Synthesis of acyldodecaheterocycles derived from (1R)-(–)-myrtenal and evaluation as chiral auxiliaries

Monoterpene Thiols: Synthesis and Modifications for Obtaining Biologically Active Substances

Monoterpene thiols are one of the classes of natural flavors that impart the smell of citrus fruits, grape must and wine, black currants, and guava and are used as flavoring agents in the food and perfume industries. Synthetic monoterpene thiols have found an application in asymmetric synthesis as chiral auxiliaries, derivatizing agents, and ligands for metal complex catalysis and organocatalysts. Since monoterpenes and monoterpenoids are a renewable source, there are emerging trends to use monoterpene thiols as monomers for producing new types of green polymers. Monoterpene thioderivatives are also known to possess antioxidant, anticoagulant, antifungal, and antibacterial activity. The current review covers methods for the synthesis of acyclic, mono-, and bicyclic monoterpene thiols, as well as some investigations related to their usage for the preparation of the compounds with antimicrobial properties.

Structural Features of Diacyldodecaheterocycles with Pseudo-C2-Symmetry: Promising Stereoinductors for Divergent Synthesis of Chiral Alcohols

Pseudo-C₂-symmetric dodecaheterocyclic structures, which possess two acyl/aroyl groups disposed on either a cis- or trans-relative configuration, were prepared from the naturally occurring (-)-(1R)-myrtenal. Addition of Grignard reagents (RMgX) to the diastereoisomeric mixture of these compounds unexpectedly showed that nucleophilic additions to the two prochiral carbonyl centers gave the same stereochemical result in both cis/trans diastereoisomers, making unnecessary the separation of this mixture. Noticeably, both carbonyl groups showed different reactivity because one of them is attached to an acetalic carbon and the other to a thioacetalic carbon. Furthermore, addition of RMgX to the carbonyl attached to the former carbon takes place through the re face, while addition to the second one proceeds through the si face, thus affording the corresponding carbinols in a highly diastereoselective process. This structural feature allowed the sequential hydrolysis of both carbinols, yielding separately (R)- and (S)-1,2-diols after reduction with NaBH₄. The mechanism of the asymmetric Grignard addition was explained by density functional theory calculations. This approach contributes to the development of the divergent synthesis of structurally and/or configurationally different chiral molecules.

de la Torre A, M. Muñiz F, Pertino MW, Alarcón B, Ormazabal V, Nova-Lamperti E, Zúñiga FA, Jiménez CA. Synthesis and Cytotoxic Analysis of Novel Myrtenyl Grafted Pseudo-Peptides Revealed Potential Candidates for Anticancer Therapy

Myrtenal is a natural monoterpene isolated from essential oils of several plants and their derivates have shown to have several biological properties including cytotoxicity. The cytotoxic activity of these derivates are being investigated for their antitumor effect leading to the development of potential anticancer agents. In this study, novels Myrtenyl grafted pseudo-peptides were designed, synthesized and functionally characterized as possible therapeutic agents for cancer treatment. Thirteen novel Myrtenyl grafted pseudo-peptides were prepared in high atom economy and efficiency by a classic Ugi-4CR and sequential post-modification. Their structures were confirmed by NMR, and ESI-MS, and its cytotoxic activity was evaluated in three cancer cell lines and primary CD4+ T cells at different proliferative cycles. Our results revealed that some of these compounds showed significant cytotoxicity against human gastric, breast and colon adenocarcinoma cells lines, but not against human dermal fibroblast cell line. Moreover, from the thirteen novel myrtenyl synthesized the compound (1R,5S)-N-{[1-(3-chlorophenyl)-1H-1,2,3-triazol-4-yl]methyl}-N-[2-(cyclohexylamino)-2–oxoethyl]-6,6-dimethylbicyclo[3.1.1]hept-2-ene-2-carboxamide (3b) proved to be the best candidate in terms of acceptable EC₅₀, and E_max values in cancer cell lines and at inducing cytotoxicity in CD4+ T cells undergoing active proliferation, without affecting non-proliferating T cells. Overall, the synthesis and characterization of our Myrtenyl derivates revealed novel potential anticancer candidates with selective cytotoxic activity.

Conformational, configurational, and supramolecular studies of podocephalol acetate from Lasianthaea aurea

Although podocephalol (1) and its derived acetate 2 were found in Lasianthaea podocephala four decades ago, and 1 was later detected in the essential oils of several vegetal species, its absolute configuration (AC) and conformational preferences remained to be established. The structures of ar-himachalene 1, now isolated from Lasianthaea aurea, and its derived acetate 2, were herein confirmed by extensive 1D and 2D nuclear magnetic resonance (NMR) studies, while the conformational preferences of the cycloheptene was established by density functional theory (DFT) calculations, which in combination with vibrational circular dichroism measurements provided the (R) absolute configuration of the molecules. The structure and AC were further verified through the Flack and Hooft parameters calculations derived from single crystal X-ray diffraction data of 2. In addition, careful evaluation of the crystal data allowed observing supramolecular layers cell package, an uncommon property in natural terpenes that might have potential applications. A transmission electron microscopy analysis of crystal of 2 was also possible, providing its physical characteristics at the micrometric scale.

PTSA-Catalyzed Reaction of Alkyl/Aryl Methyl Ketones with Aliphatic Alcohols in the Presence of Selenium Dioxide: A Protocol for the Generation of an α-Ketoacetals Library

A novel approach has been developed for the synthesis of a wide range of α-ketoacetals by the reaction of alkyl/aryl methyl ketones and aliphatic alcohols in the presence of selenium dioxide catalyzed by p-toluenesufonic acid. This method represents a general route to obtain a wide variety of α-ketoacetals in a simple, rapid, and practical manner. This approach is particularly attractive because of the easy availability of the starting materials, mild reaction temperature, and good yields of the products. The resulting α-ketoacetals are of much synthetic value as organic intermediates.