Isolation and total syntheses of cytotoxic cryptolactones A1, A2, B1, and B2: α,β-unsaturated δ-lactones from a Cryptomyzus sp. aphid

Mukaiyama aldol reaction: an effective asymmetric approach to access chiral natural products and their derivatives/analogues

The Mukaiyama aldol reaction is generally a Lewis-acid catalyzed cross-aldol reaction between an aldehyde or ketone and silyl enol ether. It was first described by Mukaiyama in 1973, almost 5 decades ago, to achieve the enantioselective synthesis of β-hydroxy carbonyl compounds in high percentage yields. Mukaiyama aldol adducts play a pivotal role in the synthesis of various naturally occurring and medicinally important organic compounds such as polyketides, alkaloids, macrolides, etc. This review highlights the significance of the Mukaiyama aldol reaction towards the asymmetric synthesis of a wide range of biologically active natural products reported recently (since 2020).

Substituted Isocoumarins: An Assemble of Synthetic Strategies Towards 3-Substituted and 3,4-Disubstituted Isocoumarins

The versatility of isocoumarin frameworks offers the privilege to access many pharmacological targets. This unique heterocycle core present in many natural products and complex organic molecules contribute to medicinal chemistry as anti-cancer, anti-inflammatory and immunomodulatory agents. The attractive properties exhibited by its analogues urged the scientists to explore their synthetic analogues. In regard to the myriads of synthetic methodologies, we have compiled a review update covering all the articles that have been published towards the synthesis of 3-substituted and 3,4-disubstituted isocoumarins. Additionally, we have also highlighted a systematic survey of catalytic methods for their synthesis along with their scope towards diverse functionalizations and plausible mechanistic aspects.

Synthesis of a Model Compound of the Unique Meroterpenoids Cryptolaevilactones

Cryptolaevilactones (CLs) A-L, found in the leaves and twigs of Cryptocarya laevigata, are unique natural meroterpenoids with a spiro[3.5]nonane skeleton. We report the total synthesis of a simplified model compound of CLs A-C. The synthetic route included introduction of a styryl group and coupling of a lactone moiety to a spiro ring system, which was constructed by a pinacol-like rearrangement.

Total Syntheses and Cytotoxic Evaluations of Cryptolactones A1, A2, B1, B2, and Their Derivatives

The cryptolactones A₁, A_2, B₁, and B₂ isolated from a Cryptomyzus sp. aphid were synthesized via the Mukaiyama aldol reaction and olefin metathesis. Their antipodes and derivatives were also synthesized by the same strategy to investigate structure-activity relationships. These compounds exhibited cytotoxic activity against human promyelocytic leukemia HL-60 cells with IC₅₀ values of 2.1-42 µM.

A role of uroleuconaphins, polyketide red pigments in aphid, as a chemopreventor in the host defense system against infection with entomopathogenic fungi

Four red polyketide pigments, uroleuconaphins A₁ (1) and B₁ (2) and their glucosides 3 and 4, were isolated from the red goldenrod aphid Uroleucon nigrotuberculatum. Although these red pigments exist only as glucosides 3 and 4 in the intact insect body, 3 and 4 convert instantly to aglycones 1 and 2 at death. Pigments 1 and 2 inhibited the growth of Lecanicillium sp. (Ascomycota: Cordycipitaceae) and 1, 2, and 3 were active against Conidiobolus obscurus (Entomophthoromycota; Entomophthorales); these fungal species are pathogenic. We therefore regard aphid pigments 1-4 as chemopreventive agents that aid in the resistance of infection by entomopathogenic fungi at the level of the individual aphid and/or at the species level.