## 3 Chemistry and Biological Activities of Selected Meroterpenoids
Then, compound **301** was followed by regioselective deprotonation/o-methylation under lithium hydride, \(\alpha\),\(\alpha\),\(\alpha^{*}\)-tris(4-hydroxyphenyl)-1-ethyl-4-isopropylbenzene (TPPA) followed by Mel, and subsequent Simmons-Smith cyclopropanation reaction sequence generated cyclopropane **302**, which upon further proteolytic cleavage generated ketone **303**. Then, end triflate was formed to enable a Stille coupling reaction to afford compound **298**. This compound was subjected to Lewis acid treatment at low temperatures to provide intermediate **304** through an intramolecular oxy-cyclization reaction, which upon increasing of the temperature under the same Lewis acid removed the additional methoxy group to yield the natural product (+)-dysiherbol A (**179**). Alternatively, compound **298** was treated with a 2-step allylic oxidation and reduction reaction sequence, followed by Lewis acid mono deprotection and subsequent intramolecular oxy-cyclization to provide compound **305**. Finally, compound **305** was deprotected to provide natural product (+)-dysiherbol E (**183**). In parallel, as shown in Scheme 25, compound **298** was treated with _m_CPBA to undergo cationic 1,2-methyl shift and elimination reaction sequence to provide allylic alcohol **310**. The hydroxyl group geometry in **310** was inverted via a 2 step-reaction transformation. Namely, oxidation of the hydroxyl group using DMP treatment, followed by DIBAL-H reduction, which provided allylic alcohol **311**. Then, intramolecular oxy-cyclization of **311** mediated by BBr\({}_{3}\) generated cyclized ether **306**, which was oxidized with DMP to yield (+)-dysiherbol C (**181**). Reduction of this enone with DIBAL-H, followed by acid mediated dehydration reaction provided (+)-dysiherbol D (**182**). In summary, this synthetic strategy of the tetracyclic core of dysiherbols through the use of critical acid mediated ring construction sequences [90]. This unique synthetic strategy serves as the foundation to access the natural products and their derivatives. The strongylophorines meroditerpenoids have been isolated from various sources including the marine sponge _Petrosia corticata_, and they have been demonstrated to be promising proteasome inhibitors [91]. Access to these natural products to develop compound libraries is desirable. A recent streamlined total synthesis of strongylophorine-2 (STR-2, **184**) is highlighted in Scheme 26 [92]. The synthesis capitalizes on a novel iron (III)-mediated rearrangement-cyclization cascade reaction. The synthesis commenced with the esterification of natural product isocuppressic acid **312**, followed by treatment with 1,1'-(Azodicarbonyl)dipiperidine (ADDP) under Mitsunobu reaction conditions to etherify the allylic alcohol, generating compound **314**. Next, compound **314** was exposed to Lewis acid Iron trichloride, which mediated the key acid catalyzed reaction that facilitated the C-O to C-C [3,3]-Claisen rearrangement, followed by ring closure to afford compound **316** as the major product as shown in Scheme 26. Benzyl deprotection with Pd/C provided STR-1 (**184a**), and further deprotection of the methoxy group led to STR-3 (**184b**). Alternatively, **184a** could be subjected to amation conditions to yield compound **317**, which was further functionalized with lead tetraacetate (LTA) and iodine-promoted hypoiodite reaction under photolysis to provide the di-iodo compound **318**. Compound **318** was set for an intramolecular cyclization under basic conditions with elimination of the other iodo-group to provide 1,2-didehydro-STR-9 (**184c**) as the unique intermediate, which was reduced under Pd/C to provide STR-9 (**184d**). Next removal of the methoxy-protection group resulted in the natural product STR-2 (**184**) in good yields. Finally, a selected number of monoterpene indole alkaloids, which represent a large group of more than 3000 different compounds and are mainly present in three families: _Rubiaceae_, _Apcyaceae_, and _Loganiaceae_ will be included in this review.