Biomimetic Synthesis of Two Salmahyrtisanes: Salmahyrtisol A and Hippospongide A

Concertedness and Activation Energy Control by Distal Methyl Group during Ring Contraction/Expansion in Scalarane-Type Sesterterpenoid Biosynthesis

Salmahyritisol A, similan A, and hippospongide A, which are scalarane-type sesterterpenoids, feature 6/6/5/7/5 pentacyclic skeletons. Although their biosyntheses have been previously proposed to involve a unique skeletal rearrangement reaction, the detailed reaction mechanism remains unclear as none of the corresponding biosynthetic enzymes for this reaction have been reported. Herein, this skeletal rearrangement reaction was investigated using computational techniques, which revealed the following four key features: (i) the distal 24-Me substituent controls both the concertedness and activation energy of this transformation, (ii) enzymes are not responsible for the observed regioselectivity of C12-C20 bond formation, (iii) stereoselectivity is enzyme-regulated, and (iv) protonation is a key step in this skeletal rearrangement process. These new findings provide insight into the C-ring-contraction and D-ring-expansion mechanisms in scalarane-type sesterterpenoid biosyntheses.

Difluorodiazoethane as a masked acetylene equivalent in formal [3 + 2] cycloadditions with ketones to access 2,3-functionalized furans

A transition-metal-free [3+2] cycloaddition of CF2HCHN2 with β-ketones is reported, which enables the synthesis of 2,3-functionalized furans. Sequential defluorination, nucleophilic addition, and cyclization are key elemental steps of the reaction.

Sesterterpenoids: chemistry, biology, and biosynthesis

Covering: July 2012 to December 2019Over the last seven years, expanding research efforts focused on sesterterpenoids has led to the isolation, identification, and characterization of numerous structurally novel and biologically active sesterterpenoids. These newly reported sesterterpenoids provide diverse structures that often incorporate unprecedented ring systems and new carbon skeletons, as well as unusual functional group arrays. Biological activities of potential biomedical importance including suppression of cancer cell growth, inhibition of enzymatic activity, and modulation of receptor signaling, as well as ecologically important functions such as antimicrobial effects and deterrence of herbivorous insects have been associated with a variety of sesterterpenoids. There has also been a rapid growth in our knowledge of the genomics, enzymology, and specific pathways associated with sesterterpene biosynthesis. This has opened up new opportunities for future sesterterpene discovery and diversification through the expression of new cryptic metabolites and the engineered manipulation of associated biosynthetic machinery and processes. In this paper we reviewed 498 new sesterterpenoids, including their structures, source organisms, country of origin, relevant bioactivities, and biosynthesis.

Cytotoxic Scalarane Sesterterpenes from the Sponge Hyrtios erectus

Twelve new sesterterpenes along with eight known sesterterpenes were isolated from the marine sponge Hyrtios erectus collected off the coast of Chuuk Island, the Federated State of Micronesia. Based upon a combination of spectroscopic and computational analyses, these compounds were determined to be eight glycine-bearing scalaranes (1–8), a 3-keto scalarane (9), two oxidized-furan-bearing scalaranes (10 and 11), and a salmahyrtisane (12). Several of these compounds exhibited weak antiproliferation against diverse cancer cell lines as well as moderate anti-angiogenesis activities. The antiproliferative activity of new compound 4 was found to be associated with G0/G1 arrest in the cell cycle.

Total synthesis of sesterterpenoids

Total syntheses of biologically and structurally fascinating sesterterpenoids published between Jan. 2012 and Jan. 2018 are summarized and discussed here.

Marine natural products

Covering: 2015. Previous review: Nat. Prod. Rep., 2016, 33, 382-431This review covers the literature published in 2015 for marine natural products (MNPs), with 1220 citations (792 for the period January to December 2015) referring to compounds isolated from marine microorganisms and phytoplankton, green, brown and red algae, sponges, cnidarians, bryozoans, molluscs, tunicates, echinoderms, mangroves and other intertidal plants and microorganisms. The emphasis is on new compounds (1340 in 429 papers for 2015), together with the relevant biological activities, source organisms and country of origin. Reviews, biosynthetic studies, first syntheses, and syntheses that lead to the revision of structures or stereochemistries, have been included.

Diterpenoids of terrestrial origin

This review covers the isolation and chemistry of diterpenoids from terrestrial as opposed to marine sources and includes labdanes, clerodanes, pimaranes, abietanes, kauranes, cembranes and their cyclization products. The literature from January to December, 2015 is reviewed.