Nonanomeric Spiroketals in Natural Products:  Structures, Sources, and Synthetic Strategies

Aho, Jatta E.; Pihko, Petri M.; Rissa, Terhi K.

doi:10.1021/cr050559n

Cited by 362 publications

(164 citation statements)

References 202 publications

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“…aq HF, [37] CSA [37] ) only afforded trace amounts of the target 58 (Scheme 9). On recommendation from a wonderful review by Pihko et al, [38] direct methods for conversion of 52 to 58 (i.e., treatment with HF·py, [39] aq HF [40] or HCl [41,42] ) were then investigated, which unfortunately provided little improvement. Following the work of Nakata, [43] however, TBS and acetonide deprotection performed with hydrogen fluoride pyridine complex afforded the polyol 59, which on treatment with CAN [44] revealed the target in 54 % yield over two steps (substituting CAN for PIFA [45] failed).…”

Section: Wwwchemeurjorgmentioning

confidence: 99%

Anticancer Agents from the Australian Tropical Rainforest: Spiroacetals EBC‐23, 24, 25, 72, 73, 75 and 76

Dong

Schill

Grange

et al. 2009

Chemistry A European J

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EBC-23, 24, 25, 72, 73, 75 and 76 were isolated from the fruit of Cinnamomum laubatii (family Lauraceae) in the Australian tropical rainforests. EBC-23 (1) was synthesized stereoselectively, in nine linear steps in 8 % overall yield, to confirm the reported relative stereochemistry and determine the absolute stereochemistry. Key to the total synthesis was a series of Tietze-Smith linchpin reactions. The novel spiroacetal structural motif, exemplified by EBC-23 (1), was found to inhibit the growth of the androgen-independent prostate tumor cell line DU145 in the mouse model, indicating potential for the treatment of refractory solid tumors in adults.

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Section: Wwwchemeurjorgmentioning

confidence: 99%

Anticancer Agents from the Australian Tropical Rainforest: Spiroacetals EBC‐23, 24, 25, 72, 73, 75 and 76

Dong

Schill

Grange

et al. 2009

Chemistry A European J

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“…The suitably protected core structure B would be assembled by a Michael addition/spiroacetalization cascade from the linear precursor C, which would itself derive from aldehyde D and methyl ketone E by an aldol condensation. [10,14,15] Much to our surprise, however, treatment of 4 as the synthetic equivalent of the envisaged cyclization precursor C with dilute HCl furnished an almost statistical mixture of the diastereomeric spiroacetal products 5-8 (Scheme 3). [10] In contrast to a previous model study by Snider,[11a] attempts to equilibrate the crude mixture by exposure to various acids were futile.…”

Section: Introductionmentioning

confidence: 99%

Total Synthesis of Berkelic Acid

Snaddon

Buchgraber

Schulthoff

et al. 2010

Chemistry A European J

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A productive total synthesis of both enantiomers of berkelic acid (1) is outlined that takes the structure revision of this bioactive fungal metabolite previously proposed by our group into account. The successful route relies on a fully optimized triple-deprotection/1,4-addition/spiroacetalization cascade reaction sequence, which delivers the tetracyclic core 32 of the target as a single isomer in excellent yield. The required cyclization precursor 31 is assembled from the polysubstituted benzaldehyde derivative 20 and methyl ketone 25 by an aldol condensation, in which the acetyl residue in 20 transforms from a passive protecting group into an active participant. Access to fragment 25 takes advantage of the Collum-Godenschwager variant of the ester enolate Claisen rearrangement, which clearly surpasses the classical Ireland-Claisen procedure in terms of diastereoselectivity. Although it is possible to elaborate 32 into the target without any additional manipulations of protecting groups, a short detour consisting in the conversion of the phenolic -OH into the corresponding TBS-ether is beneficial. It tempers the sensitivity of the compound toward oxidation and hence improves the efficiency and reliability of the final stages. Orthogonal ester groups for the benzoate and the aliphatic carboxylate terminus of the side chain secure an efficient liberation of free berkelic acid in the final step of the route.

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“…[1] Deoxyhexoses are an important class of glycans which occur widely in natural products such as antibiotics and anticancer agents. [1b, 2] Thus, it is not surprising that much research has been devoted to the development of efficient and stereoselective methodologies which can give access to this important class of chiral acetals.…”

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confidence: 99%

A 3,4‐trans‐Fused Cyclic Protecting Group Facilitates α‐Selective Catalytic Synthesis of 2‐Deoxyglycosides

et al. 2014

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A practical approach has been developed to convert glucals and rhamnals into disaccharides or glycoconjugates with high a-selectivity and yields (77-97 %) using a trans-fused cyclic 3,4-O-disiloxane protecting group and TsOH·H 2 O (1 mol %) as a catalyst. Control of the anomeric selectivity arises from conformational locking of the intermediate oxacarbenium cation. Glucals outperform rhamnals because the C6 side-chain conformation augments the selectivity.

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Nonanomeric Spiroketals in Natural Products: Structures, Sources, and Synthetic Strategies

Cited by 362 publications

References 202 publications

Anticancer Agents from the Australian Tropical Rainforest: Spiroacetals EBC‐23, 24, 25, 72, 73, 75 and 76

Anticancer Agents from the Australian Tropical Rainforest: Spiroacetals EBC‐23, 24, 25, 72, 73, 75 and 76

Total Synthesis of Berkelic Acid

A 3,4‐trans‐Fused Cyclic Protecting Group Facilitates α‐Selective Catalytic Synthesis of 2‐Deoxyglycosides

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