First synthesis of (+)-myrrhanol C, an anti-prostate cancer lead

Unusually cyclized triterpenoids: occurrence, biosynthesis and chemical synthesis

Covering: 2009 to 2021Biosynthetically, most of the syntheses of triterpenes follow the cascade cyclization and rearrangement of the acyclic precursors viz., squalene (S) and 2,3-oxidosqualene (OS), which lead to the very well known tetra- and pentacyclic triterpene skeletons. Aside from these, numerous other triterpenoid molecules are also reported from various natural sources and their structures are derived from "S" and "OS" via some unusual cyclization operations which are different from the usual tetra- and pentacyclic frameworks. Numerous compelling advances have been made and reported in the identification of these unusual cyclized mono-, di-, tri- and tetracyclic triterpenes between 2009 and 2021. Besides a dramatic increase in the newly isolated uncommon cyclized triterpenoids, substantial progress in the (bio)-synthesis of these triterpenes has been published along with significant progress in their biological effects. In this review, 180 new unusual cyclized triterpenoids together with their demonstrated biogenetic pathways, syntheses and biological effects will be categorized and discussed.

Two new polypodane-type bicyclic triterpenoids from mastic

Pistacia lentiscus L. is an evergreen shrub belonging to the Anacardiaceae family, cultivated exclusively in the southern area of Chios Island. Mastic gum as a unique natural resin of the tree Pistacia lentiscus L. has been used extensively in functional foods and traditional medicine. The biological properties of Pistacia resins may be influenced by different chemical constituents. Herein the present work is aimed to further explore the diverse triterpenoids of mastic, and evaluate their anti-inflammatory activity. Two undescribed polypodane-type bicyclic triterpenoids were isolated from the Pistacia resins, their structures were elucidated using ultraviolet, infrared, high resolution electrospray ionization mass spectroscopy (HRESIMS), and nuclear magnetic resonance data. LPS-stimulated RAW264.7 macrophages were incubated with various concentrations of isolated compounds, and results showed that compounds 1 and 2 inhibited nitric oxide production in LPS-induced RAW264.7 cells with IC50 values of 28.1 and 32.6 µM, respectively.

Scalable biocatalytic C-H oxyfunctionalization reactions

Catalytic C-H oxyfunctionalization reactions have garnered significant attention in recent years with their ability to streamline synthetic routes toward complex molecules. Consequently, there have been significant strides in the design and development of catalysts that enable diversification through C-H functionalization reactions. Enzymatic C-H oxygenation reactions are often complementary to small molecule based synthetic approaches, providing a powerful tool when deployable on preparative-scale. This review highlights key advances in scalable biocatalytic C-H oxyfunctionalization reactions developed within the past decade.

E-Z isomerization in Suzuki cross-couplings of haloenones: ligand effects and evidence for a separate catalytic cycle

Suzuki cross-coupling of haloalkenes is generally assumed to occur with retention of the alkene stereochemistry. While studying Suzuki cross-couplings on E-1,2-dichlorovinyl phenyl ketone, we were surprised to observe extensive isomerization. More surprisingly, the ligand employed strongly influenced the degree of isomerization: DPEphos and Xantphos led to 96% isomerized cross-coupled product whereas reactions in the absence of a phosphine ligand, or reactions employing t-BuXantphos, gave 94% retention of stereochemistry. While E-Z isomerization in Pd-catalyzed vinylic couplings has previously been attributed to events within the cross-coupling catalytic cycle, we present experimental and computational evidence for a separate Pd-catalyzed isomerization process in these reactions.

Bioinspired synthesis of pentacyclic onocerane triterpenoids

The first chemical synthesis of pentacyclic onocerane triterpenoids (+)-cupacinoxepin and (+)-onoceranoxide is described.

The first chemical synthesis of pentacyclic onocerane triterpenoids has been achieved. A putative biomimetic tricyclization cascade is employed to forge a fused decalin-/oxepane ring system. The synthetic route proceeds to (+)-cupacinoxepin in seven steps and to (+)-onoceranoxide in eight steps in the longest linear sequence, when starting from geranyl chloride and (+)-sclareolide. The bioinspired epoxypolyene cyclization is supported by computational and enzymatic studies.

Scalable Synthesis of the Amber Odorant 9-epi-Ambrox through a Biomimetic Cationic Cyclization/Nucleophilic Bromination Reaction

A novel biomimetic nucleophilic bromocyclization reaction is used in the key step of a new and straightforward synthesis of 9-epi-Ambrox, an organic compound of high interest and value in the context of fragrances. This strategic reaction allows access to 9-epi-Ambrox on a gram scale from a dienyne derivative, easily available from geraniol, following a sequence of seven steps (35% global yield) with just one purification process. Both enantiomers of the molecule were obtained by a challenging enzymatic resolution.

Synthesis and anticancer activity of novel fused pyrimidine hybrids of myrrhanone C, a bicyclic triterpene of Commiphora mukul gum resin

Myrrhanone C [8(R)-3-oxo-8-hydroxypolypoda-13E,17E,21-triene], a bicyclic triterpene isolated from the gum resin of Commiphora mukul, has been chemically transformed to synthesize a series of ten novel pyrimidine hybrids in good to excellent yields. The synthesized compounds (2-22) were evaluated for their anticancer potential against a panel of six cancer cell lines, namely A-549 (lung), Hela (cervical), MCF-7 (breast), ACHN (renal), Colo-205 (colon) and B-16 (mouse melanoma) by employing the MTT assay. In general, the synthesized compounds showed significant anticancer activity against all the cancer cell lines tested. Interestingly, the pyrimidine hybrids 18 and 19 showed good activity against the A-549, MCF-7, B-16, Colo-205 and ACHN cancer cell lines with [Formula: see text] values between 7.7-37.8 [Formula: see text]M. Most significantly, compounds 19 (IC[Formula: see text]: 7.7 [Formula: see text]M) and 18 (IC[Formula: see text]: 9.5 [Formula: see text]M) showed about five- and six-fold enhanced activities, respectively, compared to the parent myrrhanone C (1) against A-549 cell line. Flow cytometric analysis revealed that compounds 18 and 19 induced apoptosis in A-549 cells and arrested the cell growth in the G0/G1 phase.