Novel biotransformation processes of dihydroartemisinic acid and artemisinic acid to their hydroxylated derivatives by two plant cell culture systems

Biotransformation of sesquiterpenoids: a recent insight

Sesquiterpenoids have been identified as natural compounds showing remarkable biological activities found in medicinal plants. There is great interest in developing methods to obtain sesquiterpenoids derivatives and biotransformation is one of the alternative methods for structural modification of complex sesquiterpenes structures. Biotransformation is a great drug design tool offering high selectivity and green method. The present review describes a comprehensive summary of biotransformation products of sesquiterpenoids and its structural modification utilizing a variety of biocatalysts including microorganisms, plant tissue culture and enzymes. This review covers recent literatures from 2007 until 2020 and highlights the experimental conditions for each biotransformation process.

Biotransformation of artemisinic acid to bioactive derivatives by endophytic Penicillium oxalicum B4 from Artemisia annua L

As a biosynthetic precursor of the antimalarial drug artemisinin, artemisinic acid (AA) is abundant in Artemisia annua L. with a content of 8-10-fold higher than artemisinin, but less effective. In this study, the biotransformation of AA was carried out with an endophytic fungus Penicillium oxalicum B4 to extend its utility. After 10-day-culture of the endophyte with AA at 2 mg/mL, eight biotransformation metabolites were isolated from the culture broth, including five undescribed metabolites, namely 3α,14-dihydroxyartemisinic acid, 14-hydroxy-3-oxo-artemisinic acid, 15-hydroxy-3-oxo-artemisinic acid, 12, 15-artemisindioic acid and 1,2,3,6-tetradehydro-12, 15-artemisindioic acid. The fungal enzymes possess the selective capacity to hydroxylate, carbonylate and ketonize the allyl group of AA. The major biotransformation metabolite was the hydroxylated product 3-α-hydroxyartemisinic acid (33.3%) in the cultures of early stage (day 1-6), whereas most of the other biotransformation products were synthesized in the later stage (day 8-10). Compared with AA, some metabolites (3α,14-dihydroxyartemisinic acid, 15-hydroxy-3-oxo-artemisinic acid and 1,2,3,6-tetradehydro-12, 15-artemisindioic acid) possessed stronger cytotoxic activity to the human colon carcinoma cell line (LS174T) and promyelocytic leukemia cell line (HL-60). The metabolites 12, 15-artemisindioic acid and 3-α-hydroxyartemisinic acid exhibited significant inhibitory activity to the lipopolysaccharide-induced nitrite production of RAW 264.7 cells at 10.00 μM and 2.50 μM, respectively. The results demonstrated the potential of fungal endophytes on biotransforming AA to its bioactive derivatives.

Synthesis of [3,3-2H2]-Dihydroartemisinic Acid to Measure the Rate of Nonenzymatic Conversion of Dihydroartemisinic Acid to Artemisinin

Dihydroartemisinic acid is the biosynthetic precursor to artemisinin, the endoperoxide-containing natural product used to treat malaria. The conversion of dihydroartemisinic acid to artemisinin is a cascade reaction that involves C-C bond cleavage, hydroperoxide incorporation, and polycyclization to form the endoperoxide. Whether or not this reaction is enzymatically controlled has been controversial. A method was developed to quantify the nonenzymatic conversion of dihydroartemisinic acid to artemisinin using LC-MS. A seven-step synthesis of 3,3-dideuterodihydroartemisinic acid (23) was accomplished beginning with dihydroartemisinic acid (1). The nonenzymatic rates of formation of 3,3-dideuteroartemisinin (24) from 3,3-dideuterodihydroartemisinic acid (23) were 1400 ng/day with light and 32 ng/day without light. Moreover, an unexpected formation of nondeuterated artemisinin (3) from 3,3-dideuterodihydroartemisinic acid (23) was detected in both the presence and absence of light. This formation of nondeuterated artemisinin (3) from its dideuterated precursor (23) suggests an alternative mechanistic pathway that operates independent of light to form artemisinin, involving the loss of the two C-3 deuterium atoms.

Natural sesquiterpenoids

This review covers the isolation, structural determination, synthesis and chemical and microbiological transformations of natural sesquiterpenoids. The literature from January to December 2012 is reviewed, and 471 references are cited.

Follow-up of natural products isolation

Follow-up of natural products isolation refers to re-isolation of compound(s) of interest in larger amounts for further pharmacological testing, conclusive structure elucidation, structure modifications to synthesize analogs for structure-activity relationships (SAR) studies, preformulation and formulation studies or clinical trials. In addition to conventional synthetic chemistry approaches, several other methodologies can be applied for following-up natural products isolation. This chapter outlines, with specific examples, various strategies and methods involved in follow-up of natural products isolation.