An expedited approach to the vitamin D trans-hydrindane building block from the Hajos dione

Methodology for the Construction of the Bicyclo[4.3.0]nonane Core

The bicyclo[4.3.0]nonane scaffold, commonly known as a hydrindane, is a common structural motif found in many terpenoid structures and one that remains a challenge for synthetic chemists to elaborate with appropriate regio- and stereo-selectivity. Over the course of the study of terpene natural products, the elaboration of the hydrindane structure has seen progress on the utilization of both old and newer methods to achieve the desired outcomes. This review seeks to serve as a general overview of these methods, and detail specific examples.

α-Thioalkylation of Zinc Dienolates as an Entry to 4-Substituted 1-tert-Butoxy-7a-methylhexahydroindenes

Hexahydroindenes 10 are readily available in 3 steps with an overall yield of 41 – 45 % starting from the Hajos Wiechert ketone 1. Alkylation of the α,β-unsaturated ketone 1 at C-4 has been achieved by thioalkylation of the corresponding zinc dienolate 2 with α-chlorosulfides of type 3. Subsequent in situ reduction and desulfurization of the β-(phenylthio) ketones 4 leads directly to the 4-substituted hexahydroindene-5-ols 6 which can be deoxygenated via their mesylates to the hexahydroindenes 10.

Total synthesis of (+)-sieboldine a: evolution of a pinacol-terminated cyclization strategy

This article describes synthetic studies that culminated in the first total synthesis of the Lycopodium alkaloid sieboldine A. During this study, a number of pinacol-terminated cationic cyclizations were examined to form the cis-hydrindanone core of sieboldine A. Of these, a mild Au(I)-promoted 1,6-enyne cyclization that was terminated by a semipinacol rearrangement proved to be most efficient. Fashioning the unprecedented N-hydroxyazacyclononane ring embedded within the bicyclo[5.2.1]decane-N,O-acetal moiety of sieboldine A was a formidable challenge. Ultimately, the enantioselective total synthesis of (+)-sieboldine A was completed by forming this ring in good yield by cyclization of a protected-hydroxylamine thioglycoside precursor.

Synthesis and olfactory activity of unnatural, sulfated 5β-bile acid derivatives in the sea lamprey (Petromyzon marinus)

A variety of unnatural bile acid derivatives (9a-9f) was synthesized and used to examine the specificity with which the sea lamprey (Petromyzon marinus) olfactory system detects these compounds. These compounds are analogs of petromyzonol sulfate (PS, 1), a component of the sea lamprey migratory pheromone. Both the stereochemical configuration at C5 (i.e., 5α vs. 5β) and the extent and sites of oxygenation (hydroxylation or ketonization) of the bile acid derived steroid skeleton were evaluated by screening the compounds for olfactory activity using electro-olfactogram recording. 5β-Petromyzonol sulfate (9a) elicited a considerable olfactory response at sub-nanomolar concentration. In addition, less oxygenated systems (i.e., 9b-9e) elicited olfactory responses, albeit with less potency. The sea lamprey sex pheromone mimic 9f (5β-3-ketopetromyzonol sulfate) was also examined and found to produce a much lower olfactory response. Mixture studies conducted with 9a and PS (1) suggest that stimulation is occurring via similar modes of activation, demonstrating a relative lack of specificity for recognition of the allo-configuration (i.e., 5α) in sea lamprey olfaction. This attribute could facilitate design of pheromone analogs to control this invasive species.

Total synthesis of (+)-sieboldine A

The first total synthesis of (+)-sieboldine A was completed in 20 steps from readily available (3aS,6aR)-3,3a,4,6a-tetrahydro-2H-cyclopenta[b]furan-2-one (5). Key steps are as follows: (a) a pinacol-terminated 1,6-enyne cyclization reaction to form the cis-hydrindanone core (11 --> 12), (b) formation of the spiro tetrahydrofuran ring by stereoselective DMDO oxidation of tricyclic dihydropyran intermediate 15, and (c) formation of the unprecedented N-hydroxyazacyclononane ring by cyclization of a thioglycoside precursor (18 --> 19).

Expedited Approach to the Vitamin D trans-Hydrindane Building Block from the Hajos Dione. Comparative Study on Various Methods for the Selective Deoxygenation of One of the Hydroxy Groups in a Diol

1 alpha,25-Dihydroxyvitamin D3 (calcitriol, 1) is a bioregulator important for the treatment of various human metabolic diseases and biomedical research. Herein, we report an efficient diastereoselective approach to the key trans-hydrindane building block for calcitriol synthesis (2a) starting from the readily accessible optically active tetrahydroindenedione derivative (Hajos dione, 3). It was found that epoxide ring opening in a related hydroxy epoxide (7) with sodium cyanoborohydride-BF3 x Et2O occurs by hydride anion addition at the ring juncture position to produce a vicinal diol with the trans-hydrindane ring system (6a). Four methods for selective deoxygenation of the sterically less shielded hydroxy group in diol 6a were examined with an approach based on a cyclic sulfate of the diol as the most efficient and operationally convenient method.