Synthesis and X-ray Characterization of (E)-4-Methyl-2-(((1-(Prop-2-yn-1-yl)-1H-indol-3 yl)methylene)amino)phenol as a Plant Growth Promoter for Reviving Rootless Narcissus poeticus Bulbs

Abstract

A single crystal of Formula 4, (E)-4-Methyl-2-(((1-(Prop-2-yn-1-yl)-1H-indol-3 yl)methylene)amino)phenol, was efficiently synthesized, with an excellent yield of 96%. The synthetic approach offers an effective and reliable route for synthesized the target compound. Structural elucidation was performed through comprehensive characterization, techniques including single-crystal X-ray diffraction, 1H and 13C NMR spectroscopy, mass spectrometry, and thermogravimetric analysis (TGA) which confirmed molecular identity and crystal packing and hydrogen bonding interactions. Furthermore, the compound exhibits significant plant growth-promoting activity, specifically inducing root formation and rejuvenating rootless or dormant bulbs of Narcissus poeticus, a plant at an optimal concentration of 0.5g / mL of Formula 4. Narcissus poeticus also known for its medicinal value in the treatment of cancer and Parkinson’s disease and it is widely used in the fragrance and perfume industry. These findings suggest that compound 4 could be further explored for its applicability in horticultural and agricultural practices to improve plant establishment and productivity.

Description

Field of InventionThe invention relates to the field of organic chemistry and plant biotechnology, particularly thesynthesis and structural characterization of bioactive indole-based Schiff base with alkynemoiety enhance the action of natural plant hormones like auxins, gibberellins, andbrassinosteroids with overall potential applications as plant growth enhancers. The preparedcompound is well characterized using NMR, mass spectrometry, X-ray crystallographic, andthermogravimetric analysis (TGA). More specifically, it pertains to the development of smallmolecule chemical compounds capable of reviving and stimulating growth in dormant orrootless ornamental plant bulbs, such as Narcissus poeticus, can enhance their productivity,opening avenues for industrial applications in perfumery, medicinal uses, and the synthesis ofvaluable compound. The present invention reports the synthesis, structural characterization,and evaluation of (E)-4-Methyl-2-(((1-(prop-2-yn-1-yl)-1H-indol-3-yl)methylene)amino)phenol as a plant growth promoter.Background of synthesisPlant development and growth are highly controlled by a multi-component interplay ofendogenous hormones namely auxins, gibberellins, and brassinosteroids [1]. Phytohormonesplay a crucial role in numerous physiological processes such as cell division, root hairinitiation, and shoot extension. Nonetheless, environmental stresses, dormancy, or damage tobulbs usually interfere with these native processes [2], resulting in suppressed development oroutright dormancy in some ornamental plants such as Narcissus poeticus. To overcome suchinstances, there is a need for the production of synthetic agents that stimulate development andcan either substitute or supplement native hormones [3].Within the last couple of decades, the development of bioactive small molecules has acquireda strong momentum within both organic chemistry and plant biotechnology. Schiff bases andthose with indole scaffold-based structures [4], in particular, have shown varied biologicalactivities due to their similarity to native biomolecules and ability to bind to receptors of planthormones [5]. The addition of an alkyne moiety adds further enrichment to the bioactivityprofile of these molecules through enhanced molecular rigidity, lipophilicity, and capacity forbiorthogonal conjugation [6], and these combined tend to enhance cell uptake and hormonelike action. This research concerns itself with synthesizing and crystallographic studies a newindole-derived schiff base featuring an alkyne functional group. The compound was efficientlycharacterized by advanced methodologies such as single crystal X-ray diffraction to establishits molecular shape [7] and to ascertain its purity, initial biological assays were conducted,which revealed that the compound exhibits significant plant growth-promoting activity,specifically inducing root formation and rejuvenating rootless or dormant bulbs of Narcissuspoeticus, a plant known for its medicinal value in treating cancer and Parkinson's disease [8].This work lies at the intersection of organic synthesis, structural chemistry, and plant science,offering potential applications in the development of next-generation agrochemicals forornamental horticulture and plant tissue culture systems.References1. Carlos, E.; Lerma, T. A.; Martinez, J. M. Phytohormones and plant growth regulators,a review. J Sci with Technol Appl, 2021, 10, 27-65.2. Yasemin, S.; Beruto, M. A review on flower bulb micropropagation: Challenges andopportunities. Horticulturae, 2024, 10(3), 284.3. Stephany, R. W. Hormonal growth promoting agents in food producinganimals. Springer, 2009, 355-367.4. Sanjurani, T., & Barman, P. The versatile nature of indole containing Schiff bases: Anoverview. Polyhedron, 2024, 249, 116779.5. Kazemi, Z.; Rudbari, H.A.; Moini, N.; Momenbeik, F.; Carnamucio, F.; Micale, N.Indole-containing metal complexes and their medicinal applications. Molecules,2024 29(2), 484.6. Xu, Y.; Huang, D.; Wu, J.; Wu, X. Recent Developments in Selenylation ofAlkynes. Advanced Synthesis & Catalysis, 2024, 366(18), 3761-3789.7. Helliwell, J. R. "Single-crystal X-ray techniques." In International Tables forCrystallography Volume C: Mathematical, physical and chemical tables, Springer,Dordrecht, 2006, 26-41.8. Kornienko, A.; Evidente, A. Chemistry, biology, and medicinal potential ofnarciclasine and its congeners. Chemical reviews, 2008, 108(6), 1982-2014.Objective of the inventionThe main objective of the presented invention is to synthesize a single crystal of (E)-4-Methyl2-(((1-(Prop-2-yn-1-yl)-1H-indol-3yl)methylene)amino)phenol. The compound has beencharacterized using NMR, mass spectrometry, thermogravimetric analysis (TGA) andconfirmed by single-crystal X-ray diffraction and evaluated as a plant growth enabler forreviving rootless Narcissus poeticus bulbs.Summary of the InventionThe invention involves the synthesis, characterization using NMR, mass spectrometry andconfirmed by single-crystal X-ray diffraction of Formula 4 with plant growth-enhancingproperties. It is designed to mimic natural hormones and stimulate regeneration in dormant orrootless Narcissus poeticus bulbs. The chemical structure of synthesized compound ispresented below:Detailed Description of the InventionSchiff base-alkyne hybrids synthesized via condensation reactions have emerged as a versatileclass of compounds with significant biological and material applications. The condensation ofprimary amines with aldehydes or ketones yields Schiff base, which when furtherfunctionalized with alkyne moieties, provide highly tunable scaffolds for subsequentmodifications, including cycloaddition and coordination chemistry. The imine functionality inSchiff bases imparts unique electronic and structural properties, while the alkyne group offersa reactive handle for click-type transformations, enabling the construction of diverse moleculararchitectures. These Schiff base-alkyne conjugates have attracted attention due to their abilityto coordinate with transition metals, generate stable frameworks, and serve as precursors forbioactive heterocycles. Their structural diversity allows for exploration across pharmaceutical,catalytic, and material science domains, where they have shown potential as antimicrobial,plant growth enabler, antioxidant, and sensor agents. The ease of synthesis, functionalversatility, and broad applicability make Schiff base-alkyne systems a rapidly expanding areaof research with promising implications in both medicinal and industrial chemistry.Furthermore, compound 4 significantly promoted root and shoot growth in Narcissus poeticusbulbs, demonstrating its potential as a plant growth-enhancing agent.ExampleMaterials and MethodsStarting materials including 1H-indole-3-carbaldehyde, 2-amino-4-methylphenol, propargylbromide (80% in toluene), and potassium carbonate (K2CO3) were purchased from SigmaAldrich and used without further purification. (E)-4-Methyl-2-(((1-(Prop-2-yn-1-yl)-1H-indol3yl)methylene)amino)phenol was synthesized according to the reported procedure. All of thesolvents used were of analytical grade. The 1 H and 13C NMR spectra were recorded on a Bruker(500 MHz, 125.7 MHz) spectrometer using CDCl3 as an internal reference, and chemical shiftswere reported relative to tetramethylsilane (TMS). Values are given in Hz. Mass spectrumanalysis was conducted on XEVO-G2-XS QTOF mass spectrometer. Melting points weremeasured in a Mel Temp II device using sealed capillaries. Crystal structure visualization wasdone using Mercury 4.0.0.Reference Example (4)Initially compound 2 was prepared by the reaction of 1H-indole-3-carbaldehyde (1 eq) withpropargyl bromide (1.3 eq), K2CO3 (1.5 eq) as base and DMF as solvent. After stirring at roomtemperature for 17h the reaction mixture was poured into ice cold water and the solidprecipitates were obtained as the final product. The prepared compounds 2 (1-(prop-2-yn-1-yl)-1H-indole-3-carbaldehyde) (1eq) and 2-amino-4-methylphenol (1eq) were added to a100mL RBF and dissolved in Methanol solvent. Dark green coloured of solution was observedreaction mixture was refluxed at 80-90⁰C for 17h. After that green colour crystal of desiredcompound 4 was filter out.Dark green coloured crystals product (Formula 13), Yield: 98 %, M.P.: 140-146 ⁰C,IR (Neatcm-1): 956 (C-C), 1162, 1249 (N-CH2), 1288 (CH2=N),1458, 1620 (C=N), 2978 (CH2C≡H)1H NMR (500 MHz, CDCl3) δH 8.57 (s, 2H, CHN, CHN'), 8.43 (s, 2H, H1, H1'), 7.54 (s, 2H,-Tz-H, -Tz-H,), 7.26-7.17 (m, 8H, H3, H3',H4, H4',H5, H5',H6, H6'), 7.12 (d, J = 5.2 Hz, 4H,H8, H9, H10, H11), 5.41 (s, 4HCH2, CH2'), 4.19 (t, J = 7.1 Hz, 4H, N3CH2CH2, N3CH2CH2,'),3.66 (q, J = 7.0 Hz, 12H, OCH2CH3), 1.94-1.82 (m, 4H, CCH2C), 1.10 (t, J = 7.0 Hz,18H,OCH2CH3) 0.42 (t, J = 7.8 Hz, 2H,) 13C NMR (125.7 MHz, CDCl3) δ 155.7, 142.1, 140.2,136.7, 131.5, 128.5, 124.6, 123.6, 123.3, 121.7, 121.1, 117.3, 111.1, 56.1, 51.4, 45.7, 23.5,18.5, 7.2. ESI- mass: m / z calculated for [M]+279.11; found 279.09.Scheme 1. Synthesis of Formula 4Method of Crystal GrowthThe single crystals of Formula 4 was obtained by the slow evaporation of solvent method. Auniform solution of the forementioned compound was prepared by dissolving it in CH3OH:mixture solvent, covered with aluminium foil with pin holes and kept undisturbed. After 7 daysshiny green crystals were observed which was directly characterized by single crystal X-rayDiffractometer.X-ray crystallographic analysis of compound 4The structural elucidation by Single crystal XRD analysis confirms that the formula 4crystallizes in triclinic crystal system with 4 molecules of compound within a unit cell withP1 space group. The Cambridge Crystallographic Data Centre (CCDC) no. of compound is2392398. The crystal data and experimental details for respective compounds are shown inTable 1 and ORTEP diagrams in Fig 4. Resolved 3D crystal structure of the compound 4. Fig5. (a-d) shows an asymmetrical unit of compound 4, unit cell packing of compound 4 along aaxis, H-bonding between the molecules and (d) lattice arrangement of compound 4 along baxis.Table 1. Crystal data and experimental details of compound 4Bioassay studiesThe Fig 8. and Fig 9. illustrates the comparative growth response of Narcissus poeticus bulbstreated with different concentrations of Compound 4 over 30 to 60 days respectively. Whilethe untreated control bulbs displayed minimal root and shoot growth, treatment withCompound 4 resulted in marked improvements in both root length and shoot elongation. Theeffect was concentration-dependent, with progressive growth observed up to 0.5 mg / L, whichproved to be the most effective dose for stimulating vigorous root proliferation and shootdevelopment. However, beyond this concentration, a significant decline in growth was noted,indicating that 0.5 mg / L represents the optimal level of Compound 4 for enhancing plantgrowth. However, beyond this concentration, a significant decline in growth was noted,indicating that 0.5 mg / L represents the optimal level of Compound 4 for enhancing plantgrowth.Table 2. Effect of compound 4 on Narcissus poeticus after 60 daysThe experimental results indicate that treatment with compound 4 significantly enhanced both root andshoot (leaf) growth compared to the control. Table 2 indicate in the untreated bulbs, leaf growth wasminimal (no leaf in bulb 1 and 3 cm in bulb 2), and root lengths were very short (3-4.5 cm). However,upon treatment, both parameters improved markedly. At 0.05--0.45 mg / L, leaf lengths reached up to22 cm, while root lengths extended up to 39 cm. Further enhancement was observed at higherconcentrations, with maximum leaf length of 27 cm and root length of 47 cm at 0.45 mg / L. The numberof roots also increased, peaking at 8 primary roots under 0.45 mg / L treatment. These findings clearlysuggest that compound 4 positively influences both root system development and shoot elongation,with the effect being concentration-dependent.ConclusionA compound 4 has been formed via condensation approach with high percentage yield andpurity. The prepared compound is characterized using NMR, Mass spectrometry and X-raycrystallography. The bioassay study demonstrated that compound 4 exerts a significantstimulatory effect on the growth of Narcissus poeticus bulbs by enhancing both root and shootdevelopment. The treatment exhibited a clear growth-promoting potential compared tountreated controls, indicating its role as a bioactive agent in plant growth regulation. Thesefindings suggest that compound 4 could be further explored for its applicability in horticulturaland agricultural practices to improve plant establishment and productivity.

Claims

1. A single crystal of compound; (E)-4-Methyl-2-(((1-(Prop-2-yn-1-yl)-1H-indol-3 yl)methylene)amino)phenol of Formula 4 bearing the following structure and molecular formula C19H16N2O is prepared which exhibits significant chemical and structural stability as characterized by standard spectroscopic and analytical techniques.

2. For preparing the compound 4, method as claimed in claim 1, comprises of synthesizing a terminal alkyne-functionalized indole (2) derivative and tertiary amine (3) subsequently subjecting these synthesized molecules to undergo condensation reaction in the presence of an organic solvent ethanol at 65°C for 17h to yield the target compound 4.

3. X-ray diffraction structure of single crystal of the Formula 4 as claimed in Claim 1, for detailed atomic arrangement of the molecule.

4. The Formula 4 as claimed in claim 1 compound; (E)-4-Methyl-2-(((1-(Prop-2-yn-1-yl)- 1H-indol-3 yl)methylene)amino)phenol bearing the following structure is a plant growth promoter for reviving rootless Narcissus poeticus bulbs at best concentration (0.5 mg / L) from dormant bulb to green plantlet.