BIODIVERSITAS ISSN: 1412-033X Volume 23, Number 4, April 2022 E-ISSN: 2085-4722 Pages: 2225-2230 DOI: 10.13057/biodiv/d230458 The potency of selected ethnomedicinal plants from East Kalimantan, Indonesia as antidiabetic agents and free-radical scavengers RICO RAMADHAN 1,2,♥ , PREECHA PHUWAPRAISIRISAN 3 , RUDIANTO AMIRTA 4 , MUHAMMAD FADIL BAGAS DARMAWAN 1 , KAUTSAR UL-HAQ 1,2 , IRAWAN WIJAYA KUSUMA 4 , HERY SUWITO 1,2 , NURLITA ABDULGANI 5 , AHMAD MUKHDLOR 6 , SAPARWADI 7 1 Department of Chemistry, Faculty of Science and Technology, Universitas Airlangga. Jl. Mulyorejo, Surabaya 60115, East Java, Indonesia. Tel./fax.: +62-31-5936501,  email: rico.ramadhan@fst.unair.ac.id 2 Division of Exploration and Synthesis of Bioactive Compounds, University CoE-Research Center for Bio-Molecule Engineering, Universitas Airlangga. Jl. Mulyorejo, Surabaya 60115, East Java, Indonesia 3 Center of Excellent in Natural Products, Department of Chemistry, Faculty of Sciences, Chulalongkorn University. 254 Phayathai Road, Pathumwan, Bangkok 10330, Thailand 4 Laboratory of Forest Products Chemistry and Renewable Energy, Faculty of Forestry, Universitas Mulawarman. Jl. Penajam, Gunung Kelua, Samarinda 75123, East Kalimantan, Indonesia 5 Department of Biology, Faculty of Sciences and Data Analytics, Institut Teknologi Sepuluh November. Jl. Raya ITS, Keputih, Sukolilo, Surabaya 60117, East Java, Indonesia 6 Department of Forest Products Technology, Faculty of Forestry, Universitas Gadjah Mada. Jl. Agro, Bulaksumur, Sleman 55281, Yogyakarta, Indonesia 7 Yayasan Biosfer Manusia (BIOMA). Jl. A. Wahab Syahranie, Sempaja, Samarinda 75119, East Kalimantan, Indonesia Manuscript received: 1 March 2022. Revision accepted: 29 March 2022. Abstract. Ramadhan R, Phuwapraisirisan P, Amirta R, Darmawan MFB, Ul-Haq K, Kusuma IW, Suwito H, Abdulgani N, Mukhdlor A, Saparwadi. 2022. The potency of selected ethnomedicinal plants from East Kalimantan, Indonesia as antidiabetic agents and free- radical scavengers. Biodiversitas 23: 2225-2230. Ten ethnomedicinal plant extracts from East Kalimantan flora, traditionally used to treat blood sugar levels and other diabetes-related diseases, were examined in vitro for their antidiabetic and free radical scavenging activities by inhibiting rat alpha-glucosidase and several free radicals such as DPPH, ABTS, and Nitric oxide respectively. Out of the ten plant species investigated for their antidiabetic activity against maltase and sucrase rat alpha-glucosidase, three exhibited the strongest α- glucosidase inhibitory activity with maltose as a substrate, namely extracts of Garcinia nervosa, Syzygium caudatilimbum, and Shorea balangeran with IC50 values of 0.046; 0.037; 0.045 mg/mL. Meanwhile, quercetin as a positive control appeared to have a comparable IC50 value. Furthermore, among the ten extracts, Syzygium caudatilimbum, Shorea balangeran, and Ixora javanica showed good inhibition against sucrase rat alpha-glucosidase. Moreover, the antioxidant test showed that the ten methanol extracts of plants from East Kalimantan have an antioxidant activity indicated by IC50 values. The present study confirms that the ethnopharmacological use of selected plants from East Kalimantan might have potential as an antidiabetic and natural antioxidant. Keywords: Antidiabetic, antioxidant, biodiversity, ethnomedicinal plants, free radicals INTRODUCTION Historically, medicinal plants have been the main source of treasure in tropical countries. Medicinal plants, a non-timber forest product (NTFP), are a significant constituent of livelihood (Salhi et al. 2019). Human cultures have utilized plants not only for staple food but also for therapy against diseases dan illnesses (Shaw et al. 2010). The use of medicinal plants for disease prevention and treatment has been well established globally for more than a few decades (Mudau et al. 2022). In East Kalimantan, ethnomedicinal plants are the most accessible form of health care resource, particularly to local people living far from the capital city. The local people of East Kalimantan (Dayak tribes) pass down significant information on potential plants in the forest for traditional ceremonies and medicines from generation to generation (Joshi et al. 2004). This traditional knowledge can be considered as scientific evidence practiced by local people who actually apply medicinal plants as particular remedies. Medicinal plants contain many secondary metabolites (phytochemicals), such as polyphenols, coumarins, alkaloids, triterpenes, and other metabolites, that exhibit biological activities including antibacterial, antifungal, anti- inflammatory, antioxidant, antidiabetes, and antiplasmodial (Maroyi 2017; Onyango et al. 2019) that may create their therapeutic properties. Type-2 diabetes mellitus (T2DM) is one of the most chronic diseases characterized by hyperglycemia. Sustained diabetes mellitus progresses to various complications, such as vascular disease, eye disease, kidney illness, diabetic foot, and others (Duarte et al. 2020). Excessive glucose in diabetes patients can be degraded into a potential precursor of overproduction of free radicals and—sooner or later— oxidative stress, which contributes to the aforementioned complications (Ji et al. 2021). Presently, oral synthetic diabetic agents such as acarbose, voglibose, and miglitol are used to treat type-2 DM that regrettably cause side effects, including flatulence, diarrhea, and abdominal disorder (Wang et al. 2022). Inhibition of α-glucosidase is