Fungal Bergamotane Sesquiterpenoids—Potential Metabolites: Sources, Bioactivities, and Biosynthesis

The marine environment represents the largest ecosystem on the Earth’s surface. Marine-derived fungi are of remarkable importance as they are a promising pool of diverse classes of bioactive metabolites. Bergamotane sesquiterpenoids are an uncommon class of terpenoids. They possess diverse biological properties, such as plant growth regulation, phototoxic, antimicrobial, anti-HIV, cytotoxic, pancreatic lipase inhibition, antidiabetic, anti-inflammatory, and immunosuppressive traits. The current work compiles the reported bergamotane sesquiterpenoids from fungal sources in the period ranging from 1958 to June 2022. A total of 97 compounds from various fungal species were included. Among these metabolites, 38 compounds were derived from fungi isolated from different marine sources. Furthermore, the biological activities, structural characterization, and biosynthesis of the compounds are also discussed. The summary in this work provides a detailed overview of the reported knowledge of fungal bergamotane sesquiterpenoids. Moreover, this in-depth and complete review could provide new insights for developing and discovering new valuable pharmaceutical agents from these natural metabolites.


Introduction
Nature has substantially participated in the discovery of drugs for human remedial treatments since the beginning of mankind [1]. The marine environment, with more than 70% of the surface of the Earth, represents the largest ecosystem and is characterized by quite variable physicochemical parameters (e.g., limited light access, low temperature, high pressure, and high salinity) [2]. Among the various marine microbes, fungi are a superabundant and ecologically substantial component of marine microbiota [3]. Fungi are one of nature's treasures that inhabit various environments on the earth's surface, including the marine environment [4][5][6][7]. They play a growing relevant role in drug development and biomedicine research, either directly as drugs or indirectly as lead structures for bio-inspired drug synthesis [8][9][10][11][12]. In the last decades, natural product chemists and pharmacologists have turned their research interests to marine-derived fungi, which are renowned as a vast unexploited reservoir of metabolic diverseness and found to have the capability to produce structurally unique bio-metabolites [6,7,[12][13][14][15][16]. Furthermore, research on fungiderived metabolites has tremendously increased because of the need for compounds with potential economical values and pharmaceutical applications. Sesquiterpenes belonging to various classes, including hirsutane, alliacane, tremulane, bergamotane, drimane, etc., Table 1. Naturally occurring fungal bergamotane sesquiterpenoids (name, source, extract/fraction, molecular weights and formulae, and location).

Compound Name
Fungal Source/Host Extract/Fraction Mol. Wt.

Mol. Formula
Location Ref.
Bicyclic Bergamotane Sesquiterpenoids Surveying their bioactivities may open a new research area for the synthesis of new agents from these metabolites by synthetic and medicinal chemists. The literature search for the reported data was performed using diverse databases and publishers, including Web of Science, Google Scholar, PubMed, Scopus, SciFinder, Wiley, SpringerLink, and ACS Publications, using specific keywords (bergamotane, marine, fungi, biosynthesis, and biological activities).

Structural Assignment and Stereochemistry Determination
A total of 97 metabolites have been separated from various fungal source extracts using different chromatographic techniques and characterized by NMR, MS, and IR spectral analyses as well as chemical derivatization. The relative configuration of these metabolites was established using NOESY or ROESY spectral analyses. Various studies reported the assigning of their absolute stereochemistry using total synthesis [53,54], Mosher's method [26], X-ray diffraction, chemical conversion [34,43,55], and ECD analyses [31]. The reported metabolites have been categorized into bi-, tri-, and tetracyclic derivatives.

Biological Activities of Bergamotane Sesquiterpenoids
Various reported studies revealed the assessment of bergamotane sesquiterpenoids for diverse bioactivities, including plant growth regulation, phototoxic, antimicrobial, anti-HIV, cytotoxic, pancreatic lipase inhibition, antidiabetic, anti-inflammatory, and immunosuppressive, which were summarized in this work (Table 2). Additionally, the reported structure-activity relation was included.   3.1. Anti-Inflammatory Activity NO (nitric oxide) is a substantial pro-inflammatory mediator, and its excessive production is accompanied with various inflammatory illnesses; therefore, it possesses a remarkable role for regulating immune responses and inflammation [56]. NO production inhibitors may represent the potential capacity for treating various inflammatory disorders. Thus, further research for fungal metabolites must be conducted to discover novel anti-inflammation agents.
The epigenetic chemical manipulation of Eutypella sp. derived from deep-sea hydrothermal sulfide deposit by co-treatment with SBHA (histonedeacetylase inhibitor, suberohydroxamic acid) and 5-Aza (DNA methyltransferase inhibitor, 5-azacytidine) was shown to activate a biosynthetic sesquiterpene-linked gene cluster [35]. From elicitortreated cultures EtOAc extract, eutypeterpenes A-F (18-22 and 28) along with xylariterpenoids A (16) and B (17) were purified using SiO 2 /RP-18/HPLC that were identified by spectral analyses, as well as by using chemical conversion, X-ray diffraction, ECD, and calculated NMR for configuration assignments.
Eutypeterpene A (28) is the first bergamotene sesquiterpene incorporating a dioxolanone moiety. These metabolites were assessed for their NO production inhibitory capacity induced by LPS-(lipopolysaccharide) in RAW 264.7 macrophages [35]. The results indicated thatcompound 18 and 19 (IC 50 13.4 and 16.8 µM, respectively) displayed more effectiveness than quercetin (IC 50 of 17.0 µM), whereas other metabolites had noticeable potentials (IC 50 values ranged from 18.7 to 24.3 µM) with weak cytotoxic capacities (IC 50 > 100 µM). A structure-activity study revealed that the analog with a triol unit (18) at the side chain was more effective than compound 16, 17, and 19 with a diol unit, which were more potent than compound 20, 21, and 28 with one hydroxy group. Furthermore, the α,β-unsaturated ketone unit (as in compound 21 and 22) and the OH-linked carbon configuration also affected the activities (16 versus 17) [35] (Figure 1).  Biogenetically, compounds 18-22 are derived from FPP that performs a 1,6-cyclization to produce bisabolane (A). The 4,7-cyclization of A generates bergamotane (B), which further generates 18-22 via diverse oxidation and reduction processes. Additionally, compound 28 is formed from 18 by carbonate incorporation [35] (Scheme 1).

Phytotoxic Activity
Prehelminthosporol (38) and dihydroprehelminthosporol (34) along with compounds 35-37, 39, 40, and 43 were separated by SiO 2 , flash CC, and preparative TLC from the EtOAc extract of the Bipolaris species, which is a Sorghum halepnse (Johnson grass) pathogen ( Figure 3). These metabolites were assessed for their phytotoxic potential towards Sorghum bicolor (Sorghum) and Sorghum balepense (Johnson grass) in leaf spot assays [36,37]. Compounds 34, 38, and 39 produced similar lesions to those caused by the fungus in the field. The lesions appeared as a reddish-brown area (0.3-0.5 cm diameter) surrounded by a black circle with an outer chlorotic zone. Compounds 34 and 38 (concentration of 25 µg/5 µL) had comparable toxic effectiveness, while compound 38 maintained its effect at a lower concentration of 2.5 µg/5 µL; meanwhile, the other compounds were non-toxic [36,37]. Victoxinine was also toxic to cereals in the order of oats > rye and barley > wheat > sorghum in a root inhibition assay [37]. The phytotoxic influence of compounds 34 and 38-40 versus sorghum, corn, bent-grass, sickle-pod, and morning glory was also assessed in leaf spot assays. Moreover, victoxinine caused a water-soaked translucent appearance with defined irregular necrotic edges. It is worth mentioning that 3-deoxyanthocyanidins are sorghum stress response metabolites (phytoalexins), which were accountable for the red wound response. Compounds 34, 38, and 39 were elicitors of a very strong reddening compared with the wounding-produced reddening, but compound 40 did not elicit a sorghum phytoalexin response. In bent grass and corn, compounds 34 and 38-40 produced a light-brown area limited by a chlorotic region, whereas in sickle pod and morning glory, they showed necrotic lesions that extended at high concentrations beyond the under-drop area. It is noteworthy that compound 38 was the most toxic compound versus all tested plants except for the morning glory [37].

Phytotoxic Activity
Prehelminthosporol (38) and dihydroprehelminthosporol (34) along with compounds 35-37, 39, 40, and 43 were separated by SiO2, flash CC, and preparative TLC from the EtOAc extract of the Bipolaris species, which is a Sorghum halepnse (Johnson grass) pathogen ( Figure 3). These metabolites were assessed for their phytotoxic potential towards Sorghum bicolor (Sorghum) and Sorghum balepense (Johnson grass) in leaf spot assays [36,37]. Compounds 34, 38, and 39 produced similar lesions to those caused by the fungus in the field. The lesions appeared as a reddish-brown area (0.3-0.5 cm diameter) surrounded by a black circle with an outer chlorotic zone. Compounds 34 and 38 (concentration of 25 µg/5 µL) had comparable toxic effectiveness, while compound 38 maintained its effect at a lower concentration of 2.5 µg/5 µL; meanwhile, the other compounds were non-toxic [36,37]. Victoxinine was also toxic to cereals in the order of oats > rye and barley > wheat > sorghum in a root inhibition assay [37]. The phytotoxic influence of compounds 34 and 38-40 versus sorghum, corn, bent-grass, sickle-pod, and morning glory was also assessed in leaf spot assays. Moreover, victoxinine caused a water-soaked translucent appearance with defined irregular necrotic edges. It is worth mentioning that 3-deoxyanthocyanidins are sorghum stress response metabolites (phytoalexins), which were accountable for the red wound response. Compounds 34, 38, and 39 were elicitors of a very strong reddening compared with the wounding-produced reddening, but compound 40 did not elicit a sorghum phytoalexin response. In bent grass and corn, compounds 34 and 38-40 produced a light-brown area limited by a chlorotic region, whereas in sickle pod and morning glory, they showed necrotic lesions that extended at high concentrations beyond the under-drop area. It is noteworthy that compound 38 was the most toxic compound versus all tested plants except for the morning glory [37]. Helminthosporium victoriae, the causative agent of oats Victoria blight disease yielded phytotoxins, victoxinine (40) and victoxinine α-glycerophosphate (41), which were separated from its diethyl ether extract using Sephadex LH-20 and SiO2 CC and detected on the TLC plate by giving a blue color with 5% vanillin:H2SO4 [41] (Figure 4). The existence Helminthosporium victoriae, the causative agent of oats Victoria blight disease yielded phytotoxins, victoxinine (40) and victoxinine α-glycerophosphate (41), which were separated from its diethyl ether extract using Sephadex LH-20 and SiO 2 CC and detected on the TLC plate by giving a blue color with 5% vanillin:H 2 SO 4 [41] (Figure 4). The existence of α-glycerophosphate moiety was established by coupling between the phosphorous and carbon. Compound 40 completely prohibited the root growth of toxin-susceptible and toxin-resistant oats (concentration of 2.5 × 10 −4 M); it was ≈ 7500 times more toxic for susceptible plants on a weight basis, while its toxicity for resistant plants was nearly similar, suggesting a role of the victoxinine moiety on the toxicity [38,39,41]. On the other side, compound 41 (concentration of 100 µg/mL) demonstrated little or no growth inhibition effectiveness on either susceptible or resistant oats [41]. Helminthosporium victoriae, the causative agent of oats Victoria blight disease yielded phytotoxins, victoxinine (40) and victoxinine α-glycerophosphate (41), which were separated from its diethyl ether extract using Sephadex LH-20 and SiO2 CC and detected on the TLC plate by giving a blue color with 5% vanillin:H2SO4 [41] (Figure 4). The existence of α-glycerophosphate moiety was established by coupling between the phosphorous and carbon. Compound 40 completely prohibited the root growth of toxin-susceptible and toxin-resistant oats (concentration of 2.5 × 10 −4 M); it was ≈ 7500 times more toxic for susceptible plants on a weight basis, while its toxicity for resistant plants was nearly similar, suggesting a role of the victoxinine moiety on the toxicity [38,39,41]. On the other side, compound 41 (concentration of 100 µg/mL) demonstrated little or no growth inhibition effectiveness on either susceptible or resistant oats [41].    [43]. Biogenetically, they were derived from the mevalonate/trans-cis-farnesol/bisabolene/bergamotane pathway (Scheme 2).

Immunosuppressive Activity
Immunosuppressants are drugs that prohibit body immunity and are principally utilized in organ transplantation to overcome rejection and in auto-immune illnesses [57]. Currently, many immunosuppressive agents act by prohibiting T-cell proliferation; however, there is no new, safe, and efficient immune-suppressive agent that prohibits B-cell proliferation [58].

Antimicrobial Activity
From Podospora decipiens, two new tetracyclic sesquiterpenoids, decipienolides A (74) and B (75), were separated from the EtOAc extract by SiO2 CC and HPLC analyses. They were obtained as a mixture of inseparable epimers, having a 3-hydroxy-2,2-dimethylbutyric acid sidechain as elucidated by an NMR analysis (Figure 8). The 74/75 mixture had an antibacterial influence versus B. subtilis (inhibition zone diameter of 9-10 mm, . Structurally, it was noted that the α,β-unsaturated-carboxylic acid unit could be the key functional group for the immunosuppressive potential of these metabolites. Furthermore, compounds 61 and 7-10 with a β-pinene main core had a wider range of bioactivities [30].

Antimicrobial Activity
From Podospora decipiens, two new tetracyclic sesquiterpenoids, decipienolides A and B (75), were separated from the EtOAc extract by SiO2 CC and HPLC analyses. were obtained as a mixture of inseparable epimers, having a 3-hydroxy-2,2-dime butyric acid sidechain as elucidated by an NMR analysis (Figure 8). The 74/75 mixtur an antibacterial influence versus B. subtilis (inhibition zone diameter of 9-10

Pancreatic Lipase Inhibition
Purpurolides B (83) and C (84) are new 6/4/5/5-tetracyclic sesquiterpenoids that were separated from Penicillium purpurogenum IMM003 cultures by SiO2/RP-18/preparative HPLC analysis. The structures and configurations of compounds 83 and 84 were established using spectral and X-ray analyses as well as ECD and GIAO NMR data calculations (Figure 9).

Immunosuppressive Activity
Immunosuppressants are drugs that prohibit body immunity and are princip lized in organ transplantation to overcome rejection and in auto-immune illnes Currently, many immunosuppressive agents act by prohibiting T-cell proliferatio ever, there is no new, safe, and efficient immune-suppressive agent that prohib proliferation [58].

Antidiabetic Activity
From the deep sea-derived Paraconiothyrium brasiliense HDN15-135 EtOAc extract, new bergamotane sesquiterpenoids, brasilterpenes A-E (66-70), featuring an uncommon 6/4/5-tricyclic ring system, were separated by SiO 2 /RP-18/Sephadex LH-20/HPLC and assigned by diverse NMR analyses and X-ray diffraction, ECD, and DFT-NMR (density functional theory calculations of nuclear magnetic resonance) data [45]. Their hypoglycemic potential was estimated utilizing β-cell-ablated zebrafish larvae. Compounds 66 and 68 (concentration of 10 µM) remarkably lessened the glucose level down to 449.3 and 420.4 pmol/larva respectively, compared with the β-cell-ablated group (Teton+) (glucose level of 502.8 pmol/larva) and rosiglitazone (glucose level 395.6 pmol/larva) with no toxic influence on zebrafish larvae up to 200 µM. It was found that compounds 66 and 68 notably minimized free blood glucose in vivo in hyperglycemic zebrafish by suppressing gluconeogenesis and improving insulin sensitivity, which revealed that compound 68 had promising antidiabetic potential [45]. The structure-activity study revealed that the activity may be linked to the C-14 S-configuration of compounds 66 and 68, which represent the main structural difference from 67 and 69. The existence of C-3-OH may weaken the influence in 68 versus 66; however, the 2 endocyclic double bond may enhance the potential in 70 versus 69 [45]. Therefore, compound 68 may provide a scaffold for hypoglycemic drug development. Compounds 66-70 are also biosynthesized by the FPP pathway (Scheme 4). The cyclization of FPP via NPP (nerolidyl diphosphate) followed by a bisabol intermediate yields the bergamotane skeleton. These compounds are created by further oxidation, 9-OH-nucleophilic attack, and methylation processes. Because of the nucleophilic attack direction flexibility during the furan ring formation, compounds 66-69 appeared as C14-epimers in pairs [45] (Scheme 4). Compounds 83 and 84 demonstrated potent pancreatic lipase inhibition (IC50s of 5.45 and 6.63 µM, respectively), compared with kaempferol (IC50 of 1.50 µM) [47]. These compounds were possibly biosynthesized via numerous the cyclization and enzyme-catalyzed oxidation of FPP (farnesyl pyrophosphate), leading to four-and six-membered rings and the formation of two five-membered heterocyclic rings (Scheme 3) [47].  Ying et al. isolated two new derivatives, expansolides C (73) and D (81), in addition to 72 and 80 from the plant pathogen Penicillium expansum ACCC37275 [46]. In an αglucosidase inhibition assay; the 73/81 epimeric mixture (ratio 2:1) possessed a more powerful effectiveness (IC 50 of 0.50 mM) compared with acarbose (IC 50 1.90 mM), while the 72/80 epimeric mixture possessed no apparent potential. It was assumed that the acetyl group in compounds 72 and 80 impeded their binding with the α-glucosidase, resulting in loss of activity [46].

Plant Growth Regulation
Kimura et al. purified the tricyclic amide sesquiterpenoid pinthunamide (44) from the acetone extract of Ampulliferina sp. at pH 2.0 utilizing SiO 2 and sephadex LH20 CC processing as well as crystallization from EtOAc extract, which gave positive NH 2 OH-HCI-FeCl 3 and KMnO 4 reactions [42]. The compound was assigned by X-ray diffraction and NMR methods. Its plant growth regulation effectiveness was evaluated using a lettuce seedling assay, where it (dose 300 mg/L) produced a 150% root growth acceleration over the control seedlings (100%) while scarcely influencing the hypocotyl elongation at the tested concentrations [42]. Its structure combined a unique configuration of six-, five-, and four-membered rings that was proposed to be biosynthesized via the mevalonate/trans-cisfarnesol/bisabolene/bergamotane pathway (Scheme 5) [42]. neogenesis and improving insulin sensitivity, which revealed that compound 68 had promising antidiabetic potential [45]. The structure-activity study revealed that the activity may be linked to the C-14 S-configuration of compounds 66 and 68, which represent the main structural difference from 67 and 69. The existence of C-3-OH may weaken the influence in 68 versus 66; however, the △ 2 endocyclic double bond may enhance the potential in 70 versus 69 [45]. Therefore, compound 68 may provide a scaffold for hypoglycemic drug development. Compounds 66-70 are also biosynthesized by the FPP pathway (Scheme 4). The cyclization of FPP via NPP (nerolidyl diphosphate) followed by a bisabol intermediate yields the bergamotane skeleton. These compounds are created by further oxidation, 9-OH-nucleophilic attack, and methylation processes. Because of the nucleophilic attack direction flexibility during the furan ring formation, compounds 66-69 appeared as C14-epimers in pairs [45] (Scheme 4).  Ying et al. isolated two new derivatives, expansolides C (73) and D (81), in additi to 72 and 80 from the plant pathogen Penicillium expansum ACCC37275 [46]. In an α-g cosidase inhibition assay; the 73/81 epimeric mixture (ratio 2:1) possessed a more pow ful effectiveness (IC50 of 0.50 mM) compared with acarbose (IC50 1.90 mM), while the 72 epimeric mixture possessed no apparent potential. It was assumed that the acetyl gro in compounds 72 and 80 impeded their binding with the α-glucosidase, resulting in lo of activity [46].

Plant Growth Regulation
Kimura et al. purified the tricyclic amide sesquiterpenoid pinthunamide (44) fro the acetone extract of Ampulliferina sp. at pH 2.0 utilizing SiO2 and sephadex LH20 C processing as well as crystallization from EtOAc extract, which gave positive NH2O HCI-FeCl3 and KMnO4 reactions [42]. The compound was assigned by X-ray diffracti and NMR methods. Its plant growth regulation effectiveness was evaluated using a l tuce seedling assay, where it (dose 300 mg/L) produced a 150% root growth accelerati over the control seedlings (100%) while scarcely influencing the hypocotyl elongation the tested concentrations [42]. Its structure combined a unique configuration of six-, fiv , and four-membered rings that was proposed to be biosynthesized via the meva nate/trans-cis-farnesol/bisabolene/bergamotane pathway (Scheme 5) [42]. . They were stereoisomers that had γ-lactam rings. Additionally, they (doses of 300 a 30 mg/L) were shown to promote lettuce seedling root growth by 200% over the cont lettuce seedlings (100%) [50]. In 1993, the same group separated a minor metabolite, dih droampullicin (93), characterized by the absence of the C8-C9 double bond. The co pound promoted a 160% growth rate in lettuce seedling roots (dose of 300 mg/L) co pared with the control; however, it had no influence on the hypocotyl growth, indicati that the C8-C9-double bond (C8-C9) was substantial in lettuce seedlings` root growth [5 Bermejo et al. reported the synthesis of (+)−91 and 92 from (R)-(-)-carvone with a 4. Furthermore, in 1990, Kimura et al. purified another two new plant growth regulators, ampullicin (91) and isoampullicin (92) from Ampulliferina sp. No. 27 associated with Pinus thunbergii dead tree by SiO 2 CC utilizing benzene:acetone as an eluent [50] (Figure 10). They were stereoisomers that had γ-lactam rings. Additionally, they (doses of 300 and 30 mg/L) were shown to promote lettuce seedling root growth by 200% over the control lettuce seedlings (100%) [50]. In 1993, the same group separated a minor metabolite, dihydroampullicin (93), characterized by the absence of the C8-C9 double bond. The compound promoted a 160% growth rate in lettuce seedling roots (dose of 300 mg/L) compared with the control; however, it had no influence on the hypocotyl growth, indicating that the C8-C9-double bond (C8-C9) was substantial in lettuce seedlings' root growth [51]. Bermejo et al. reported the synthesis of (+)−91 and 92 from (R)-(-)-carvone with a 4.5% overall yield using a stereo-selective 18-step sequence application [59]. The EtOAc extract of Aspergillus fumigatus Fresenius separated from leaf litter yielded expansolides A (72) and B (80). They had 2S/4S/6S/7R/9R/11S and 2S/4R/6S/7R/9R/11S, respectively, based on modified Mosher's method. The compounds noticeably prohibited etiolated wheat coleoptiles growth by 100% and 59% at 10 −3 M and 10 −4 M solution compared with LOGRAN (commercial herbicide) (%inhibition of 80 and 42%) at the same concentrations [26].

Cytotoxic Activity
Compounds 3 and 4, which were new β-bergamotane sesquiterpenoids, were sep rated by SiO2/RP-18/HPLC from the marine-associated Aspergillus fumigatus-YK-7 EtOA extract. Their antiproliferative effects on the U937 and PC-3 cell lines were measured vitro in an MTT assay. Compound 4 revealed a weak growth inhibition capacity (IC50 84.9 µM) versus the U937 cell line, while 3 had no activity (IC50 > 100 µM) compared wi doxorubicin hydrochloride (IC50 of 0.021 µM). On the other sides, both had no effect ve sus PC-3 cells [29]. Wu et al. reported the separation of two new derivatives, xylariterp noids A and B (16 and 17), from the EtOAc extract of Xylariaceae fungus by Sephadex LH 20/ODS CC and reversed-phase HPLC processing [33]. Their structures and stereo-co figuration were proved utilizing NMR and CD methods. They are C-10 epimers havin
The chemical investigation of Arctic fungus Eutypella sp. D-1 s EtOAc extract yielded new derivatives, eutypellacytosporins A-D (94-97), which were established by spectroscopic analysis and modified Mosher's method. Structurally, these metabolites are related to decipienolides and cytosporins. They exhibited (IC 50 s ranging from 4.9 to 17.1 µM) weak-to-moderate cytotoxic influence versus DU145, SW1990, Huh7, and PANC-1 in the CCK-8 assay, whereas Huh7 and SW1990 cell lines had more sensitivity to 94-97 (IC 50 s ranging from 4.9 to 8.4 µM). On the other hand, compounds 95 and 97 possessed noticeable potential versus PANC-1 (IC 50 s of 7.9 and 7.5 µM, respectively) compared with cisplatin (IC 50 4.5 µM). The results revealed that the decipienolide moiety was substantial for activity; however, the C-33 configuration did not affect the activity [52]. It was proposed that compounds 94-97 are created from gentisaldehyde precursor with subsequent isoprenyl unit addition, double bond epoxidation, keto group hydrogenation, and an aliphatic chain addition (Scheme 6). The other precursor, the 14-OH of decipienolide A 74 or B 75, is produced from hydroxylation, allylic oxidation, and cyclization of farnesyl diphosphate to give I with a bicycle[3.1.1]heptane. Additionally, (14S)-14-OH-expansolide C, (14R)-14-OH-expansolide C, (14S)-14-OH-expansolide D, and (14R)-14-OH-expansolide D are formed via two steps of reface-and si-face attacks of the OH groups on the ketone and aldehyde groups, respectively. After these steps, compounds 94-97 were produced from the two groups of 14-OH-expansolides C and D through condensation reactions with (S)-3-hydroxy-2,2-dimethylbutanoic acid and cytosporin D, respectively [52].

Conclusions
Fungal metabolites are an unparalleled pool for pharmaceutical lead discovery. Sesquiterpenoids involving the bergamotane skeleton have been separated from various sources, including fungi. In the current work, 97 bergamotane sesquiterpenoids were reported from various fungal species derived from different sources, including endophytic (24 compounds), mushroom (21 compounds), sea mud (14 compounds), sea sediment (13 compounds), deep-sea deposit (8 compounds), and sponges (3 compounds) ( Figure 11). The majority of compounds have been reported from Paraconiothyrium (25 com pounds), Craterellus (23 compounds), and Eutypella (12 compounds) species (Figure 12 Interestingly, many of these metabolites normally occurred as inseparable mixtures. Thes metabolites were assessed for diverse bio-activities. It is obvious that cytotoxic evaluatio accounts for the largest proportion of biological assessments, where they had weak or n effectiveness on the tested cell lines. On the other hand, there are limited reports on the phytotoxic, plant growth regulation, antimicrobial, anti-HIV, cytotoxic, anti-inflamma tory, pancreatic lipase inhibition, immunosuppressive, and antidiabetic activities. There fore, this suggested more potential for trying other types of pharmacological effectivenes Victoxinine (40) and prehelminthosporolactone (39) displayed potential phytotoxic capac ities; therefore, they could be utilized as bioherbicides or as lead metabolites for synthe sizing more efficacious phytotoxic compounds against various weeds. Pinthunamide (44 ampullicin (91), isoampullicin (92), and dihydroampullicin (93) were found to selectivel promote the root growth. However, the phytotoxic and plant growth promotion potentia should be transferred from laboratory experiments into field settings for assessing the en vironmental influences on these activities. Purpurolide F (87) had potent pancreatic lipas inhibition potential that could be a viable candidate as a pancreatic lipase inhibitor fo further clinical development. Massarinolin B (61) had prominent immunosuppressive po tential, suggesting further in vivo and mechanistic investigations for the development o this metabolite as an immunosuppressant. In silico studies for the reported metabolite that have not been tested or have had no noticeable effectiveness in the estimated activitie could be a possible area of future research. Moreover, synthesis and structural modifica tions of these metabolites may produce more potential and useful tags of these metabolite through click chemistry, which is a new approach for synthesizing drug-like molecule that can boost the drug discovery process. The majority of compounds have been reported from Paraconiothyrium (25 compounds), Craterellus (23 compounds), and Eutypella (12 compounds) species ( Figure 12). Interestingly, many of these metabolites normally occurred as inseparable mixtures. These metabolites were assessed for diverse bio-activities. It is obvious that cytotoxic evaluation accounts for the largest proportion of biological assessments, where they had weak or no effectiveness on the tested cell lines. On the other hand, there are limited reports on their phytotoxic, plant growth regulation, antimicrobial, anti-HIV, cytotoxic, anti-inflammatory, pancreatic lipase inhibition, immunosuppressive, and antidiabetic activities. Therefore, this suggested more potential for trying other types of pharmacological effectiveness. Victoxinine (40) and prehelminthosporolactone (39) displayed potential phytotoxic capacities; therefore, they could be utilized as bioherbicides or as lead metabolites for synthesizing more efficacious phytotoxic compounds against various weeds. Pinthunamide (44), ampullicin (91), isoampullicin (92), and dihydroampullicin (93) were found to selectively promote the root growth. However, the phytotoxic and plant growth promotion potential should be transferred from laboratory experiments into field settings for assessing the environmental influences on these activities. Purpurolide F (87) had potent pancreatic lipase inhibition potential that could be a viable candidate as a pancreatic lipase inhibitor for further clinical development. Massarinolin B (61) had prominent immunosuppressive potential, suggesting further in vivo and mechanistic investigations for the development of this metabolite as an immunosuppressant. In silico studies for the reported metabolites that have not been tested or have had no noticeable effectiveness in the estimated activities could be a possible area of future research. Moreover, synthesis and structural modifications of these metabolites may produce more potential and useful tags of these metabolites through click chemistry, which is a new approach for synthesizing drug-like molecules that can boost the drug discovery process. Biogenetically, these metabolites are generated from acyclic farnesyl-diphosphate which undertakes various condensation and rearrangement reactions. This work could b a beneficial reference for researchers studying this class of fungal metabolites. Severa strategies, including co-culture, molecular and epigenetic manipulations, OSMAC (on strain many compounds), heterologous gene expression, and inter-species cross-talk ap proaches could be successively employed to access undescribed natural metabolites from silent biosynthetic pathways. It was found that the selective epigenetic target manipula tion utilizing small molecule inhibitors toward DNA methyltransferase and histon deacetylase activities resulted in the enhancement of biosynthetic pathway expression fo new secondary metabolite production. Highlighting the biosynthesis of these metabolite in this review could draw the attention of molecular biologists and genetics-interested researchers for isolating genes accountable for the biosynthesis of these interesting metab olites; this could allow for the discovery of the detailed mechanisms of their formation b various enzymes, which could allow for the preparation these metabolites and their ana logs by engineering their biosynthetic pathways.   Biogenetically, these metabolites are generated from acyclic farnesyl-diphosphate, which undertakes various condensation and rearrangement reactions. This work could be a beneficial reference for researchers studying this class of fungal metabolites. Several strategies, including co-culture, molecular and epigenetic manipulations, OSMAC (one strain many compounds), heterologous gene expression, and inter-species cross-talk approaches could be successively employed to access undescribed natural metabolites from silent biosynthetic pathways. It was found that the selective epigenetic target manipulation utilizing small molecule inhibitors toward DNA methyltransferase and histone deacetylase activities resulted in the enhancement of biosynthetic pathway expression for new secondary metabolite production. Highlighting the biosynthesis of these metabolites in this review could draw the attention of molecular biologists and genetics-interested researchers for isolating genes accountable for the biosynthesis of these interesting metabolites; this could allow for the discovery of the detailed mechanisms of their formation by various enzymes, which could allow for the preparation these metabolites and their analogs by engineering their biosynthetic pathways.