Totarol

Discovery

Totarol was discovered in 1910 by New Zealand scientist Sir Thomas Hill Easterfield. While investigating the properties of Miro, Kahikatea, Rimu, Matai and Totara, Easterfield detected a "crystalline bloom" on totara boards a few hours after leaving the planing machine. After extraction of totarol from Podocarpus totara, Easterfield observed no other compound had been cited in chemical literature before with this formula. Easterfield and his colleague J.C McDowell proposed the name "totarol" in a follow-up paper in 1915, as the crystalline substance was believed to possess a tertiary alcohol group. In 1937 Short and Stromberg continued investigations, publishing Totarol Part 1. In 1951 Short and Wang became the first to identify the chemical structure of totarol with their paper Totarol Part 2.

Occurrence

Although totarol was first isolated in Podocarpus totara, totarol has also been identified in numerous other species of Podocarpaceae and Cupressaceae, with the majority found in the genus Podocarpus of the family Podocarpaceae and the subfamily Cupressoideae of the family Cupressaceae. Outside Podocarpus and Cupressoideae, totarol is rarely found in the plant kingdom. However, totarol has recently been isolated in Rosmarinus officinalis (rosemary). The gymnosperms that contain totarol are distributed worldwide but are concentrated in North America, the far-south regions of South America, East Asia and East Africa.

Biological activity

Antimicrobial activity

Totarol motivates research in drug discovery due to its ability to inhibit numerous microorganisms. Totarol exhibits antimicrobial properties in numerous species including gram-positive bacteria, acid-fast bacteria, nematodes, parasitic protozoans, crustaceous foulers (Table 1). In addition to inhibiting microorganisms by itself, totarol exhibits inhibitory synergy with currently used antimicrobial drugs: totarol potentiates isonicotinic acid hydrazide against various Mycobacteria.; methicillin against Mycobacterium tuberculosis and Staphylococcus aureus; and anacardic acid and erythromycin against Staphylococcus aureus. In nature, totarol is a key player in gymnosperm's defense against harmful microbes: gymnosperms that produce totarol are resistant to rotting.

Table 1. Antibacterial activity of totarol against microorganisms

Mechanism of antimicrobial inhibition

Although totarol exhibits antimicrobial properties, the mode of action is unclear and various methods of inhibitory action have been proposed. In Staphylococcus aureus strains resistant to penicillin via creation of penicillin binding protein 2' (PBP2'), totarol may inhibit the synthesis of PBP2'. but this is very unlikely because totarol is also effective against anaerobic organisms. Recently totarol was also hypothesized to inhibit gram-positive and acid-fast bacteria via inhibition of FtsZ protein, which forms the Z-ring, a polymer necessary for efficient bacterial cell cytokinesis.

Totarol may also function by disrupting the structural integrity of the phospholipid bilayer of bacteria by weakening Van der Waals interactions with its phenolic group, which also results in bacterial cells unable to synthesize ATP. Motivation for totarol functioning via disruption of membrane structure is due to its high phospholipid/water partition coefficient. However, totarol's partitioning capability was only observed at concentrations 10 to 100 fold higher than required for antibacterial activity. Thus it is unlikely that totarol is an uncoupler of bacterial respiration at the low levels observed in antimicrobial studies.

Traditional use

The use of Podocarpus totara extract in Māori medicines for treatment of fevers, asthma, coughs, cholera, distemper, chest complaints and venereal disease dates back to over 100 years. The timber of Podocarpus totara is renowned for its resilience against rotting, which made it valuable to Māori for housing, waka (canoes), fencing, pā stockades, drinking vessels, shovels and carvings in chiefs houses. Tōtara bark was used to cover kelp bags containing preserved muttonbirds known as pōhā. The tōtara tree was accorded divine status by Māori based on its immense size and its use in making waka employed on long, dangerous voyages. Carved tōtara can be viewed as a representation of ancestry and historical and mythological events. The tōtara can also be seen to represent a connection between the past and the present, the secular and the spiritual. It has a strong link to Māori creation stories as it reaches down to Papatūānuku (Mother Earth) and up towards Ranginui (Sky Father). The roots in the symbolism of the tōtara mark out a genealogical reference point which Māori believe ties them to the natural world, the whenua (land) and their ancestral rohe (territory). In Māori tradition tōtara is the first born child of Tāne-Mahuta and the forest goddess Mumuwhango and is considered a noble tree. According to tradition, felling a tōtara wasn't possible without seeking permission from Tāne-Mahuta. This involved performing specific rituals and chanting karakia (invocation). European settlers of New Zealand used the wood for wharf piles, bridges, railway sleepers, telegraph poles, lighthouses, mining equipment, fence posts and foundation blocks. The durability stems from the anti-bacterial activity of totarol. Houses, churches, grave markers, and even cobbles and kerbs were made of tōtara; strips of the bark were used as a roofing material. The presence of totarol means tōtara wood resists decay and insect attack in the heart timber.

Totarol has been found in organic matter in the embankments of a Neolithic site in Northern Sweden. Scientists have suggested that totarol from Cupressaceae resin at the site was used for its antibacterial and antifungal properties to preserve meat, as well as for its ability to repel insects. Totarol has been observed in the endemic Mexican plant Buddleja perfoliata, used in traditional medicine as a topical antiseptic and diuretic against headaches, colds, tuberculosis, heart disease, dizziness and nervousness. Totarol has also been identified in the leaves of Algerian grown ethnomedicinal shrub Myrtus Communis. Leaf extract from the flowering plant has been used historically as a medicine known as "El Rayhan". It was used as a decoction, infusion and health remedy for bathing newborns with inflamed skin and washing sores. Additionally, it was used to treat oral wounds, disorders of the digestive and urinary systems, diarrhea, peptic ulcers, hemorrhoids and inflammations. Totarol was detected in a 2024 Myrtus Communis leaf extract study and described as having considerable anti-inflammatory potential. Totarol from juniper or cypress trees was used in ancient Egyptian mummification. In 2023 totarol was found in an embalming workshop dated to around 664-525BC a few meters south of the pyramid of King Unas at Saqqara. Despite totarol's demonstrated antimicrobial efficacy, its commercial application remains primarily confined to the cosmetic industry. For totarol to be considered for clinical use, a comprehensive understanding of its mode of action is essential.

Biochemical properties

Totarol decreases the plasma levels of estrogens and can also effectively reduce pathogenic hepatic cells in vitro. Totarol's anti-cancer activity is hypothesized to be due to the natural product's ability to form an o-quinone methide in vivo. Totarol also prevents cells from undergoing oxidative stress in vitro by acting as a hydrogen donor to peroxy radicals or reacting with other peroxy radicals to terminate undesirable radical reactions.

Biosynthesis

Totarol is a precursor to the formation of nagilactones that possess antifungal properties not possessed by totarol. Consequently, gymnosperms that produce totarol and nagilactones are able to defend themselves against bacteria and fungi.

The biosynthesis of totarol was difficult to determine. The main reason for the challenge in determining how the secondary metabolite is produced is because totarol does not follow the isoprene rule: the isopropyl group of totarol is in the "wrong" place This hypothesis was motivated by the well known santonin-desmotroposantonin rearrangement of steroid dienones into aromatic compounds. It is now accepted that totarol is synthesized biologically from ferruginol. Geranyl geranyl pyrophosphate 4 undergoes typical diterpene cyclization to form (−)-abietadiene 5, which is oxidized to form ferruginol 3, which proceeds through a spiro intermediate to form totarol (Scheme 2).

Synthesis

Totarol has been the subject of numerous syntheses. The first total synthesis of totarol (Scheme 3) utilized 6 and the alkyne 7 to yield 8 which was converted to the corresponding ketone 9 via hydrogenation followed by cyclization with polyphosphoric acid. 9 was subsequently converted to 10 and another ketone that were inseparable by chromatography. The synthesis was finalized by treatment with N-Bromosuccinimide followed by debromination to yield (±)-totarol. The main downfall of this synthesis was that in multiple steps, complete conversion of reactant to products was not observed and undesirable side products were often not separable by chromatography. However, since this was the first total synthesis of (±)-totarol, it is notable.

Total enantioselective synthesis

The first total enantioselective synthesis of totarol was achieved in 1979 (Scheme 4). The key step in the synthesis is the formation of 13 via a Wittig reaction between 11 and 12. This same cyclization can also be achieved via a Friedel-Crafts alkylation and cyclization. Subsequent hydrogenation of 13 followed by intramolecular cyclization with aluminium chloride forms the B ring and totarylmethyl ether which is demethylated by boron tribromide to yield totarol.

A more recent organic synthesis of totarol was achieved by utilizing 14, a lamdane diterpene named zamoranic acid (Scheme 5). The addition of the isopropyl group in the chemical synthesis was achieved with complete stereoselectivity. Acetylation to yield 15 required high temperatures due to the steric hindrance of the isopropyl group. Cis-hydroxylation followed by cleavage with H5IO6 yielded a diol that was acylated in pyridine and oxidized to give 16. The key step in the synthesis was the cyclization of ring C: 16 was treated with SmI2 to yield totarane diastereomers which were separated by column chromatography. The desired diastereomer was treated with p-TsOH in benzene to yield 17. The synthesis was completed by a halogenation-dehydrogenation sequence and subsequent bromination to yield 18 and ring aromatization with elimination via a lithium complex.

Total chemoenzymatic synthesis

Chemoenzymatic synthesis of totarol has also been achieved with high yield (41.8%) (Scheme 6). A racemic beta-keto ester 19 undergoes lipase-assisted resolution to yield chiral alcohol 20. Treatment of 20 with 10% HCl and p-TsOH gives αβ-unsaturated ketone 21. A Michael addition with the anion obtained from the reaction of methyl 5-methyl-3-oxohexanoate 13 with NaOMe gives a 2:1 diastereomeric mixture of 22 which is hydrolyzed to yield 23 which is brominated and debrominated to yield totarol.

Research

Extraction

Totarol is extracted by supercritical extraction. The process uses high pressure carbon dioxide under specific temperature, pressure and gas flow conditions to extract totarol from powdered tōtara wood. Totarol can be extracted from dead wood, negating the need to cut down live trees. Although totarol can be extracted from other Podocarpus, some trees in the cypress family (cypress, juniper, thuja) and from rosemary, it is most abundant in Podocarpus totara.

Products

Products for sale containing totarol include toothpastes, tooth tablets, mouthwash, toners, cleansers, moisturisers, face masks, concealers, blemish control, anti-acne, pimple patches, face cream, eye cream, sun screen, deodorants, face mists, facial wash, anti-wrinkle, restorative serum, renew cream, scar removal serum, dandruff control, scalp treatment, shampoo bar, pet skin cream, pet shampoo, pet deodorant, pet healing clay, pet skin therapy shampoo/ spray, pet paw wash, healing balm, hand wash, hand cream, pressed powder makeup, mascara, rescue cream, skin whitener, lip tint, pregnancy body oil, mouth freshener, sore throat relief, cold and flu nasal spray.

Other uses

Totarol may also be used as an indicator for the quality of juniper berry based spirits. Juniper berries that contain diterpenoids including totarol are used for the aromatization and production of some gins. Consequently, totarol can aid in the characterization of different types of gin or commercial brands, vouching for the authenticity and quality of the product.

Totarol has been found on the posterior tibia of Frieseomelitta silvestrii languida, a species of stingless bees from Brazil. Frieseomelitta silvestrii languida collect resin to create a protective barrier around the opening of their nest to ward off insects from settling near the nest's entrance. The presence of totarol can aid in the determination of this bee species.

References

References

1. "(4bS)-trans-8,8-Trimethyl-4b,5,6,7,8,8a,9,10-octahydro-1-isopropylphenanthren-2-ol". [[Sigma-Aldrich]].
2. (1937). "116. Totarol. Part I.". Journal of the Chemical Society (Resumed).
3. (1995). "Totarol: a Non-Conventional Diterpenoid". Australian Journal of Chemistry.
4. (1910). "Studies on the chemistry of the New Zealand flora. Part IV.—The chemistry of the Podocarpi.". Transactions and Proceedings of the New Zealand Institute.
5. (1915). "The chemistry of ''Podocarpus totara'' and ''Podocarpus spicatus''.". Transactions of the New Zealand Institute.
6. (1951). "662. Totarol. Part II". Journal of the Chemical Society (Resumed).
7. (February 2001). "Totarol, totaradiol and ferruginol: three diterpenes from Thuja plicata (Cupressaceae)". Biochemical Systematics and Ecology.
8. (June 2008). "An unprecedented condensation pathway leading to the formation of phenolic C40 bis-diterpenoids in sediments from the Lower Oligocene of the Rhine Rift Valley.". Organic Geochemistry.
9. (1995). "Totarol: A non-conventional diterpenoid.". Australian Journal of Chemistry.
10. (2001). "World Checklist and Bibliography of Conifers". Royal Botanic Gardens.
11. (November 2004). "Antimycobacterial constituents from Juniperus procera, Ferula communis and Plumbago zeylanica and their in vitro synergistic activity with isonicotinic acid hydrazide". Phytotherapy Research.
12. (January 2005). "Plants as a source of bacterial resistance modulators and anti-infective agents.". Phytochemistry Reviews.
13. (October 1992). "Antibacterial activity of totarol and its potentiation". Journal of Natural Products.
14. (December 2007). "The phenolic diterpene totarol inhibits multidrug efflux pump activity in Staphylococcus aureus". Antimicrobial Agents and Chemotherapy.
15. (December 2008). "Antiparasitic, nematicidal and antifouling constituents from Juniperus berries". Phytotherapy Research.
16. (September 1999). "The synthesis and antibacterial activity of totarol derivatives. Part 1: modifications of ring-C and pro-drugs". Bioorganic & Medicinal Chemistry.
17. (December 2009). "Antimycobacterial terpenoids from Juniperus communis L. (Cuppressaceae)". Journal of Ethnopharmacology.
18. (April 1996). "Antibacterial activity of anacardic acid and totarol, alone and in combination with methicillin, against methicillin-resistant Staphylococcus aureus". The Journal of Applied Bacteriology.
19. (June 1996). "Inhibition of lipid peroxidation by diterpenoid from Podocarpus nagi". Experientia.
20. (August 1998). "Inhibition of oral bacteria by phenolic compounds. Part 1. QSAR analysis using molecular connectivity.". Quantitative Structure-Activity Relationships.
21. (April 2007). "Totarol inhibits bacterial cytokinesis by perturbing the assembly dynamics of FtsZ". Biochemistry.
22. (April 2001). "Effects of (+)-totarol, a diterpenoid antibacterial agent, on phospholipid model membranes". Biochimica et Biophysica Acta (BBA) - Biomembranes.
23. (December 2000). "A fluorescence study of the interaction and location of (+)-totarol, a diterpenoid bioactive molecule, in model membranes". Biochimica et Biophysica Acta (BBA) - Biomembranes.
24. (October 2002). "A MAS-NMR study of the location of (+)-totarol, a diterpenoid bioactive molecule, in phospholipid model membranes". Chemistry and Physics of Lipids.
25. (July 2000). "The synthesis and antibacterial activity of totarol derivatives. Part 3: Modification of ring-B". Bioorganic & Medicinal Chemistry.
26. (January 2010). "Ethnobotany, phytochemistry and pharmacology of Podocarpus sensu latissimo (sl).". South African Journal of Botany.
27. "Pōhā, airtight storage containers. Science Learning Hub, Pokapū Akoranga Pūtaiao".
28. "Pōhā Tītī - Te Papa New Zealand".
29. (July 1, 2020). "Podocarpus Totara".
30. Simpson, Philip. "Totara: A Natural and Cultural History". University of Auckland Press.
31. (2021). "Ko te Rākau Hei Tohu Mō te Rangahau Me te Tuhi Whakapapa: Tree Symbolism as a Method for Researching and Writing Genealogy". Genealogy.
32. Neich, Roger. (2001). "Carved Histories: Rotorua Ngati Tarawhai Woodcarving". Auckland University Press.
33. Irwin, James. (1984). "An Introduction to Māori Religion". Bedford Park - Australian Association for the Study of Religions.
34. Gilchrist, Shane. (July 24, 2017). "Children of Tane".
35. Duncan, C R. (2004-01-01). "Fire protection of New Zealand's traditional Maori buildings".
36. Cuevas-Cianca SI, Leal AC, Hernández LR, Arreola ES, Bach H. (October 13, 2022). "Antimicrobial, toxicity, and anti-inflammatory activities of Buddleja perfoliata Kunth". Phytomedicine Plus.
37. Belahcene, Samia. (February 14, 2024). "Chemical Composition Antioxidant and Anti-Inflammatory Activities of Myrtus communis L. Leaf Extract: Forecasting ADMET Profiling and Anti-Inflammatory Targets Using Molecular Docking Tools". Molecules.
38. Maxime Rageot, Ramadan B. Hussein, Susanne Beck, Victoria Altmann-Wendling, Mohammed I. M. Ibrahim, Mahmoud M. Bahgat, Ahmed M. Yousef, Katja Mittelstaedt, Jean-Jacques Filippi, Stephen Buckley, Cynthianne Spiteri & Philipp W. Stockhammer. (February 1, 2023). "Biomolecular analyses enable new insights into ancient Egyptian embalming".
39. (August 2002). "Aromatase inhibitory activities of standishinal and the diterpenoids from the bark of Thuja standishii". Planta Medica.
40. (July 2008). "Antifibrotic activity of diterpenes from Biota orientalis leaves on hepatic stellate cells". Archives of Pharmacal Research.
41. (July 2002). "o-Quinone methides: intermediates underdeveloped and underutilized in organic synthesis.". Tetrahedron.
42. Bailly, Christian. (2020-12-01). "Anticancer Activities and Mechanism of Action of Nagilactones, a Group of Terpenoid Lactones Isolated from Podocarpus Species". Natural Products and Bioprospecting.
43. (December 1993). "Antibacterial activity of long-chain alcohols against Streptococcus mutans.". Journal of Agricultural and Food Chemistry.
44. (1951). "662. Totarol. Part II". Journal of the Chemical Society (Resumed).
45. (1958). "520. Experiments on the synthesis of diterpenes. Part I. A total synthesis of (±)-totarol". Journal of the Chemical Society (Resumed).
46. (May 1979). "The Total Synthesis of (+)-Totarol and (+)-Podototarin.". Bulletin of the Chemical Society of Japan.
47. (January 1992). "Stereocontrolled total synthesis of (±)-totaryl methyl ether and (±)-semperviryl methyl ether.". Tetrahedron.
48. (December 2003). "Synthesis of (+)-totarol.". Tetrahedron Letters.
49. (December 2007). "Chemoenzymatic synthesis of (+)-totarol,(+)-podototarin,(+)-sempervirol, and (+)-jolkinolides E and D.". Tetrahedron: Asymmetry.
50. RC Cambie, SG Brooker, MA James. (May 18, 1966). "A New Zealand Phytochemical Register—Part II. Transactions of the Royal Society of New Zealand: General, Volume 1, Issue 20, 18 May 1966, Page 205".
51. CR Bennett, RC Cambie. (21 February 1966). "Chemistry of the podocarpaceae—XI: Reductions of totarol". Tetrahedron.
52. (October 1992). "Antibacterial activity of totarol and its potentiation". Journal of Natural Products.
53. (April 1996). "Antibacterial activity of anacardic acid and totarol, alone and in combination with methicillin, against methicillin-resistant Staphylococcus aureus". The Journal of Applied Bacteriology.
54. (1997-06-01). "Antioxidative Action of Diterpenoids from Podocarpus nagi". Planta Medica.
55. Nicolson, Kirsty. (1998). "Antibacterial properties of diterpenes and their derivatives: a thesis presented in partial fulfilment of the requirements for the degree of Master of Science in Microbiology at Massey University". Massey University.
56. (September 1999). "The synthesis and antibacterial activity of totarol derivatives. Part 1: modifications of ring-C and pro-drugs". Bioorganic & Medicinal Chemistry.
57. (1999-10-01). "Potentiation of methicillin activity against methicillin-resistant Staphylococcus aureus by diterpenes". FEMS Microbiology Letters.
58. (October 2000). "A Mosquito Larvicidal Diterpenoid Isolated from Podocarpus totara D. Don ex Lambert". Journal of Entomological Science.
59. (December 2009). "Antimycobacterial terpenoids from Juniperus communis L. (Cuppressaceae)". Journal of Ethnopharmacology.
60. (April 2001). "Effects of (+)-totarol, a diterpenoid antibacterial agent, on phospholipid model membranes". Biochimica et Biophysica Acta (BBA) - Biomembranes.
61. (February 2002). "The propolis of stingless bees: terpenes from the tibia of three Frieseomelitta species". Journal of Insect Physiology.
62. (October 2003). "Synthesis of totarol amino alcohol derivatives and their antiplasmodial activity and cytotoxicity". Bioorganic & Medicinal Chemistry.
63. (2004). ["Chemical modification and pharmacological evaluation of the antimalarial natural product totarol ). University of Cape Town.
64. "Method for treating skin disorders".
65. (August 15, 2006). "The use of totarol to treat acne in an adolescent: A case study". NZFP.
66. (2007-12-05). "The Antifungal Compound Totarol of Thujopsis dolabrata var. hondai Seeds Selects for Fungi on Seedling Root Surfaces". Journal of Chemical Ecology.
67. (December 2007). "The phenolic diterpene totarol inhibits multidrug efflux pump activity in Staphylococcus aureus". Antimicrobial Agents and Chemotherapy.
68. (April 2007). "Totarol inhibits bacterial cytokinesis by perturbing the assembly dynamics of FtsZ". Biochemistry.
69. (December 2015). "Totarol prevents neuronal injury in vitro and ameliorates brain ischemic stroke: Potential roles of Akt activation and HO-1 induction". Toxicology and Applied Pharmacology.
70. (January 2015). "A comprehensive proteomic analysis of totarol induced alterations in Bacillus subtilis by multipronged quantitative proteomics". Journal of Proteomics.
71. (October 2017). "Effects of Ultrasound Treatment on Physiochemical Properties and Antimicrobial Activities of Whey Protein-Totarol Nanoparticles". Journal of Food Protection.
72. (September 2017). "Preventing Surgical Site Infections Using a Natural, Biodegradable, Antibacterial Coating on Surgical Sutures". Molecules.
73. (October 2018). "A Metabolomic and HPLC-MS/MS Analysis of the Foliar Phenolics, Flavonoids and Coumarins of the ''Fraxinus'' Species Resistant and Susceptible to Emerald Ash Borer". Molecules.
74. (March 2018). "Antibacterial activity and mode of action of totarol against ''Staphylococcus aureus'' in carrot juice". Journal of Food Science and Technology.
75. "Fire, meat and totarol: organic matter in the embankments of the Neolithic site Bastuloken (North Sweden)". Analytical Pyrolysis Letters.
76. (September 25, 2019). "The application of natural antibacterial coating for the surface modification of dental implants and abutments". Clinical Oral Implants Research.
77. (2020-04-24). "Formulation and Functional Properties of Whey Protein-Based Tissue Adhesive Using Totarol as an Antimicrobial Agent". Processes.
78. (March 2020). "Minimum Inhibitory and Bactericidal Concentrations of a Totarol™ formulation against Staphylococcus aureus strains obtained from bovine intramammary infections in New Zealand".
79. Zeqian Xu, Stefanie Krajewski, Tobias Weindl, Ronny Loeffler, Ping Li, Xingting Han, Jürgen Geis-Gerstorfer, Hans-Peter Wendel, Lutz Scheideler, Frank Rupp. (January 28, 2020). "Application of totarol as natural antibacterial coating on dental implants for prevention of peri-implantitis".
80. (October 2021). "Design, Hemisynthesis, crystal structure and anticancer activity of 1, 2, 3-triazoles derivatives of totarol". Bioorganic Chemistry.
81. Bell A, Jones B, Bridges J, Ward-McGrath H. (December 2021). "Some observations on the treatment of superficial pyoderma in dogs with totarol".
82. (2022-06-21). "PLGA-Based Nanoplatforms in Drug Delivery for Inhibition and Destruction of Microbial Biofilm". Frontiers in Cellular and Infection Microbiology.
83. (October 13, 2022). "Antimicrobial, toxicity, and anti-inflammatory activities of Buddleja perfoliata Kunth". Phytomedicine Plus.
84. (November 3, 2022). "Larvicidal potential of Thuja orientalis leaves and fruits extracts against Culex pipiens (Diptera: Culicidae)". Journal of King Saud University - Science.
85. (December 8, 2022). "Computational modelling of some phenolic diterpenoid compounds as anti-influenza A virus agents". Scientific African.
86. (July 11, 2023). "Design and synthesis of novel totarol derivatives bearing carbamate moiety as potential fungicides". Monatshefte für Chemie - Chemical Monthly.
87. (22 February 2024). "A balance of biocompatibility and antibacterial capability of 3D printed PEEK implants with natural totarol coating". Dental Materials.
88. (2024). "Efficacy of totarol against Staphylococcus pseudintermedius and Staphylococcus coagulans in dogs and cats: An in vitro study". Japanese Journal of Veterinary Research.
89. (2024). "1,2,3-Triazole-totarol conjugates as potent PIP5K1α lipid kinase inhibitors". Bioorganic & Medicinal Chemistry.
90. (July 29, 2024). "Totarol exhibits antibacterial effects through antibiofilm and combined interaction against vancomycin-resistant Enterococcus faecalis". Canadian Journal of Microbiology.
91. Hoisang, Jitpean, Seesupa, Kamlangchai, Makpunpol, Ngowwatana, Chaimongkol, Khunbutsri, Khlongkhlaeo, Kampa. (2024). "Evaluation of Totarol for Promoting Open Wound Healing in Dogs". Veterinary Sciences.
92. (July 23, 2023). "Bioactive Totarol".
93. "Products with Totarol". INCIDecoder.
94. (November 2008). "Assessment of some diterpenoids in commercial distilled gin". Analytica Chimica Acta.
95. (February 2002). "The propolis of stingless bees: terpenes from the tibia of three Frieseomelitta species". Journal of Insect Physiology.