Pyranocoumarin Scaffolds and Stereochemistry: Fusion Modes, Saturation States, Conformations, and Hydroxy-Group Esterification of the Six-Membered Oxygen-Containing Ring
Pyranocoumarin Scaffolds and Stereochemistry: Fusion Modes, Saturation States, Conformations, and Hydroxy-Group Esterification of the Six-Membered Oxygen-Containing Ring
Introduction
Pyranocoumarins are a class of compounds formed by the fusion of a six-membered oxygen-containing heterocycle to a coumarin scaffold. The fusion position of the six-membered oxygen-containing ring, the degree of saturation of the carbon–carbon double bond within the ring, and the substituents on the ring collectively affect the electronic structure and three-dimensional conformation of the molecule. Natural pyranocoumarins include both unsaturated structures that retain an intracyclic carbon–carbon double bond and dihydropyranocoumarins. In a dihydropyran structure, the proportion of sp³ carbons increases and the planar constraint of the ring is consequently reduced; when an sp³ carbon in the ring is bonded to four different substituents, a stereogenic center can form, giving rise to enantiomers or diastereomers.[1]
The structural differences between pyranocoumarins and furanocoumarins also involve the aromaticity, degree of saturation, and conformational freedom of the fused heterocycle. The fused furan ring in furanocoumarins is aromatic and forms a relatively continuous π-conjugated system with the coumarin core, imposing a strong planar constraint on the overall structure. By contrast, the six-membered oxygen-containing ring of pyranocoumarins can have different saturation states; as the number of sp³ carbons increases, nonplanar ring folding and conformational variation become more pronounced. In the dihydropyran ring of khellactone and its esterified derivatives, C3′ and C4′ are adjacent oxygenated sp³ carbons and can form two adjacent stereogenic centers. The molecular properties are therefore further influenced by ring conformation, hydrogen bonding, hydrophobic interactions, and stereochemical configuration.[1,4]
1 Fusion Modes and Scaffold Types of the Six-Membered Oxygen-Containing Ring
1.1 Formation of the Six-Membered Oxygen-Containing Ring
During pyranocoumarin biosynthesis, a hydroxycoumarin first undergoes ortho-prenylation. The resulting intermediate then undergoes intramolecular oxidative cyclization, in which the oxygen atom of the phenolic hydroxyl group forms a C–O bond with the adjacent prenyl side chain, thereby producing a six-membered oxygen-containing heterocycle that shares two adjacent carbon atoms with the benzene ring of the coumarin.[1] Part of the original flexible side chain is incorporated into the fused ring, reducing rotational freedom and consequently altering the overall molecular shape and local electronic structure.
The structural change can be represented as follows:
Side-chain cyclization → formation of a six-membered oxygen-containing ring → restricted intramolecular rotation → fixation of the intracyclic double bond and substituents at specific spatial positions.
Whether the six-membered oxygen-containing ring retains a carbon–carbon double bond further affects the hybridization states of its local carbon atoms. The intracyclic alkene carbons in unsaturated pyranocoumarins remain sp²-hybridized. In dihydropyranocoumarins, the corresponding carbon atoms become sp³-hybridized, which weakens the planar constraint of the ring and increases the possibility of nonplanar conformations and stereogenic-center formation.
1.2 Linear, Angular, and Other Fusion Modes
Natural pyranocoumarins can be classified as linear, angular, or other less common fused forms according to the position at which the six-membered oxygen-containing ring is fused to the coumarin core. Ring-forming regions reported in the literature include the 4,5-, 5,6-, 6,7-, and 7,8-positions, with many representative natural products arising from fusion at the 6,7- and 7,8-positions.[1]
Scaffold type | Fusion characteristics of the six-membered ring | Representative compounds | Main structural features |
Linear pyranocoumarins | The six-membered ring produces a relatively extended tricyclic outline | Xanthyletin and decursinol | Include unsaturated parent scaffolds and dihydro derivatives containing a single stereogenic center |
Angular pyranocoumarins | The six-membered ring forms a bent tricyclic outline with the coumarin | Seselin, khellactone, and praeruptorins | Include both unsaturated structures and khellactone-type dihydro derivatives; the latter often contain adjacent stereogenic centers and ester groups |
Complex fused pyran systems | Contain additional oxygen-containing rings or further fused structures | Calanolide A and related compounds | The numbers of rings and stereogenic centers are further increased |
Linear and angular forms differ in their ring-fusion topology. Hydroxy, methoxy, acyl, and hydrocarbon-chain substituents occur on the corresponding scaffolds and further alter the electronic structure and intermolecular interactions.
1.3 Xanthyletin and Seselin as Ring-Fusion Positional Isomers
Xanthyletin and seselin are both unsaturated pyranocoumarins with the molecular formula C₁₄H₁₂O₃. They differ in the fusion position and topological orientation of the newly formed pyran ring relative to the coumarin core and therefore form linear and angular scaffolds, respectively.
Changing the ring-fusion position reorients the six-membered ring relative to the long axis of the coumarin and also alters the molecular shape, local dipole direction, and accessible surface. Seselin is a typical angular pyranocoumarin. Its single-crystal structure shows that the coumarin moiety is nearly planar, whereas the six-membered oxygen-containing ring adopts a distorted half-chair conformation.[2]
2 Saturation of the Six-Membered Ring and π-Electronic Structure
2.1 Local Conjugation in an Unsaturated Pyran Ring
The six-membered oxygen-containing ring of an unsaturated pyranocoumarin retains a carbon–carbon double bond. The two sp² carbons of the double bond possess mutually parallel p orbitals that can undergo π-orbital coupling with the adjacent aromatic system.
The local electronic structure can be represented as follows:
Presence of an intracyclic C=C bond → retention of p orbitals on the sp² carbons → electronic coupling with the adjacent benzene ring → a relatively strong local planar constraint on the ring.
The six-membered oxygen-containing ring is not itself equivalent to a fully aromatic ring. The extent of its conjugation is jointly determined by the position of the double bond, the ring oxygen atom, the fusion mode, and the structure of the parent scaffold.
2.2 Hydrogenation of the Double Bond and the sp²→sp³ Transition
After hydrogenation of the carbon–carbon double bond in the pyran ring, the corresponding carbon atoms change from sp² to sp³ hybridization:
C=C → C–C → interruption of continuous p-orbital overlap at this position → formation of tetrahedral carbons → weakening of the planar constraint on the ring.
The near-tetrahedral bond angles of sp³ carbons give the six-membered ring greater freedom to fold. The benzene ring and α-pyrone structure of the coumarin itself remain conjugated; local saturation primarily changes the conformation of the newly formed six-membered ring and its conformational relationship with the coumarin core.
2.3 Dihydropyran Structures and the Formation of Stereogenic Centers
Decursinol is a linear dihydropyranocoumarin. After partial saturation of the six-membered oxygen-containing ring, the hydroxy-bearing sp³ carbon is bonded to four different substituents and consequently becomes a stereogenic center.
This structural change gives rise to the following sequence:
Saturation of the intracyclic C=C bond and formation of a hydroxy-bearing sp³ carbon
→ conversion of trigonal-planar geometry into tetrahedral geometry
→ bonding of the hydroxy-bearing carbon to four different groups, making it a stereogenic center
→ formation of a pair of enantiomers.
(+)-Decursinol and its enantiomer of the opposite configuration have the same elemental composition and two-dimensional connectivity but differ in the three-dimensional orientation of their substituents. This enantiomeric relationship makes most of their conventional physical properties very similar in achiral environments, whereas their interactions in chiral environments can differ.
3 Six-Membered-Ring Conformation and Three-Dimensional Molecular Structure
3.1 Distorted Half-Chair Conformation of Seselin
Single-crystal X-ray diffraction of seselin shows that the coumarin moiety is nearly planar, whereas the fused α-pyran ring adopts a distorted half-chair conformation. Intermolecular C–H···O interactions are also present.[2]
The three-dimensional structure of the six-membered ring is jointly governed by the intracyclic double bond and the sp³ carbons. The double bond restricts the relative rotation of some atoms, whereas the remaining ring atoms can still deviate from the mean plane. Bulky substituents such as gem-dimethyl groups can also alter intracyclic bond angles and dihedral angles.
3.2 Conformational Changes in Tetrahydroseselin
Tetrahydroseselin is an angular pyranocoumarin obtained by catalytic hydrogenation of seselin. Relative to seselin, this product contains four additional hydrogen atoms: the carbon–carbon double bonds in both the newly formed pyran ring and the α,β-unsaturated lactone ring of the coumarin are reduced. Its crystal structure therefore reflects the conformational changes accompanying hydrogenation of both double bonds and cannot be regarded as a single-variable comparison involving only the saturation of the newly formed pyran ring.[3]
Single-crystal X-ray structure of tetrahydroseselin. Displacement ellipsoids are drawn at the 50% probability level, and O1, O2, and O3 denote oxygen atoms. The crystal structure shows that both outer six-membered oxygen-containing rings adopt distorted half-chair conformations. C2, C3, C7, and C8 deviate by approximately 0.282, 0.446, 0.241, and 0.687 Å, respectively, from the planes defined by the other four nearly coplanar atoms in their corresponding rings. Tetrahydroseselin is formed by hydrogenation of seselin. Conversion of the intracyclic carbon–carbon double bonds into single bonds changes the corresponding carbon atoms from sp² to sp³ hybridization, reduces local π-orbital continuity, and increases the conformational freedom of the rings. In this crystal structure, both outer six-membered oxygen-containing rings display nonplanar half-chair conformations.[3]
Figure source: Bauri A K, Foro S, Rahman A F M M. Acta Crystallographica Section E: Crystallographic Communications, 2017, Figure 1. The original article is distributed under a Creative Commons Attribution license (CC BY).
3.3 Ring Substituents and Conformational Energy
Hydroxy, acyloxy, and gem-dimethyl groups alter the energy differences among the various conformations of a six-membered ring. Larger substituents increase steric repulsion, while rotatable acyl groups increase the number of local conformations. Carbonyl and hydroxy groups can stabilize specific spatial arrangements through dipolar interactions and hydrogen bonding.
Partial saturation of the six-membered ring provides the sp³ geometry required for conformational folding, while ring substituents further modulate the relative stability of individual conformations. The three-dimensional shapes of khellactone and its diester derivatives are jointly controlled by ring conformation and the spatial orientations of the substituents.
4 The Khellactone Scaffold and C3′/C4′ Stereochemistry
4.1 Adjacent Oxygenated Stereogenic Centers
Khellactone is an important core scaffold of angular dihydropyranocoumarins. C3′ and C4′ in its six-membered oxygen-containing ring are adjacent oxygenated sp³ carbons, and both positions can form stereogenic centers. Chirality at C3′ and C4′ is common among angular pyranocoumarins derived from Peucedani Radix, giving rise to multiple sets of enantiomers and diastereomers.[4]
The local structural change can be represented as follows:
Unsaturated C3′/C4′ structure
→ conversion of both positions into oxygenated sp³ carbons
→ generation of two tetrahedral stereogenic centers
→ multiple combinations of the spatial orientations of the two substituents.
Complete structural assignment requires determination of both relative and absolute configurations.
4.2 cis/trans Relative Configuration and R/S Absolute Configuration
The terms cis and trans describe the relative spatial orientations of the two substituents at C3′ and C4′ on the ring, whereas R/S descriptors specify the absolute configuration of each stereogenic center according to the Cahn–Ingold–Prelog sequence rules.
Khellactones containing two stereogenic centers can form different stereochemical combinations. A pair of nonsuperimposable mirror-image structures are enantiomers; structures in which only one stereogenic center is inverted, or that have another non-mirror-image relationship, are diastereomers.
A positive or negative sign of optical rotation denotes the experimentally measured direction of optical rotation and has no fixed one-to-one correspondence with R/S configuration. The complete names of khellactone compounds must specify the relevant stereogenic centers and their configurations.
4.3 Acylation of Khellactone Hydroxy Groups and Praeruptorins
The C3′ and C4′ hydroxy groups of khellactone can form different carboxylic acid esters. Important structural differences among natural praeruptorins arise from the acyl-group identity, attachment position, and C3′/C4′ configuration.[4–7]
Compound | Major structural changes at C3′/C4′ | Structural features |
Khellactone | Hydroxy groups are retained at both positions | Contains two hydrogen-bond donors and two adjacent stereogenic centers |
Praeruptorin A | The C3′ and C4′ hydroxy groups form different esters | Free hydroxy groups are lost, and acetyl/alkenoyl side chains are introduced |
Praeruptorin B | Both the C3′ and C4′ hydroxy groups form relatively bulky unsaturated carboxylic acid esters | The contributions of nonpolar surface area and flexible side chains are further increased |
Praeruptorin C | The C3′ and C4′ hydroxy groups form a diester with different acyl-group compositions | Hydrocarbon-chain branching and saturation are altered |
Qianhucoumarin I | Combination of 2-methylbutanoyl and acetyl groups | A saturated branched chain and a small acyl group coexist |
Qianhucoumarin II | Combination of acetyl and angeloyl groups | The unsaturated acyl group changes the side-chain geometry |
Qianhucoumarin III | Combination of a C3′ acetoxy group and a C4′ tigloyloxy group | Double-bond geometry further affects side-chain orientation |
Pteryxin | Khellactone diester structure | Acyl-group position and composition create an independent structural type |
Takata et al. identified qianhucoumarins I, II, and III as 3′(S)-2-methylbutanoyloxy-4′(R)-acetoxy-3′,4′-dihydroseselin, 3′(S)-acetoxy-4′(R)-angeloyloxy-3′,4′-dihydroseselin, and 3′(S)-acetoxy-4′(R)-tigloyloxy-3′,4′-dihydroseselin, respectively.[7]
When different acyl groups are attached to the two adjacent stereogenic centers of the same angular dihydropyran core, multiple levels of structural variation can arise, including attachment-position isomerism, side-chain geometric isomerism, and stereoisomerism.
5 Hydroxy-Group Acylation and Intermolecular Interactions
5.1 Redistribution of Hydrogen-Bond Donors and Acceptors
Acylation of khellactone hydroxy groups involves the following functional-group transformation:
C–OH → C–O–C(=O)–R
When a free hydroxy group is converted into an ester, the original O–H hydrogen-bond donor is lost, while the newly introduced ester carbonyl acts as a hydrogen-bond acceptor. The hydrocarbon chain of the acyl group also increases the nonpolar surface area, and its rotatable single bonds increase local conformational freedom.
The changes in properties following acylation comprise three independent but simultaneous processes:
① The number of hydrogen-bond donors decreases;
② The contributions of carbonyl acceptors and dipoles increase;
③ Nonpolar carbon chains and flexible structural elements increase.
The overall polarity and hydrophobicity of the molecule are jointly determined by these factors, crystal packing, and molecular conformation.
5.2 Acyl-Group Size, Branching, and Double Bonds
An acetyl group contains one short methyl group; angeloyl and tigloyl groups contain branched unsaturated carbon chains; and 2-methylbutanoyl and isovaleryl groups possess relatively flexible saturated branched chains. Different acyl groups simultaneously alter hydrocarbon-chain volume, degree of branching, double-bond geometry, and the number of rotatable bonds.
Changes in acyl-group structure produce the following differences in properties:
Acyl-group structural variable | Change in molecular structure | Principal physicochemical effect |
Hydrocarbon-chain elongation | Increased nonpolar surface area | Increased contribution from hydrophobic interactions |
Increased branching | Increased local steric volume | Altered conformation and modes of molecular approach |
Introduction of a C=C bond | Increased sp² character and restricted local rotation | More conformationally constrained side-chain geometry |
Conversion of an OH group into an ester | Loss of a hydrogen-bond donor and addition of a carbonyl acceptor | Altered hydration and intermolecular hydrogen-bonding patterns |
Interchange of acyl-group positions | Redistribution of dipoles and steric volume | Possible changes in the NMR chemical environment and chromatographic retention |
5.3 Adjacent Hydroxy Groups and Acyl Migration
In khellactone monoesters, the adjacent hydroxy and ester groups are located on the same dihydropyran ring. In specific cis configurations, the two oxygenated sites are spatially close enough for intramolecular acyl migration to occur. Hong and Kim observed acyl migration in cis-monoacyl khellactones during their investigation of the absolute configurations of khellactone esters.[5]
Acyl migration changes the attachment position between C3′ and C4′ without changing the identity of the acyl group present in the molecule. Structural identification must distinguish between two separate questions: “Which acyl group is present?” and “To which stereogenic center is the acyl group attached?”
6 Stereochemical Structure and Spectroscopic and Chromatographic Properties
6.1 NMR Reflects Relative Configuration and Substitution Position
Nuclear magnetic resonance (NMR) spectroscopy can provide the chemical shifts, coupling constants, and spatial-proximity information of the vicinal protons at C3′ and C4′.
The coupling constant between C3′–H and C4′–H is influenced by the H–C–C–H dihedral angle, while the nuclear Overhauser effect can reveal the spatial proximity of adjacent protons or substituents. In their structural characterization of angular khellactone diesters, Lee et al. combined one- and two-dimensional NMR spectroscopy with high-resolution mass spectrometry to identify the dihydropyran ring, the two oxygenated methine groups, and the attachment positions of the different acyl groups.[6]
The conformation of the six-membered ring also affects the coupling constants. Assignment of relative configuration requires the combined consideration of vicinal coupling, spatial correlations, and the conformation of the entire ring.
6.2 Enantiomers Require Chirality-Sensitive Information
A pair of enantiomers has identical atomic connectivity and molecular formulas, and their conventional NMR, infrared, and mass spectra are highly similar in achiral media. A chiral environment allows the two mirror-image structures to engage in different interactions.
Methods used to determine the absolute configurations of angular pyranocoumarins include single-crystal X-ray diffraction, Mosher chiral derivatization, electronic circular dichroism, and chiral chromatography.[4,5] Song et al. hydrolyzed the pyranocoumarins under investigation to a common cis-khellactone and then compared it with known (+) and (−) enantiomers by chiral chromatography, thereby determining the absolute configurations of the original compounds.[4]
6.3 Diastereomers Have Different Achiral Physicochemical Environments
Diastereomers are not mirror images of each other. Inversion of some stereogenic centers can alter molecular conformation, dipole orientation, distances between substituents, and intramolecular interactions.
These changes can directly affect:
① NMR chemical shifts;
② Vicinal proton coupling constants;
③ Intramolecular hydrogen bonding;
④ Retention on achiral chromatographic stationary phases;
⑤ Crystal packing and solid-state properties such as melting point.
Structural identification of a pyranocoumarin comprises four levels: molecular formula, atomic connectivity, relative configuration, and absolute configuration.
7 Relationships Between Structural Variables and Physicochemical Properties
Structural variable | Change in electronic structure or intermolecular interactions | Physicochemical or analytical properties | Representative compounds |
Formation of a fused six-membered oxygen-containing ring on coumarin | A flexible side chain becomes a ring structure, restricting molecular motion | Altered rigidity and overall molecular shape | Xanthyletin and seselin |
Change in the fusion position of the six-membered ring | Altered tricyclic topology and spatial shape | Changes in molecular packing, dipole orientation, and molecular contact surface | Xanthyletin and seselin |
Retention of an intracyclic C=C bond | Retention of local sp² character and π-orbital coupling | Relatively strong local planar constraint | Seselin |
Hydrogenation of a C=C bond | Conversion of sp² carbons to sp³ carbons and reduced local p-orbital continuity | Increased folding freedom of the six-membered ring | Tetrahydroseselin |
Bonding of an sp³ carbon to four different groups | Formation of a single stereogenic center | Enantiomerism arises | (+)/(−)-Decursinol |
Formation of adjacent stereogenic centers at C3′ and C4′ | Multiple combinations of three-dimensional substituent orientations | Enantiomers and diastereomers arise | Khellactone |
Presence of two free OH groups | Provision of hydrogen-bond donors and acceptors | Hydration, crystal hydrogen bonding, and conformation are affected | Khellactone |
Esterification of OH groups | Fewer hydrogen-bond donors and more ester carbonyl groups and hydrocarbon chains | Altered hydrogen-bonding patterns, hydrophobic interactions, and conformational freedom | Praeruptorins A and B |
Change in acyl-group identity | Altered hydrocarbon-chain length, branching, and double-bond state | Changes in partitioning and chromatographic retention | Praeruptorins A, B, and C |
Change in C3′/C4′ substitution positions | Redistribution of dipoles and steric volume | Altered NMR and chromatographic behavior | Qianhucoumarins I, II, and III |
Simultaneous inversion of two stereogenic centers to form enantiomers | Identical atomic connectivity, with inversion of all relevant stereogenic centers | Properties are highly similar in achiral environments; chirality-sensitive analysis is required for differentiation | cis-Khellactone enantiomers |
Formation of multiple fused oxygen-containing rings | Increased numbers of rings and stereogenic centers and greater rigidity | Increased conformational and stereochemical complexity | Calanolide A |
These structural changes represent general trends. Actual solubility, partition coefficients, chromatographic retention, crystal properties, and biological activity are also influenced by the complete substitution pattern, absolute configuration, conformation, solvent or stationary phase, and crystal form. Their directions cannot be predicted with certainty solely from linear/angular classification, the proportion of sp³ carbons, or a change in a single acyl group.
8 Classification and Research Applications of Representative Pyranocoumarin Products According to Scaffold, Saturation, and Stereochemistry
Table 1. Linear Unsaturated Pyranocoumarins
Classification | CAS No. | Aladdin Cat. No. | Name | Specification or purity | Product features and applications |
Parent-scaffold type without additional oxygenated substituents | 553-19-5 | Xanthyletin | ≥95% | Retains a linearly fused unsaturated six-membered oxygen-containing ring and can serve as a structural reference for this parent scaffold. It is suitable for studies of the intracyclic C=C bond, local conjugation, and structural rigidity, as well as structure–property comparisons with methoxy- and hydroxy-substituted compounds. | |
Methoxy-substituted type | 84-99-1 | Xanthoxyletin | ≥98% | Contains a methoxy group on the xanthyletin-type linear unsaturated scaffold. It can be compared with luvangetin as a pair of methoxy positional isomers to investigate the effects of substitution position on the electronic environment of the aromatic region, NMR chemical shifts, and chromatographic retention. | |
Methoxy-substituted type | 483-92-1 | Luvangetin | ≥98% | Contains a linear unsaturated pyranocoumarin scaffold and a methoxy group. It can be paired with xanthoxyletin as a positional-isomer reference for studies of methoxy attachment position, local electron distribution, and separation behavior. | |
Hydroxy-substituted type | 165900-08-3 | 3′-Hydroxyxanthyletin | — | Introduces a free hydroxy group onto the unsaturated pyranocoumarin scaffold. It can be used to compare hydrogen-bond-donor capacity, polarity, intermolecular interactions, and chromatographic retention before and after hydroxy-group introduction and provides a direct structural comparison with xanthyletin. |
Table 2. Linear Dihydropyranocoumarins and Their Monoesters
Classification | CAS No. | Aladdin Cat. No. | Name | Specification or purity | Product features and applications |
Monohydroxy type (single enantiomer) | 23458-02-8 | Decursinol | Moligand™, ≥99% | Partial saturation of the six-membered oxygen-containing ring produces a hydroxy-bearing stereogenic center. The compound can be used to investigate the sp²-to-sp³ carbon transition, dihydropyran-ring conformation, and a single stereogenic center and can be compared with the racemate in studies of chiral chromatographic separation and enantiomeric purity. | |
Monohydroxy type (racemate) | 5993-18-0 | (±)-Decursinol | ≥98% | Has the same two-dimensional connectivity as a single decursinol enantiomer but contains a pair of enantiomers. It can be used in chiral chromatographic method development, enantiomer recognition, and comparisons of analytical responses between a single enantiomer and the racemate. | |
3-Methylbut-2-enoyl monoester type | 5928-25-6 | Decursin | ≥98% | The decursinol hydroxy group forms an ester with a branched unsaturated carboxylic acid. It can be used to investigate the effects of hydroxy-group esterification—including loss of a hydrogen-bond donor, addition of an ester carbonyl, and introduction of an unsaturated hydrophobic side chain—on conformation and chromatographic retention. | |
Angeloyl monoester type | 130848-06-5 | Decursinol Angelate | ≥98% | An angelic acid ester of decursinol. Comparison with decursin permits investigation of how the structure and double-bond substitution pattern of an unsaturated five-carbon acyl group on the same dihydropyran core affect side-chain geometry, molecular conformation, and chromatographic behavior. |
Table 3. Angular Dihydropyranocoumarins: Khellactone and Its Diester Derivatives
Classification | CAS No. | Aladdin Cat. No. | Name | Specification or purity | Product features and applications |
Vicinal-dihydroxy parent-scaffold type | 518-76-3 | Khellactone | ≥98% | C3′ and C4′ are adjacent hydroxy-substituted sp³ carbons. The compound can serve as the nonesterified parent-scaffold reference for khellactone esters and can be used to compare six-membered-ring conformation and structural and physicochemical properties before and after hydroxy-group esterification. | |
C3′-Acetoxy/C4′-angeloyloxy diester type | 13161-75-6 | Pteryxin | ≥98% | Can be used to assign the C3′/C4′ esterification positions. Together with praeruptorin A, it provides a structural comparison in which the attachment positions of the two ester groups are interchanged and is suitable for investigating ester attachment positions by NMR and differences in chromatographic retention. | |
C3′-Angeloyloxy/C4′-acetoxy diester type (racemate) | 73069-25-7 | Praeruptorin A | ≥98% | A khellactone diester containing angeloyl and acetyl groups. It can be used to investigate C3′/C4′ acyl positional isomerism and, together with a single-enantiomer product, to study enantiomer separation and chiral analysis. | |
C3′-Angeloyloxy/C4′-acetoxy diester type (single enantiomer) | 73069-27-9 | (+)-Praeruptorin A | — | Has a defined single stereochemical configuration and can serve as a chiral reference for the corresponding praeruptorin A type. It is suitable for chiral chromatography, enantiomeric-purity and absolute-configuration studies, and stereochemical comparison of compounds with the same two-dimensional connectivity. | |
C3′,C4′-Bis(angeloyloxy) diester type | 81740-07-0 | Praeruptorin B | ≥98% | The C3′ and C4′ hydroxy groups both form unsaturated angelic acid esters. It can be used to investigate the effects of two angeloyloxy groups on side-chain geometry, nonpolar surface area, and conformation and, by comparison with praeruptorin A, the property changes that occur when the C4′ acetate is replaced by an angelate. | |
C3′-Angeloyloxy/C4′-isovaleryloxy diester type | 72463-77-5 | Praeruptorin C | ≥98% | Contains both an unsaturated angeloyl group and a saturated isovaleryl group. It can be used to compare how the saturation state, side-chain flexibility, and hydrophobic interactions of five-carbon acyl groups affect the conformation and chromatographic retention of khellactone diesters. | |
C3′-[3-Methylbut-2-enoyloxy]/C4′-acetoxy diester type | 477-33-8 | Samidin | ≥95% (LC/MS-ELSD) | Contains 3-methylbut-2-enoyl and acetyl groups. Comparison with the angeloyl/acetyl combination permits investigation of how the branching position and double-bond substitution pattern of an unsaturated five-carbon acyl group affect three-dimensional structure, NMR signals, and chromatographic separation. | |
C3′-[2-Methylbutanoyloxy]/C4′-acetoxy diester type | 477-32-7 | Visnadine | ≥95% (LC/MS-ELSD) | Contains a saturated 2-methylbutanoyl group and an additional side-chain stereochemical element. It can be used to investigate stereostructure when stereogenic centers in the parent scaffold and a chiral acyl group coexist, as well as differences in conformation and chromatographic behavior relative to unsaturated acyl analogues. | |
C3′-Acetoxy/C4′-isovaleryloxy diester type | 53023-17-9 | Suksdorfin | — | Contains acetyl and saturated isovaleryl groups. It can be used to investigate the C3′/C4′ distribution of acyl groups, conformational freedom and hydrophobic interactions following introduction of a saturated branched chain, and differences between the branched-chain structures of isovaleryl and 2-methylbutanoyl groups by comparison with visnadine. |
Note: The products listed above are representative Aladdin products relevant to scientific research. Specific uses should be determined in conjunction with the product specifications, batch COA, and the target reaction or evaluation system. Additional information on product specifications, grades, and COAs can be retrieved from the Aladdin website using the product name, CAS number, or catalog number.
References
[1] Khandy M T, Sofronova A K, Gorpenchenko T Y, Chirikova N K. Plant Pyranocoumarins: Description, Biosynthesis, Application. Plants, 2022, 11(22): 3135. DOI: 10.3390/plants11223135.
[2] Bauri A K, Foro S, Lindner H J, Nayak S K. Reinvestigation of Seselin. Acta Crystallographica Section E, 2006, 62: o1340–o1341. DOI: 10.1107/S1600536806008221.
[3] Bauri A K, Foro S, Rahman A F M M. Crystal Structure of Tetrahydroseselin, an Angular Pyranocoumarin. Acta Crystallographica Section E: Crystallographic Communications, 2017, 73: 1117–1120. DOI: 10.1107/S205698901700932X.
[4] Song Y L, Zhang Q W, Li Y P, Yan R, Wang Y T. Enantioseparation and Absolute Configuration Determination of Angular-Type Pyranocoumarins from Peucedani Radix Using Enzymatic Hydrolysis and Chiral HPLC-MS/MS Analysis. Molecules, 2012, 17(4): 4236–4251. DOI: 10.3390/molecules17044236.
[5] Hong M J, Kim J. Determination of the Absolute Configuration of Khellactone Esters from Peucedanum japonicum Roots. Journal of Natural Products, 2017, 80(5): 1354–1360. DOI: 10.1021/acs.jnatprod.6b00947.
[6] Lee J, Lee Y J, Kim J, Bang O S. Pyranocoumarins from Root Extracts of Peucedanum praeruptorum Dunn with Multidrug Resistance Reversal and Anti-Inflammatory Activities. Molecules, 2015, 20(12): 20967–20978. DOI: 10.3390/molecules201219738.
[7] Takata M, Shibata S, Okuyama T. Structures of Angular Pyranocoumarins of Bai-Hua Qian-Hu, the Root of Peucedanum praeruptorum. Planta Medica, 1990, 56(3): 307–311. DOI: 10.1055/s-2006-960966.
[8] National Center for Biotechnology Information. PubChem Compound Database. Xanthyletin, Xanthoxyletin, Luvangetin, Decursinol, Khellactone, Praeruptorin A and related pyranocoumarins.
For more related articles, see below:
Will glycosylation affect the biological activity of recombinant protein?
危险品化学品经营许可证（带存储）