Novel Bioactive Natural Products from Marine-Derived Penicillium Fungi: A Review (2021–2023)

Marine-derived Penicillium fungi are productive sources of structurally unique and diverse bioactive secondary metabolites, representing a hot topic in natural product research. This review describes structural diversity, bioactivities and statistical research of 452 new natural products from marine-derived Penicillium fungi covering 2021 to 2023. Sediments are the main sources of marine-derived Penicillium fungi for producing nearly 56% new natural products. Polyketides, alkaloids, and terpenoids displayed diverse biological activities and are the major contributors to antibacterial activity, cytotoxicity, anti-inflammatory and enzyme inhibitory capacities. Polyketides had higher proportions of new bioactive compounds in new compounds than other chemical classes. The characteristics of studies in recent years are presented.


Introduction
Marine-derived fungi have a variety of medical applications due to their capability of generating various enzymes and antimicrobial agents [1].Since the first species Sphaeria posidoniae (Halotthia posidoniae) on the rhizome of the sea grass Posidonia oceanica was studied in 1846 [2], scientists have never stopped studying the natural products (NPs) of marine-derived fungi [3].The rapid development of marine bio-technology and everincreasing needs of clinic applications resulted in the emergence of marine natural products as alternative drug sources in the early 1990s [4] and the voluminous output in natural product research from the fungi isolated from different marine animals, seaweeds and sediments, with many new bioactive compounds being described each year [5].
As an essential part of marine micro-organisms, Penicillium fungi have received great attention among all marine-derived fungi, accounting for 22% of NPs of marine fungal origin, and play an important role in the discovery of marine natural products with bioactivities and novel structures [6].Several reviews on natural products isolated from marine-derived Penicillium species have been published [4,[6][7][8].A total of 390 new secondary metabolites from marine-derived Penicillium fungi were highlighted from 1991 to 2014 [6], and 188 new secondary metabolites were summarized from 2015 to 2020 [7].More than 200 cytotoxic or antitumor compounds isolated from marine Penicillium fungus were included from 1991 to 2017 [4].Newly reported alkaloids produced by marine-derived Penicillium species were offered from 2014 to 2018 [8].Recently, some remarkable achievements have been made in the study of marine-derived Penicillium fungi, including an MS/MS targeted molecular networking approach for the discovery of rare communesins [9], the investigation of the apoptosis mechanism of dicitrinone G from by the analyses of the protein-protein interaction (PPI) network and Western blot [10], and so on.These effective approaches have given rise to the generation of unique chemicals and huge biological diversity, making marine-derived Penicillium fungi a hotspot for utilization in the discovery of new drug leads.
A systematic review of the origins, structures, and bioactivities of 452 new NPs produced by marine-derived Penicillium species from January 2021 to December 2023 is provided in this review, based on 115 studies searching in the SciFinder database with marine-derived Penicillium as the key word, with English as the language.The review also covers fifty-one new marine natural products only described based on the HPLC-MS/MS analyses [9]; two previously reported marine natural products with significant new bioactivities [11,12], three known marine natural products supplied the structural NMR data [13][14][15], and two compounds were presented as new natural products [15,16], but their structures are not shown.In addition, due to the narrow publication timespan, seven pairs of new compounds possessing different structures were given the same trivial name, respectively.In this review, the first reported compounds were given the suffix a [17][18][19], and the other ones were given the suffix b [20,21].
Mar. Drugs 2024, 22, 191 9 of 36 from the co-culture of the deep-sea-derived fungi P. crustosum PRB-2 and P. fellutanum HDN14-323 along with two esterification products, penifellutins C (185) and D (186) (Figure 4).Penifellutins A (183) and B (184) showed obvious inhibitory activity on the liver hyperplasia of zebrafish larvae at a concentration of 10 μmol/L, while penifellutins C (185) and D (186) showed no activity, indicating that two carboxyls in the structure were important active sites [66].
derivatives (427-431) (Figure 10) were isolated from the mangrove-sediment-derived P. ludwigii SCSIO 41408.Alkane derivatives 429 and 431 exhibited obvious inhibitory activities against LPS-induced NF-kB with IC50 values of 10.7 and 21.5 μM, respectively.Moreover, in a further study of their effects on RANKL-induced osteoclastogenesis, alkane derivative 429 was found to be able to suppress the RANKL-induced osteoclast differentiation in BMMCs, with a concentration of 10 μM [80].The names and numbers of all new compounds according to their classes, the sources from which marine-derived Penicillium were isolated, the biological activities of new compounds, and corresponding references are listed in Table 1.

Statistical Analysis of New Natural Products from Marine-Derived Penicillium
Penicillium fungi can establish a good relationship with different marine organisms and marine environments.According to the statistical results, sediments and mangroves were the main sources or hosts of marine-derived Penicillium fungi for producing new natural products, nearly 56% (Figure 11).Penicillium fungi can establish a good relationship with different marine organisms and marine environments.According to the statistical results, sediments and mangroves were the main sources or hosts of marine-derived Penicillium fungi for producing new natural products, nearly 56% (Figure 11).The new natural products had diverse chemical structures including polyketides, alkaloids, terpenoids, steroids, peptides, and others.Figure 12 shows the proportion of new bioactive compounds in each chemical class.A total of 194, 107 and 107 new compounds belong to polyketides, alkaloids and terpenoids, respectively, adding up to more than 90% of the total.Similarly, these three classes contribute 94% of all new bioactive compounds.The highest proportion of bioactives belongs to the largest number of polyketides (86) with 44.3%, followed by terpenoids (41) with 39.3% and alkaloids (42) with 38.3%.The new natural products had diverse chemical structures including polyketides, alkaloids, terpenoids, steroids, peptides, and others.Figure 12 shows the proportion of new bioactive compounds in each chemical class.A total of 194, 107 and 107 new compounds belong to polyketides, alkaloids and terpenoids, respectively, adding up to more than 90% of the total.Similarly, these three classes contribute 94% of all new bioactive compounds.The highest proportion of bioactives belongs to the largest number of polyketides (86) with 44.3%, followed by terpenoids (41) with 39.3% and alkaloids (42) with 38.3%.Penicillium fungi can establish a good relationship with different marine organisms and marine environments.According to the statistical results, sediments and mangroves were the main sources or hosts of marine-derived Penicillium fungi for producing new natural products, nearly 56% (Figure 11).The new natural products had diverse chemical structures including polyketides, alkaloids, terpenoids, steroids, peptides, and others.Figure 12 shows the proportion of new bioactive compounds in each chemical class.A total of 194, 107 and 107 new compounds belong to polyketides, alkaloids and terpenoids, respectively, adding up to more than 90% of the total.Similarly, these three classes contribute 94% of all new bioactive compounds.The highest proportion of bioactives belongs to the largest number of polyketides (86) with 44.3%, followed by terpenoids (41) with 39.3% and alkaloids (42) with 38.3%.The new compounds were counted only once when they were analyzed for bioactivity or inactivity.If the article did not provide a description of strong, moderate or weak activity of bioactive compounds, we gave this description according to bioactivity potency criteria used in the review [124].The multi-active compounds were counted multiple times when they were classified according to anti-cancer/cytotoxicity, anti-inflammatory, antibacterial, antifungal, antiviral, enzyme inhibitory, antioxidant, and anti-allergy activities, as well as others [125].
Figure 13 shows the percentage distribution of new compounds with different bioactivities for 2021-2023.Among them, 24.3% of the new bioactive compounds showed antibacterial activity with the number of 44.This was followed by cytotoxic activity at 38 (21%), enzyme inhibition activity at 30 (16.6%), and anti-inflammatory activity at 27 (14.9%).
Mar. Drugs 2024, 22, x 29 of 36 The new compounds were counted only once when they were analyzed for bioactivity or inactivity.If the article did not provide a description of strong, moderate or weak activity of bioactive compounds, we gave this description according to bioactivity potency criteria used in the review [124].The multi-active compounds were counted multiple times when they were classified according to anti-cancer/cytotoxicity, antiinflammatory, antibacterial, antifungal, antiviral, enzyme inhibitory, antioxidant, and anti-allergy activities, as well as others [125].
Figure 13 shows the percentage distribution of new compounds with different bioactivities for 2021-2023.Among them, 24.3% of the new bioactive compounds showed antibacterial activity with the number of 44.This was followed by cytotoxic activity at 38 (21%), enzyme inhibition activity at 30 (16.6%), and anti-inflammatory activity at 27 (14.9%).Figure 14A shows the proportion distribution of new compounds with different bioactivities in each chemical class for 2021-2023; peptides are not listed due to the absence of activity results.Polyketides displayed antibacterial activity as the dominant activity with a proportion of 29%, highlighting that they encompass many potential antibacterial drug leads.For alkaloids, cytotoxic compounds accounted for 31.7% of the total active compounds, while terpenoids displayed relatively high enzyme inhibitory with a proportion of 21.4%.Figure 14B shows the proportion distribution of new compounds with different chemical classes in each bioactivity for 2021-2023.The major contributors to antibacterial activity are polyketides.The most promising anticancer/cytotoxicity agents from marine-derived Penicillium fungi appear to be alkaloids.The main anti-inflammatory and enzyme inhibitory metabolites are still polyketides.Figure 14A shows the proportion distribution of new compounds with different bioactivities in each chemical class for 2021-2023; peptides are not listed due to the absence of activity results.Polyketides displayed antibacterial activity as the dominant activity with a proportion of 29%, highlighting that they encompass many potential antibacterial drug leads.For alkaloids, cytotoxic compounds accounted for 31.7% of the total active compounds, while terpenoids displayed relatively high enzyme inhibitory with a proportion of 21.4%.Figure 14B shows the proportion distribution of new compounds with different chemical classes in each bioactivity for 2021-2023.The major contributors to antibacterial activity are polyketides.The most promising anti-cancer/cytotoxicity agents from marine-derived Penicillium fungi appear to be alkaloids.The main anti-inflammatory and enzyme inhibitory metabolites are still polyketides.
It should be noted that not all new metabolites isolated from the marine-derived Penicillium fungi were tested for biological activity because of scarcity of quantity [37,52,59,79,92], while many bioactive compounds were only studied for one type of bioassay.In addition, most of the biological activities of the experimental subjects are performed in vitro.Correspondingly, bioactive assays in vivo are only applied in a few studies, for example, zebrafish models used for investigations into anti-cancer/cytotoxicity [66], anti-angiogenesis [86,121], and hypoglycemia [122].Furthermore, the difficulty of the biological screening model was another factor affecting the screening result.In fact, viruses were not considered as screening targets in general laboratory due to inherent complexity of cell-based assays of viruses [125], while mice models were expensive and time consuming.Therefore, more new natural products from the marine-derived Penicillium fungi should be screened on a wider variety of bioassays, as effective enrichment of trace compounds and enhanced methods in bioactivity screening technologies are important.It should be noted that not all new metabolites isolated from the marine-derived Penicillium fungi were tested for biological activity because of scarcity of quantity [37,52,59,79,92], while many bioactive compounds were only studied for one type of bioassay.In addition, most of the biological activities of the experimental subjects are performed in vitro.Correspondingly, bioactive assays in vivo are only applied in a few studies, for example, zebrafish models used for investigations into anticancer/cytotoxicity [66], anti-angiogenesis [86,121], and hypoglycemia [122].Furthermore, the difficulty of the biological screening model was another factor affecting the screening result.In fact, viruses were not considered as screening targets in general laboratory due to inherent complexity of cell-based assays of viruses [125], while mice models were expensive and time consuming.Therefore, more new natural products from the marinederived Penicillium fungi should be screened on a wider variety of bioassays, as effective enrichment of trace compounds and enhanced methods in bioactivity screening technologies are important.

Conclusions
This article provided a comprehensive overview of the source, chemistry, and bioactivities of 452 secondary metabolites from marine-derived Penicillium fungi described from 2021 to 2023.Although the coronavirus disease 2019 (COVID-19) pandemic limited opportunities for field collections in domestic and international travel, the numbers of new compounds from marine-derived Penicillium fungi increased abundantly, compared to 578 new compounds reported from 1991 to 2020 [6,7].This trend might be associated with fungal large-scale cultures under laboratory conditions and the significant impact of penicillin, the first broad-spectrum antibiotic in drug development [126].In addition, fungal culture methods, extraction and separation techniques, structure identification technology, and biological screening methods have reached a relatively mature level [125].
New methods and in-depth research on important compounds have been carried out.Affected by the COVID-19 pandemic, both pathways of TNF-α-induced NFκB activation and TGF-β-induced Smad activation were applied to evaluate azaphilone compounds for the first time [23].The HPLC-MS/MS analyses [9], one-pot/two-stage precursor-directed biosynthesis approach [88], and molecular networks of MS/MS data generated with Global Natural Products Social Molecular Networking (GNPS) [13] have expanded the scope of research on metabolites, especially trace components of marine-derived

Conclusions
This article provided a comprehensive overview of the source, chemistry, and bioactivities of 452 secondary metabolites from marine-derived Penicillium fungi described from 2021 to 2023.Although the coronavirus disease 2019 (COVID-19) pandemic limited opportunities for field collections in domestic and international travel, the numbers of new compounds from marine-derived Penicillium fungi increased abundantly, compared to 578 new compounds reported from 1991 to 2020 [6,7].This trend might be associated with fungal large-scale cultures under laboratory conditions and the significant impact of penicillin, the first broad-spectrum antibiotic in drug development [126].In addition, fungal culture methods, extraction and separation techniques, structure identification technology, and biological screening methods have reached a relatively mature level [125].
New methods and in-depth research on important compounds have been carried out.Affected by the COVID-19 pandemic, both pathways of TNF-α-induced NFκB activation and TGF-β-induced Smad activation were applied to evaluate azaphilone compounds for the first time [23].The HPLC-MS/MS analyses [9], one-pot/two-stage precursor-directed biosynthesis approach [88], and molecular networks of MS/MS data generated with Global Natural Products Social Molecular Networking (GNPS) [13] have expanded the scope of research on metabolites, especially trace components of marine-derived Penicillium fungi.Co-culture [66,97,100,107] and OSMAC [17,18,20,111] have been used to explore the structural diversity of secondary metabolites from the fungi.Further research on the known compounds, whether penicopeptide A as a candidate compound for osteoporosis prevention [12] or the anti-pancreatic cancer activity of dicitrinone G evaluated using a mouse model [11], provides an opportunity to diversify the targets, increasing the value of natural products from marine-derived Penicillium fungi.
In summary, marine-derived Penicillium fungi resources are found worldwide and have attracted great attention due to their diverse chemical structures.Penicillium fungi have produced a large number of structurally novel and bioactively potent compounds, such as polyketides, alkaloids and terpenoids.Over a thousand secondary metabolites from marine-derived Penicillium fungi have already been reported in the past thirty-three years .Although none of them have reached the market yet, which could partly be related to non-comprehensive screening approaches and a lack of sustained lead optimization, the mass production of trace amounts of compounds by symbiotic Penicillium fungi and the symbiotic relationship with the marine host make marine-derived Penicillium fungi a very important source of bioactive compounds for drug discovery.

3 .
Statistical Analysis of New Natural Products from Marine-Derived Penicillium

Figure 11 .
Figure 11.The proportion of the Penicillium fungi derived from different marine habitats.

Figure 12 .
Figure 12.The proportion of new bioactive compounds in each chemical class.

Figure 11 .
Figure 11.The proportion of the Penicillium fungi derived from different marine habitats.

3 .
Statistical Analysis of New Natural Products from Marine-Derived Penicillium

Figure 11 .
Figure 11.The proportion of the Penicillium fungi derived from different marine habitats.

Figure 12 .Figure 12 .
Figure 12.The proportion of new bioactive compounds in each chemical class.

Figure 13 .
Figure 13.The percentage distribution of new compounds with different bioactivities.

Figure 13 .
Figure 13.The percentage distribution of new compounds with different bioactivities.

Figure 14 .
Figure 14.(A) The proportion distribution of new compounds with different bioactivities in each chemical class; (B) the proportion distribution of new compounds with different chemical classes in each bioactivity.

Figure 14 .
Figure 14.(A) The proportion distribution of new compounds with different bioactivities in each chemical class; (B) the proportion distribution of new compounds with different chemical classes in each bioactivity.

Table 1 .
New compounds from marine-derived Penicillium fungi.