Total Synthesis of the Hamigerans

Abstract

The first total synthesis of hamigerans D, G, L, and N-Q has been accomplished. Aconvergent approachwas used to build the basic tricarbocyclic ring system bearing a5 -6-6 structure.Asequence of oxidative cleavage,homologation, and ring regeneration provided access to the 5-7-6 skeleton of hamigeran G. Based on the biogenetic hypothesis,elegant and highly efficient biomimetic transformations of hamigeran G into hamigerans D, N-Q, and Lw ere achieved. Scheme 4. Total synthesis of 6.X-ray structures are shown. Thermal ellipsoidss hown at 50 %probability. [24] DMP = Dess-Martin periodinane, NMO = 4-methyl-morpholin-4-oxide, PTSA = p-toluenesulfonic acid, Py = pyridine.Scheme 5. Biomimetic transformation of 6 into 8 and its 18-epi isomer.

Enantioselective Intramolecular ortho Photocycloaddition Reactions of 2‐Acetonaphthones

“…Two exemplary reaction were performed on compound 5 a to demonstrate the synthetic utility of the photocycloaddition products (Scheme 5). Dihydroxylation with stoichiometric quantities of N ‐methylmorpholine N ‐oxide (NMO) gave diol 8 in 47 % yield as a single diastereomer [21] . The front face of the olefin is exposed to the attack of the reagent while the acetyl group and the tetrahydrofuran ring block the back face.…”

Bioactive natural products from marine sponges belonging to family Hymedesmiidae

“…It was found that gukulenin A inhibited tumor growth in A2780-bearing mice as well as, it displayed potent cytotoxic activity against the four ovarian cancer cell lines with IC 50 values of 0.03-0.36 mM. 24 On the other hand, sesterterpenoids are also represented as small category of phorbaketal compounds and were isolated from Phorbas sp., including phorbaketals A-C (42-44), 25 phorbaketal derivative (45), 26 phorbaketals L (46) and N (47) (Fig. 8).…”

“…41 The main nucleus was proposed to be hamigerane which is a six membered nucleus (B ring) or as isohamigerane with seven membered nucleus (B ring) in the main skeleton. In case of hamigeran F additional ring exists; it resulted in formation of third skeleton named neo-hamigeran, whereas cleavage of ring B of the tricylic system leads to formation of 5-6 structure (A-C rings) which is the main skeleton of hamigeran L. 46 Moreover, the biogenetic origin of nitrogenous hamigerans is attributed to an amino acid source and hamigeran G is a precursor of the main skeleton of these nitrogenous compounds so, condensation of hamigeran G with different amino acids resulted in formation of different nitrogenous hamigerans (hamigerans D, M, N, O, P and Q). 45,46 Two new sesterterpenoidal compounds had been isolated from marine sponge Hamigera sp.…”

Progress toward the Total Synthesis of Gukulenin A: Photochemically Triggered Two-Carbon Ring Expansion Key to α-Tropolonic Ether Synthesis

“…The ex-chiral-pool synthesis of the A ring building block (+)- 20 commenced with the LAH reduction of (−)-piperitone ( 6 ) to piperitol and subsequent Prileschajew epoxidation to deliver the epoxy alcohol 9 as a single diastereomer in 49% yield (5.4 g isolated mass) after separation of the minor diastereomer by chromatography (Scheme ). Subsequent silyl ether formation produced the oxirane 10 in 89% yield (21.6 g) and set the stage for a successful Brønsted acid mediated ring-contracting Meinwald rearrangement. , Exposure of the oxirane 10 to Amberlyst-15 in CH 2 Cl 2 at room temperature afforded the corresponding cyclopentane carbaldehyde that is susceptible to oxidation in air. To limit oxidative degradation, the crude aldehyde was immediately subjected to Wittig methylenation to provide the vinylcyclopentanoid 11 as a single diastereomer in 51% yield (15.4 g) from 10 .…”