Quantitative Determination of Alkaloids in Lotus Flower (Flower Buds of Nelumbo nucifera) and Their Melanogenesis Inhibitory Activity

Natural aporphine alkaloids: A comprehensive review of phytochemistry, pharmacokinetics, anticancer activities, and clinical application

BACKGROUND

Cancer is the most common cause of death and is still a serious public health problem. Alkaloids, a class of bioactive compounds widely diffused in plants, especially Chinese herbs, are used as functional ingredients, precursors, and lead compounds in food and clinical applications. Among them, aporphine alkaloids (AAs), as an important class of isoquinoline alkaloids, exert a strong anticancer effect on multiple cancer types.

AIM OF REVIEW

This review aims to comprehensively summarize the phytochemistry, pharmacokinetics, and bioavailability of seven subtypes of AAs and their derivatives from various plants and highlight their anticancer bioactivities and mechanisms of action. Key Scientific Concepts of Review. The chemical structures and botanical diversity of AAs are elucidated, and promising results are highlighted regarding the potent anticancer activities of AAs and their derivatives, contributing to their pharmacological benefits. This work provides a better understanding of AAs and combinational anticancer therapies involving them, thereby improving the development of functional food containing plant-derived AA and the clinical application of AAs.

Development of gummy bear supplements and in vitro exploration of antioxidant and antiproliferative potential of Nuciferine

BACKGROUND

Nuciferine's extensive therapeutic potential, including its robust antioxidant properties, is explored in response to the growing consumer preference for value-added organic foods.

OBJECTIVE

This study focuses on the formulation of gummy bear supplements fortified with nuciferine from Nelumbonucifera. The research highlights nuciferine's ability to combat oxidative stress induced by reactive oxygen species (ROS) and examines its application in maintaining basal ROS levels during oxidative stress conditions in skin melanoma cells.

METHODS

Characterization of extracted nuciferine through FTIR and UV-vis spectroscopy ensures product quality, while sensory evaluation compares honey and sugar as natural sweeteners for optimal flavor and consumer preference. SK-Mel-28 cellular ROS levels were measured using 2',7' -dichlorofluorescin diacetate dye before and after nuciferine treatment. SK-Mel-28 cell viability and dose response of nuciferine treatment was assessed using MTT assay.

RESULTS

Nuciferine shows potent inhibition of SK-Mel-28 cell proliferation with an IC50 of 39.31 ± 5.280 μg/ml and showed no cytotoxicity in normal L6 skeletal muscle cells. This study compares the sensory properties of honey and sugar based gummy bear formulations.

CONCLUSION

This project aims to create a high-quality, health-promoting dietary supplement that aligns with the evolving trends in organic nutrition and antioxidant supplementation.

Aromatase inhibitors isolated from a flowering tea, snow Chrysanthemum (the capitula of Coreopsis tinctoria Nutt.)

Methanol extract from the capitula of Coreopsis tinctoria Nutt. (Asteraceae), which is also known as a flowering tea or blooming tea "Snow Chrysanthemum," was found to inhibit the enzymatic activity of aromatase. A total of 24 known isolates (1-24) were identified from the extract, including three chalcones (1-3), an aurone (4), five flavanones (5-9), four flavanols (10-13), a flavonol (14), and two biflavanones (15, 16). Among them, okanin (1, Ki = 1.6 μM), (2S)-naringenin (5, 0.90 μM), isookanin (6, 0.81 μM), (2S)-7,3',5'-trihydroxyflavaone (7, 0.13 μM), and (2S)-5,7,3',5'-tetrahydroxyflavanone (8, 0.32 μM) exhibited relatively potent competitive inhibition. Specifically, the isolates 7 and 8, having a common 3',5'-resorcinol moiety at the B ring in their flavanone skeleton, exhibited potent inhibitory activities compared to those of a clinically applied aminoglutethimide (0.84 μM) and naturally occurring flavone, chrysin (0.23 μM), which is a common non-steroidal aromatase inhibitor. Importantly, the active flavonoid constituents (1 and 5-8) did not inhibit the activity of 5α-reductase enzyme, which normally reacts with the same substrate "testosterone," thus, these compounds were suggested to be specific to aromatase.

Characterization of benzylisoquinoline alkaloid methyltransferases in Liriodendron chinense provides insights into the phylogenic basis of angiosperm alkaloid diversity

Benzylisoquinoline alkaloids (BIAs) are a class of plant secondary metabolites with great pharmacological value. Their biosynthetic pathways have been extensively elucidated in the species from the Ranunculales order, such as poppy and Coptis japonica, in which methylation events play central roles and are directly responsible for BIA chemodiversity. Here, we combined BIA quantitative profiling and transcriptomic analyses to identify novel BIA methyltransferases (MTs) from Liriodendron chinense, a basal angiosperm plant. We identified an N-methyltransferase (LcNMT1) and two O-methyltransferases (LcOMT1 and LcOMT3), and characterized their biochemical functions in vitro. LcNMT1 methylates (S)-coclaurine to produce mono- and dimethylated products. Mutagenesis experiments revealed that a single-residue alteration is sufficient to change its substrate selectivity. LcOMT1 methylates (S)-norcoclaurine at the C6 site and LcOMT3 methylates (S)-coclaurine at the C7 site, respectively. Two key residues of LcOMT3, A115 and T301, are identified as important contributors to its catalytic activity. Compared with Ranunculales-derived NMTs, Magnoliales-derived NMTs were less abundant and had narrower substrate specificity, indicating that NMT expansion has contributed substantially to BIA chemodiversity in angiosperms, particularly in Ranunculales species. In summary, we not only characterized three novel enzymes that could be useful in the biosynthetic production of valuable BIAs but also shed light on the molecular origin of BIAs during angiosperm evolution.

Green Extraction-Assisted Pseudo-Targeted Profile of Alkaloids in Lotus Seed Epicarp Based on UPLC-QTOF MS with IDA

Lotus seed epicarp, a byproduct of lotus, is commonly discarded directly or burned in the cropland, resulting in waste of resources and environmental pollution. In this work, a green ultrasonic-assisted extraction method with ethyl lactate as the extraction solvent was established to extract alkaloids from lotus seed epicarp. The extraction conditions were optimized by response surface methodology. Under the optimal extraction conditions, the extraction of alkaloids from 1 g lotus seed epicarp was accomplished with only 10 mL of extraction solvent within 15 min. Combined with ultrahigh-performance liquid chromatography coupled with quadrupole time-of-flight tandem mass spectrometry with information-dependent acquisition mode, a total of 42 alkaloids were annotated in the lotus seed epicarp extracts. Among them, 39 alkaloids were reported in lotus seed epicarp for the first time. According to quantitative analysis, the distributions and trends of alkaloids in the lotus seed epicarp were found to be similar to those of lotus leaves. The five growth stages of lotus seed epicarp could be successfully distinguished based on the ten representative alkaloids. This study demonstrates that ultrasonic-assisted extraction with ethyl lactate as extractant solvent was efficient in the extraction of alkaloids from lotus seed epicarp, which is a potential renewable resource of bioactive ingredients.

Lotus (Nelumbo nucifera Gaertn.) and Its Bioactive Phytocopounds: A Tribute to Cancer Prevention and Intervention

Simple Summary

The plant Nelumbo nucifera (Gaertn.), commonly known as lotus, sacred lotus, Indian lotus, water lily, or Chinese water lily, is an aquatic perennial crop belonging to the family of Nelumbonaceae. N. nucifera has traditionally been used as an herbal medicine and functional food in many parts of Asia. It has been found that different parts of this plant consist of various bioactive phytocompounds. Within the past few decades, N. nucifera and its phytochemicals have been subjected to intense cancer research. In this review, we critically evaluate the potential of N. nucifera phytoconstituents in cancer prevention and therapy with related mechanisms of action.

Abstract

Cancer is one of the major leading causes of death worldwide. Accumulating evidence suggests a strong relationship between specific dietary habits and cancer development. In recent years, a food-based approach for cancer prevention and intervention has been gaining tremendous attention. Among diverse dietary and medicinal plants, lotus (Nelumbo nucifera Gaertn., family Nymphaeaceae), also known as Indian lotus, sacred lotus or Chinese water lily, has the ability to effectively combat this disease. Various parts of N. nucifera have been utilized as a vegetable as well as an herbal medicine for more than 2000 years in the Asian continent. The rhizome and seeds of N. nucifera represent the main edible parts. Different parts of N. nucifera have been traditionally used to manage different disorders, such as fever, inflammation, insomnia, nervous disorders, epilepsy, hypertension, cardiovascular diseases, obesity, and hyperlipidemia. It is believed that numerous bioactive components, including alkaloids, polyphenols, terpenoids, steroids, and glycosides, are responsible for its various biological and pharmacological activities, such as antioxidant, anti-inflammatory, immune-modulatory, antiviral, hepatoprotective, cardioprotective, and hypoglycemic activities. Nevertheless, there is no comprehensive review with an exclusive focus on the anticancer attributes of diverse phytochemicals from different parts of N. nucifera. In this review, we have analyzed the effects of N. nucifera extracts, fractions and pure compounds on various organ-specific cancer cells and tumor models to understand the cancer-preventive and therapeutic potential and underlying cellular and molecular mechanisms of action of this interesting medicinal and dietary plant. In addition, the bioavailability, pharmacokinetics, and possible toxicity of N. nucifera-derived phytochemicals, as well as current limitations, challenges and future research directions, are also presented.

Alkaloids from lotus (Nelumbo nucifera): recent advances in biosynthesis, pharmacokinetics, bioactivity, safety, and industrial applications

Different parts of lotus (Nelumbo nucifera Gaertn.) including the seeds, rhizomes, leaves, and flowers, are used for medicinal purposes with health promoting and illness preventing benefits. The presence of active chemicals such as alkaloids, phenolic acids, flavonoids, and terpenoids (particularly alkaloids) may account for this plant's pharmacological effects. In this review, we provide a comprehensive overview and summarize up-to-date research on the biosynthesis, pharmacokinetics, and bioactivity of lotus alkaloids as well as their safety. Moreover, the potential uses of lotus alkaloids in the food, pharmaceutical, and cosmetic sectors are explored. Current evidence shows that alkaloids, mainly consisting of aporphines, 1-benzylisoquinolines, and bisbenzylisoquinolines, are present in different parts of lotus. The bioavailability of these alkaloids is relatively low in vivo but can be enhanced by technological modification using nanoliposomes, liposomes, microcapsules, and emulsions. Available data highlights their therapeutic and preventive effects on obesity, diabetes, neurodegeneration, cancer, cardiovascular disease, etc. Additionally, industrial applications of lotus alkaloids include their use as food, medical, and cosmetic ingredients in tea, other beverages, and healthcare products; as lipid-lowering, anticancer, and antipsychotic drugs; and in facial masks, toothpastes, and shower gels. However, their clinical efficacy and safety remains unclear; hence, larger and longer human trials are needed to achieve their safe and effective use with minimal side effects.

Indole Glycosides from Calanthe discolor with Proliferative Activity on Human Hair Follicle Dermal Papilla Cells

A methanol extract from the underground part of Calanthe discolor Lindl. (Orchidaceae) demonstrated significant proliferative activity on human hair follicle dermal papilla cells (HFDPC, % of control: 120.8 ± 0.2%) at 100 µg/mL against HFDPC. Through bioassay-guided separation of the extract, a new indole glycoside named 6'-O-β-D-apiofuranosylindican (1) was isolated along with six known compounds (2-7) including three indole glycosides. The stereostructure of 1 was elucidated based on its spectroscopic properties and chemical characteristics. Among the isolates, 1 (110.0 ± 1.0%), glucoindican (3, 123.9 ± 6.8%), and calanthoside (4, 158.6 ± 7.1%) showed significant proliferative activity at 100 µM. Furthermore, the active indole glycosides (1, 3, and 4) upregulated the expression of vascular endothelial growth factor (VEGF) and fibroblast growth factor-7 (FGF-7) mRNA and protein in HFDPC, which could be the mechanism of their proliferative activity.

Diversity in Chemical Structures and Biological Properties of Plant Alkaloids

Phytochemicals belonging to the group of alkaloids are signature specialized metabolites endowed with countless biological activities. Plants are armored with these naturally produced nitrogenous compounds to combat numerous challenging environmental stress conditions. Traditional and modern healthcare systems have harnessed the potential of these organic compounds for the treatment of many ailments. Various chemical entities (functional groups) attached to the central moiety are responsible for their diverse range of biological properties. The development of the characterization of these plant metabolites and the enzymes involved in their biosynthesis is of an utmost priority to deliver enhanced advantages in terms of biological properties and productivity. Further, the incorporation of whole/partial metabolic pathways in the heterologous system and/or the overexpression of biosynthetic steps in homologous systems have both become alternative and lucrative methods over chemical synthesis in recent times. Moreover, in-depth research on alkaloid biosynthetic pathways has revealed numerous chemical modifications that occur during alkaloidal conversions. These chemical reactions involve glycosylation, acylation, reduction, oxidation, and methylation steps, and they are usually responsible for conferring the biological activities possessed by alkaloids. In this review, we aim to discuss the alkaloidal group of plant specialized metabolites and their brief classification covering major categories. We also emphasize the diversity in the basic structures of plant alkaloids arising through enzymatically catalyzed structural modifications in certain plant species, as well as their emerging diverse biological activities. The role of alkaloids in plant defense and their mechanisms of action are also briefly discussed. Moreover, the commercial utilization of plant alkaloids in the marketplace displaying various applications has been enumerated.

Benzylisoquinoline alkaloids from Nelumbo nucifera Gaertn. petals with antiausterity activities against the HeLa human cervical cancer cell line

Ethanolic extract of Nelumbo nucifera petals showed preferential cytotoxic activity against HeLa human cervical cancer cell line with a PC₅₀ value of 10.4 μg/mL. This active extract was subjected to a phytochemical investigation study which led to the isolation of nine benzylisoquinoline alkaloids (1-9). The isolated compounds exhibited potent antiausterity activities. Moreover, under nutrient-deprived conditions, (-)-lirinidine (8) induced remarkable alterations in HeLa cell morphology including cell shrinkage and plasma blebbing leading to total cell death within 10 h. Mechanistically, 8 was found to inhibit Akt/mTOR signaling pathway. It also induced apoptosis by promoting caspase-3 activation and inhibiting Bcl-2 expression. Therefore, benzylisoquinoline alkaloids skeleton can be considered as a promising scaffold for the anticancer drug development against cervical cancer.

Ent-kaurane-type diterpenoids from Isodonis Herba activate human hair follicle dermal papilla cells proliferation via the Akt/GSK-3β/β-catenin transduction pathway

A methanol extract from Isodonis Herba demonstrated significant proliferative effect on human hair follicle dermal papilla cells (HFDPC, % of control: 150.0 ± 2.0% at 20 µg/mL, p < 0.01). From the extract, 14 ent-kaurane-type diterpenoids (1-14), two abietane-type diterpenoids (15 and 16) and four triterpenoids (17-20) were isolated. Among the isolates, enmein (1, 160.9 ± 3.0% at 20 µM, p < 0.01), isodocarpin (2, 169.3 ± 4.9% at 5 µM, p < 0.01), nodosin (4, 160.5 ± 12.4% at 20 µM, p < 0.01), and oridonin (8, 165.4 ± 10.6% at 10 µM, p < 0.01) showed the proliferative effects. The principal component enmein (1) activated the expression of vascular endothelial growth factor (VEGF) mRNA, upregulated the production of VEGF and increased levels of phospho-Akt, phospho-GSK-3β, and β-catenin accumulation in HFDPC, which could be the mechanism of these activate proliferation activity.

Liquid chromatographic separation of alkaloids in herbal medicines: Current status and perspectives

Alkaloids are a widespread group of basic compounds in herbal medicines and have attracted great interest due to various pharmaceutical activities and desirable druggability. Their distinctive structures make chromatographic separation fairly difficult. Peak tailing, poor resolution, and inferior column-to-column reproducibility are common obstacles to overcome. In order to provide a valuable reference, the methodologies and/or strategies on liquid chromatographic separation of alkaloids in herbal medicines proposed from 2012 to 2019 are thoroughly summarized.

Isolation and characterization of two O-methyltransferases involved in benzylisoquinoline alkaloid biosynthesis in sacred lotus (Nelumbo nucifera)

Benzylisoquinoline alkaloids (BIAs) are a major class of plant metabolites with many pharmacological benefits. Sacred lotus (Nelumbo nucifera) is an ancient aquatic plant of medicinal value because of antiviral and immunomodulatory activities linked to its constituent BIAs. Although more than 30 BIAs belonging to the 1-benzylisoquinoline, aporphine, and bisbenzylisoquinoline structural subclasses and displaying a predominant R-enantiomeric conformation have been isolated from N. nucifera, its BIA biosynthetic genes and enzymes remain unknown. Herein, we report the isolation and biochemical characterization of two O-methyltransferases (OMTs) involved in BIA biosynthesis in sacred lotus. Five homologous genes, designated NnOMT1-5 and encoding polypeptides sharing >40% amino acid sequence identity, were expressed in Escherichia coli Functional characterization of the purified recombinant proteins revealed that NnOMT1 is a regiospecific 1-benzylisoquinoline 6-O-methyltransferase (6OMT) accepting both R- and S-substrates, whereas NnOMT5 is mainly a 7-O-methyltransferase (7OMT), with relatively minor 6OMT activity and a strong stereospecific preference for S-enantiomers. Available aporphines were not accepted as substrates by either enzyme, suggesting that O-methylation precedes BIA formation from 1-benzylisoquinoline intermediates. Km values for NnOMT1 and NnOMT5 were 20 and 13 μm for (R,S)-norcoclaurine and (S)-N-methylcoclaurine, respectively, similar to those for OMTs from other BIA-producing plants. Organ-based correlations of alkaloid content, OMT activity in crude extracts, and OMT gene expression supported physiological roles for NnOMT1 and NnOMT5 in BIA metabolism, occurring primarily in young leaves and embryos of sacred lotus. In summary, our work identifies two OMTs involved in BIA metabolism in the medicinal plant N. nucifera.

BBB-permeable aporphine-type alkaloids in Nelumbo nucifera flowers with accelerative effects on neurite outgrowth in PC-12 cells

Blood-brain barrier (BBB)-permeable components in the methanolic extract of Nelumbo nucifera flowers showed accelerative effects on neurite outgrowth in PC-12 cells. Among the constituents isolated from N. nucifera flowers in our previous study, aporphine-type alkaloids, lirinidine, asimilobine, N-methylasimilobine, and pronuciferine, showed accelerative effects. Lirinidine, N-methylasimilobine, and an alkaloid-rich diethyl ether fraction at low concentrations increased the expression of mRNAs coding for TrkA, Vav3, and Rac1. In addition, good permeability of asimilobine and N-methylasimilobine was confirmed using an in vitro BBB model. Asimilobine and N-methylasimilobine are considered to be suitable as seed compounds of drugs for Alzheimer's disease, because of their activity and BBB permeability.

Quantitative Determination of Principal Aporphine and Benzylisoquinoline Alkaloids Due to Blooming State in Lotus Flower (Flower Buds of Nelumbo nucifera) and Their Hyaluronidase Inhibitory Activity

Using a recently developed analytical protocol, distributions of 5 aporphine alkaloids, nuciferine (1), nornuciferine (2), N-methylasimilobine (3), asimilobine (4), and pronuciferine (5), and 5 benzylisoquinoline alkaloids, armepavine (6), norarmepavine (7), N-methylcoclaurine (8), coclaurine (9), and norjuziphine (10), in lotus flowers (the flower buds of Nelumbo nucifera) were analyzed. The flowers were collected at different blooming states (beginning of blooming, one-third in bloom, half in bloom, three-quarters in bloom, and in full bloom) from Saga prefecture, Japan (NN-S1–5). The samples from the beginning of blooming state (NN-S1, 16.35 mg/g in dried material) were found to possess the richest total alkaloid content (1-10). The samples of half in bloom (NN-S3, 52.69 mg per flower of dried material) had the highest total alkaloid content per flower. Among the alkaloid constituents, nornuciferine (2, IC50 = 22.5 µM), asimilobine (4, 11.7 μM), norarmepavine (7, 26.4 μM), coclaurine (9, 11.4 μM), and norjuziphine (10, 24.3 μM) exhibited hyaluronidase inhibitory activity, which was more potent than that of the antiallergic medicine disodium cromoglycate (DSCG, 64.8 μM).

Benzylisoquinoline Alkaloids Biosynthesis in Sacred Lotus

Sacred lotus (Nelumbo nucifera Gaertn.) is an ancient aquatic plant used throughout Asia for its nutritional and medicinal properties. Benzylisoquinoline alkaloids (BIAs), mostly within the aporphine and bisbenzylisoquinoline structural categories, are among the main bioactive constituents in the plant. The alkaloids of sacred lotus exhibit promising anti-cancer, anti-arrhythmic, anti-HIV, and anti-malarial properties. Despite their pharmacological significance, BIA metabolism in this non-model plant has not been extensively investigated. In this review, we examine the diversity of BIAs in sacred lotus, with an emphasis on the distinctive stereochemistry of alkaloids found in this species. Additionally, we discuss our current understanding of the biosynthetic genes and enzymes involved in the formation of 1-benzylisoquinoline, aporphine, and bisbenzylisoquinoline alkaloids in the plant. We conclude that a comprehensive functional characterization of alkaloid biosynthetic enzymes using both in vitro and in vivo methods is required to advance our limited knowledge of BIA metabolism in the sacred lotus.

Total Synthesis of γ-Alkylidenebutenolides, Potent Melanogenesis Inhibitors from Thai Medicinal Plant Melodorum fruticosum

A hitherto unreported member of γ-alkylidenebutenolides in Melodorum fruticosum (Annonaceae), (4 E)-6-benzoyloxy-7-hydroxy-2,4-heptadiene-4-olide, named as isofruticosinol (4) was isolated from the methanol extract of flowers, along with the known related butenolides, namely, the (4 Z)-isomer (3) of 4, melodrinol (1), and its (4 E)-isomer (2). To unambiguously determine the absolute configuration at the C-6 position in these butenolides, the first total syntheses of both enantiomers of 2-4 were achieved over 6-7 steps from commercially available D- or L-ribose (D- and L-5). Using the same protocol, both enantiomers of 1 were also synthesized. Based on chiral HPLC analysis of all synthetic compounds ( S- and R-1-4), all naturally occurring butenolides were assigned as partial racemic mixtures with respect to the chiral center at C-6 (enantiomeric ratio, 6 S/6 R = ∼83/17). Furthermore, the melanogenesis inhibitory activities of S- and R-1-4 were evaluated, with all shown to be potent inhibitors with IC₅₀ values in the range 0.29-2.9 μM, regardless of differences in the stereochemistry at C-6. In particular, S-4 (IC₅₀ = 0.29 μM) and R-4 (0.39 μM) showed potent inhibitory activities compared with that of reference standard arbutin (174 μM).

Structural Requirements of Alkylglyceryl-l-Ascorbic Acid Derivatives for Melanogenesis Inhibitory Activity

l-Ascorbic acid has multifunctional benefits on skin aesthetics, including inhibition of melanin production, and is widely used in cosmetics. It, however, has low stability and poor skin penetration. We hypothesize that alkylglyceryl-l-ascorbic acid derivatives, highly stable vitamin C–alkylglycerol conjugates, would have similar anti-melanogenic activity with better stability and penetration. We test 28 alkylglyceryl-l-ascorbic acid derivatives (1–28) on theophylline-stimulated B16 melanoma 4A5 cells to determine if they inhibit melanogenesis and establish any structure–function relationships. Although not the most potent inhibitors, 3-O-(2,3-dihydroxypropyl)-2-O-hexyl-l-ascorbic acid (6, IC₅₀ = 81.4 µM) and 2-O-(2,3-dihydroxypropyl)-3-O-hexyl-l-ascorbic acid (20, IC₅₀ = 117 µM) are deemed the best candidate derivatives based on their inhibitory activities and low toxicities. These derivatives are also found to be more stable than l-ascorbic acid and to have favorable characteristics for skin penetration. The following structural requirements for inhibitory activity of alkylglyceryl-l-ascorbic acid derivatives are also determined: (i) alkylation of glyceryl-l-ascorbic acid is essential for inhibitory activity; (ii) the 3-O-alkyl-derivatives (2–14) exhibit stronger inhibitory activity than the corresponding 2-O-alkyl-derivatives (16–28); and (iii) derivatives with longer alkyl chains have stronger inhibitory activities. Mechanistically, our studies suggest that l-ascorbic acid derivatives exert their effects by suppressing the mRNA expression of tyrosinase and tyrosine-related protein-1.

Labdane-Type Diterpenes, Galangalditerpenes A-C, with Melanogenesis Inhibitory Activity from the Fruit of Alpinia galanga

In our continuing study of biologically active natural products from the fruit of Alpinia galanga (Zingiberaceae), we newly isolated three new labdane-type diterpenes, termed galangalditerpenes A–C (1–3), along with four known sesquiterpenes (4–7) and two diterpenes (8 and 9). The stereostructures of 1–3 were elucidated on the basis of their spectroscopic properties. The melanogenesis inhibitory activities in theophylline-stimulated murine B16 melanoma 4A5 cells of these isolates, including the new diterpenes (1–3, IC₅₀ = 4.4, 8.6, and 4.6 μM, respectively), were found to be more than 6–87-fold higher than that of arbutin (174 μM), a commercially available positive control.

Melanogenesis Inhibitory Activity of Diterpenoid and Triterpenoid Constituents from the Aerial Part of Isodon trichocarpus

A methanol extract from the aerial part of Isodon trichocarpus (Labiatae) demonstrated inhibitory effects on melanogenesis in theophylline-stimulated murine B16 melanoma 4A5 cells (IC50 = 1.6 μg/mL). From the extract, nine diterpenoids (1–9) and four triterpenoids (10–13) were isolated. Among the isolates, enmein (1, IC50 = 0.22 μM), isodocarpin (2, 0.19 μM), nodosin (4, 0.46 μM), and oridonin (6, 0.90 μM) showed an inhibitory effect without notable cytotoxicity at the effective concentrations. These diterpenoids (1, 2, 4, and 6) inhibited the expression of tyrosinase, tyrosine-related protein (TRP)-1, and TRP-2 mRNA, which could be the mechanism of melanogenesis inhibitory activity.

Molecular Structure-Affinity Relationship of Flavonoids in Lotus Leaf (Nelumbo nucifera Gaertn.) on Binding to Human Serum Albumin and Bovine Serum Albumin by Spectroscopic Method

Lotus leaf has gained growing popularity as an ingredient in herbal formulations due to its various activities. As main functional components of lotus leaf, the difference in structure of flavonoids affected their binding properties and activities. In this paper, the existence of 11 flavonoids in lotus leaf extract was confirmed by High Performance Liquid Chromatography (HPLC) analysis and 11 flavonoids showed various contents in lotus leaf. The interactions between lotus leaf extract and two kinds of serum albumins (human serum albumin (HSA) and bovine serum albumin (BSA)) were investigated by spectroscopic methods. Based on the fluorescence quenching, the interactions between these flavonoids and serum albumins were further checked in detail. The relationship between the molecular properties of flavonoids and their affinities for serum albumins were analyzed and compared. The hydroxylation on 3 and 3’ position increased the affinities for serum albumins. Moreover, both of the methylation on 3’ position of quercetin and the C₂=C₃ double bond of apigenin and quercetin decreased the affinities for HSA and BSA. The glycosylation lowered the affinities for HSA and BSA depending on the type of sugar moiety. It revealed that the hydrogen bond force played an important role in binding flavonoids to HSA and BSA.

Melanogenesis inhibitory activity of a 7-O-9'-linked neolignan from Alpinia galanga fruit

An aqueous acetone extract from the fruit of Alpinia galanga (Zingiberaceae) demonstrated inhibitory effects on melanogenesis in theophylline-stimulated murine B16 melanoma 4A5 cells (IC₅₀=7.3μg/mL). Through bioassay-guided separation of the extract, a new 7-O-9'-linked neolignan, named galanganol D diacetate (1), was isolated along with 16 known compounds including 14 phenylpropanoids (2-15). The structure of 1, including its absolute stereochemistry in the C-7 position, was elucidated by means of extensive NMR analysis and total synthesis. Among the isolates, 1 (IC₅₀=2.5μM), 1'S-1'-acetoxychavicol acetate (2, 5.0μM), and 1'S-1'-acetoxyeugenol acetate (3, 5.6μM) exhibited a relatively potent inhibitory effect without notable cytotoxicity at effective concentrations. The following structural requirements were suggested to enhance the inhibitory activity of phenylpropanoids on melanogenesis: (i) compounds with 4-acetoxy group exhibit higher activity than those with 4-hydroxy group; (ii) 3-methoxy group dose not affect the activity; (iii) acetylation of the 1'-hydroxy moiety enhances the activity; and (iv) phenylpropanoid dimers with the 7-O-9'-linked neolignan skeleton exhibited higher activity than those with the corresponding monomer. Their respective enantiomers [1' (IC₅₀=1.9μM) and 2' (4.5μM)] and racemic mixtures [(±)-1 (2.2μM) and (±)-2 (4.4μM)] were found to exhibit melanogenesis inhibitory activities equivalent to those of the naturally occurring optical active compounds (1 and 2). Furthermore, the active compounds 1-3 inhibited tyrosinase, tyrosine-related protein (TRP)-1, and TRP-2 mRNA expressions, which could be the mechanism of melanogenesis inhibitory activity.