Total Synthesis of Natural Hyacinthacine C5 and Six Related Hyacinthacine C5 Epimers

The Petasis Reaction: Applications and Organic Synthesis-A Comprehensive Review

The Petasis reaction has introduced significant advancements through the use of various catalysts, solvents, methodologies, and substrates in diverse areas of chemistry, including medicinal, organic, combinatorial, biochemical, and heterocyclic chemistry. It is a prominent method for synthesizing compounds such as α-amino acids, β-amino alcohols, Aza-beta-lactams, alkylaminophenols, α-arylglycines, 2H-chromenes, aminophenols, and hydrazide alcohols. With the increasing demand for medicines, drugs, industrial products, insecticides, and pesticides, the Petasis reaction has become an indispensable and versatile tool. This review explores the range of reaction components, key mechanisms, and reaction conditions associated with the Petasis reaction. Additionally, the paper delves into the potential future directions of this reaction and highlights its various applications.

Naming of new natural products: Standard, pitfalls and tips-and-tricks

Naming a newly discovered natural product (NP) is a pleasant but difficult exercise. In most cases, the NP name will be given with reference to the species of origin, be it a plant, a marine organism, a mammalian or microbial species. For a long time, the use of biologically-based trivial names has been recommended to identify the parental linkage between the product and the originating genus or species. But the recommendation is not always followed and a multiplicity of trivial names have been attributed to NP, based on locations (country, region, city), foods, music, animals, forenames, etc. Tips-and-tricks associated with the naming of NP are underlined here. Usually, NP are differentiated across a homogeneous chemical series with a letter (from the Latin or Greek alphabet), followed or not with a number. In other cases, the change of a single letter distinguishes a series of NP. Common pitfalls associated with the naming of NP are enumerated, including the complexity of names, use of synonyms, duplicated names, confusing names and inappropriate terminology. The difficulties regularly encountered with the naming of NP are discussed. Four essential recommendations are recalled: (i) a thorough analysis of the existing products to avoid duplicated names and confusion, (ii) the use of a biologically-based trivial name to retrace the origin of the product, (iii) the strict adherence to the codes of chemical nomenclature, and (iv) the preference for simple names to facilitate transmission. Naming a new NP is a rewarding task, which shall be performed with all due skill, care and diligence.

Diastereo- and regioselective petasis aryl and allyl boration of ninhydrins towards synthesis of functionalized indene-diones and dihydrobenzoindeno-oxazin-ones

Petasis aryl and allyl borations were accomplished using substituted ninhydrins, boronic acids or 2-allyl-4,4,5,5-tetramethyl-1,3,2-dioxaborolane and 1,2-aminophenols in Hexafluoroisopropanol (HFIP) without any catalysts to synthesize different aryl and allyl derivatives of ninhydrins. The nature of substitution in the boronic acids and 1,2-amino phenols was the key factor in determining the diastereo-regioselectivity and the type of product distributions. The products were isolated and characterized by HMBC, HSQC, ¹H, ¹³C NMR experiments and X-ray single crystallographic analysis. A probable reaction pathway involves in situ formation of acyclic and cyclic ninhydrin-amino alcohol adducts, with the positioned hydroxyl group determining the stereo-regioselective outcome via tetracoordinated boron intermediates. A metal free diastereo- and regioselective Petasis aryl and allyl boration of ninhydrins.

Synthesis and Structural Revision of Glyphaeaside C

The iminosugar core of natural glyphaeaside C, originally assigned as a derivative of the piperidine natural product 1-deoxynojirimycin (DNJ), has been revised as a derivative of 2,5-dideoxy-2,5-imino-l-mannitol (l-DMDP) by the total synthesis of its enantiomer. This revised l-DMDP-derived configuration is the first of its kind to be observed in nature. The prepared iminosugars displayed the nanomolar inhibition of bovine liver β-glucosidase and β-galactosidase.

Reactivity and Synthetic Applications of Multicomponent Petasis Reactions

The Petasis boron-Mannich reaction, simply referred to as the Petasis reaction, is a powerful multicomponent coupling reaction of a boronic acid, an amine, and a carbonyl derivative. Highly functionalized amines with multiple stereogenic centers can be efficiently accessed via the Petasis reaction with high levels of both diastereoselectivity and enantioselectivity. By drawing attention to examples reported in the past 8 years, this Review demonstrates the breadth of the reactivity and synthetic applications of Petasis reactions in several frontiers: the expansion of the substrate scope in the classic three-component process; nonclassic Petasis reactions with additional components; Petasis-type reactions with noncanonical substrates, mechanism, and products; new asymmetric versions assisted by chiral catalysts; combinations with a secondary or tertiary transformation in a cascade- or sequence-specific manner to access structurally complex, natural-product-like heterocycles; and the synthesis of polyhydroxy alkaloids and biologically interesting molecules.

Corrected Structure of Natural Hyacinthacine C1 via Total Synthesis

Hyacinthacines C₁ and C₄ are natural products that were isolated from Hyacinthoides non-scripta and Scilla socialis in 1999 and 2007, respectively. Despite their different ¹H NMR and ¹³C NMR spectroscopic data, these compounds have been assigned the same structures, including absolute configurations. This work details the total synthesis of natural (+)-hyacinthacine C₁, whose structure is confirmed as being the C-6 epimer of that reported. The synthetic strategy focused on inverting the configuration at C-1 of the final hyacinthacines via operating the inversion at the corresponding carbon atom in three previously synthesized intermediates. To do this, the advanced intermediates were subjected to Swern oxidation, followed by a stereoselective reduction with L-Selectride. This approach led to the synthesis of (+)-5 -epi-hyacinthacine C₁ (15), the corrected structure for (+)-hyacinthacine C₁ (19), (+)-6,7-di- epi-hyacinthacine C₁ (23), and (+)-7- epi-hyacinthacine C₁ (29). Glycosidase inhibition assays revealed that (+)-hyacinthacine C₁ (19) proved the most active, with IC₅₀ values of 33.7, 55.5, and 78.2 μM, against the α-glucosidase of rice, human lysosome, and rat intestinal maltase, respectively.

The History of the Glycosidase Inhibiting Hyacinthacine C-type Alkaloids: From Discovery to Synthesis

BACKGROUND

The inherent glycosidase inhibitory activity and potentially therapeutic value of the polyhydroxylated pyrrolizidine alkaloids containing a hydroxymethyl substituent at the C-3 position have been well documented. Belonging to this class, the naturally occurring hyacinthacine C-type alkaloids are of general interest among iminosugar researchers. Their selective micromolar α -glycosidase inhibitory ranges (10 - 100 μM) suggest that these azasugars are potential leads for treating type II diabetes. However, the structures of hyacinthacine C1, C3 and C4 are insecure with hyacinthacine C5 being recently corrected.

OBJECTIVE

This review presents the hyacinthacine C-type alkaloids: their first discovery to the most recent advancements on the structures, biological activities and total synthesis.

CONCLUSION

The hyacinthacine C-type alkaloids are of exponentially increasing interest and will undoubtedly continue to be reported as synthetic targets. They represent a challenging but rewarding synthetic feat for the community of those interested in accessing biologically active iminosugars. Since 2009, ten total syntheses have been employed towards accessing similarly related products but only three have assessed the glycosidase inhibitory activity of the final products. This suggests the need for an accessible and universal glycosidase inhibitory assay so to accurately determine the structure-activity relationship of how the hyacinthacine C-type alkaloids inhibit specific glycosidases. Confirming the correct structures of the hyacinthacine C-type alkaloids as well as accessing various analogues continues to strengthen the foundation towards a marketable treatment for type II diabetes and other glycosidase related illnesses.