochemicals are found in the stem barks, leaves, seeds, and pods of these plants. The stem bark of P. biglobosa is reported to contain phenols, flavonoids, sugars, tannins, terpenoids, steroids, saponins [11][44][11,38], alkaloid, and glycosides [83][89][91][35,43,45], while the leaves contain glycosides, tannins, and alkaloids in trace amount [11][23][92][11,23,46], in addition to flavonoids, phenols, and anthraquinones [93][47]. Phytochemical screening of the seeds shows the presence of saponins, alkaloids, flavonoids, polyphenols, terpenoids, glycosides and tannins [94][95][48,49]. Fermentation or roasting of P. biglobosa seeds results in the alteration of the bioactive components. P. bicolor leaves contain chemical constituents similar to that of P. biglobosa such as glycosides, tannin, and alkaloids in trace amount [23]. The stem bark of P. bicolor contains alkaloids, tannins, saponins, glycosides, flavonoids, and terpenoids [83][35], while P. biglandulosa contains tannins, saponins, and glycosides, and P. filicoidea possesses flavonoids, sugars, saponins, and tannins [96][50]. The seed of P. javanica contains flavonoid, saponins, alkaloids, terpenoids, anthraquinones, steroids, and glycosides [90][44]. The pods are reported to have tannins, flavonoids, and saponins, all of which are significantly diminished when subjected to various processing methods, such as ordinary and pressure cooking methods [75][97][51,52]. Alkaloids, glycosides, saponins, and tannins are present in the whole plant of P. clappertoniana [79][31]. Phytochemical analysis of the leaves of P. platycephala revealed the presence of phenols, terpenoids, flavonoids [98][53], tannins and saponins [99][54]. Furthermore, flavonoids, alkaloids, phenols, and terpenoids were reported to be present in all parts of P. speciosa plant [85][37]. Phytochemicals (primary and secondary metabolites) are well known for their vast medicinal benefits to plants and human [100]. The primary metabolites—such as carbohydrate, proteins, chlorophyll, lipids, nucleic, and amino acids [101][102][103][101,102,103]—are responsible for plants’ biochemical reactions such as respiration and photosynthesis [102]. The secondary metabolites are majorly alkaloids, phenols, terpenoids, flavonoids, saponins, steroids, tannins, and glycosides, which play important roles in protecting the plants against damages and improving plant aroma, coloration and flavor [101][103][101,103], The phytochemicals are present in various parts of the plants especially in the three major parts viz. the leaves, stems and roots. Their percentage composition in each plant may vary depending on environmental conditions, variety and processing methods [101]. Previous studies have shown that phenolic compounds are the most abundant and widely distributed phytoconstituents (45%), followed by steroids and terpenoids (27%), and alkaloids (18%) [101][104][101,104]. Alkaloids, flavonoids, tannins, and phenolic compounds are the most common constituents that have been studied in phytochemistry [104][105][104,105]. Several compounds from these classes have been identified and investigated from Parkia plants for various pharmacological activities. Despite the enormous reports on the phytochemical screening of different species from the genus Parkia, structure identification and purification of compounds from these species are scarcely reported compared to other genera. The compounds were identified using high-performance liquid chromatography with diode-array detector (HPLC-DAD), liquid chromatography mass spectrometry (LCMS), flow analysis-ionization electrospray ion trap tandem mass spectrometry (FIA-ESI-IT-MS), gas chromatography time-of-flight mass spectrometry (GC/ToF-MS), high-performance liquid chromatography-electrospray ion mass spectrometry (HPLC-ESI-MS), and chromatographic purification from the fraction and characterization through nuclear magnetic resonance (NMR).

3.1. Polyphenolic Compounds

Phenolic compounds found in Parkia species are grouped into simple phenol (10 and 31), phenolic acids 2941, flavone 1519 and 24, flavanone 2526, flavonol 1114 and 2022, methoxyflavonol 23, as well as flavanol 110 (Table 2). Phenolic acids are mostly found in the pods and edible parts of Parkia, while polyphenolic compounds are present in the leaves, stem barks, roots, or seeds. The most commonly reported flavonoid in Parkia species are flavanol 1 and its isomer 8, which are obtained from the pod and bark of P. speciosa and P. biglobosa, respectively [106][107][108][106,107,108] and the remaining flavanols 1118 are mainly galloylated catechins. Compound 11 is isolated from ethyl acetate fraction of P. roxburghii pod [18], while compounds 1218 are identified from the ethyl acetate fraction of root/stem of P. biglobosa [18]. One methoxyflavonol 23, two flavanone 2627 and isoflavones 2728 are identified in the edible parts of P. javanica [108]. A new flavanone, naringenin-1-4′-di-O-ß-D-glucopyranoside 26 is isolated from n–butanol fraction of P. biglobosa [109], while a new phenylpropanoid is elucidated as 4-(3-hydroxypropyl)benzyl nonanoate from the leaves of P. javanica [110]. Isolation of compounds 4243 for the first time as a pure compound was reported from the ethanol extract of P. biglobosa bark [111]. The structures of these compounds are illustrated in Figure 12 and Figure 23.
Figure 12.
Structural formulas of polyphenolics
1
28
, as previously listed in
Table 2
.
Figure 23.
Structural formulas of polyphenolics
29
46
, as previously listed in
Table 2
.
Table 2.
Phytochemical compounds from
Parkia
.

3.2. Terpenoid and Steroid

To date, few terpenoid compounds have been reported in Parkia plants. Most of these compounds were identified from barks, roots, leaves, and seeds of Parkia plants. One is monoterpenoid 50 with two of its glucosides 57 and 58, a diterpene 49, while the rest are triterpenoid 49 and 5156 (Table 2 and Figure 34). Seven out of the triterpenoids 5258 were reported as new compounds. Only 49 is reported in three species (P. biglobosa, P. bicolor, and P. speciosa). Two of the new compounds 57 and 58 are iridoid type of terpenoidal glycoside purified from methanol extract of P. javanica, together with ursolic acid and other steroidal compounds [88][42]. Compounds 5256 are isolated through different chromatographic techniques from 80% methanol extract of P. bicolor root, with a known diterpene 59 and a benzene glucoside 105. These compounds are reported to exhibit moderate antiproliferative activity with median inhibitory concentration (IC50) ranging from 48.89 ± 0.16 to 81.66 ± 0.17 µM [118].
Figure 34.
Structural formulas of terpenoids
49
59
and steroids
60
66
, as previously listed in
Table 2
.
Steroidal compounds are also reported in the genus of Parkia (Table 2 and Figure 34). β-Sitosterol (60) is one of the major components in P. speciosa [120] and P. biglobosa seeds [121]. The steroid together with stigmasterol are purified from recrystallization of chloroform/methanol fraction of P. speciosa seeds. Its composition in P. biglobosa seeds was reported to be about 377 mg/100 g dry weight [122]. It is also purified from methanol extract of P. javanica leaves [88][42]. Apart from 60, 61, and 65, which are present in P. javanica and/or P. biglobosa, all other steroids 6264 and 66 reported from different studies are found in P. speciosa seeds. Other than β-sitosterol (60), stigmasterol (61), and campesterol (65) are also among the numerous compounds identified from the seeds of P. speciosa [117][119][120][124][117,119,120,124]. The percentage composition of 60, 61, 62 and a triterpenoid 49 in the plant was reported as 3.42%, 2.18%, 2.29%, and 0.71% w/w, respectively [85][37]. In the case of P. biglobosa, the percentage composition of 60, 61 and 62 in the seeds is higher with values of 55.7%, 3.42%, 37.1% for the unfermented, and 56.8%, 3.38%, 35.9% for the fermented, respectively, indicating that fermentation process may lower 61 and 62, but increases 60 contents [129]. Meanwhile, Akintayo (2004) had recorded 60 as the most abundant compound in P. biglobosa seeds, constituting approximately 39.5% w/w. Compound 60 was isolated as a pure compound through column chromatographic separation of benzene fraction of P. bicolor leaves [88][42].

3.3. Miscellaneous Compounds

In addition to polyphenolic and terpenoids, several other compounds that are mainly volatile including aldehydes, esters, pyrazines, ketones, fatty acids, benzenes, alcohols, amines, sulfides, alkanes, and alkenes have been reported from Parkia species (Table 2). These compounds are identified mainly from the seeds. Compound 81 is identified from the natural product for the first time in pentane/dichloromethane fraction of P. speciosa seed using GC/ToF-MS [125]. A greater number of these compounds is identified through phytochemical quantification using different spectroscopic methods. Seven constituents are detected from the fresh seeds of P. speciosa through GC/ToF/MS and the compounds are dominated by linear polysulfide, alcohol, and 3′-thiobis-didodecyl ester. Other major compounds include palmitic acid, arachidonic acid, linoleic acid, linoleic acid chloride, and myristic acid [124]. However, cyclic polysulfides are the major constituents found in cooked P. speciosa seeds (Figure 45) [