Spongipyran Synthetic Studies. Evolution of a Scalable Total Synthesis of (+)-Spongistatin 1

Four-Step Synthesis of (-)-4-epi-Presilphiperfolan-8α-ol by Intramolecular Iron Hydride Atom Transfer-Mediated Ketone-Alkene Coupling and Studies to Access trans-Hydrindanols with a Botryane Scaffold

From an (R)-(+)-pulegone-derived building block that incorporates the stereo-defined tertiary carbon bearing a methyl group, as found in the targeted sesquiterpenoid, a four-step synthesis of (-)-4-epi-presilphiperfolan-8-α-ol was achieved. The key processes involved are a ring-closing metathesis leading to a bridged alkene-tethered ketone and its subsequent Fe^III -mediated metal-hydride atom transfer (MHAT) transannular cyclization. This synthetic method, implying an irreversible addition of a carbon-centered radical upon a ketone by means of a hydrogen atom transfer upon the alkoxy radical intermediate, was also applied in the synthesis of trans-fused hydrindanols structurally related to botrydial compounds.

Naturally Occurring Organohalogen Compounds-A Comprehensive Review

The present volume is the third in a trilogy that documents naturally occurring organohalogen compounds, bringing the total number-from fewer than 25 in 1968-to approximately 8000 compounds to date. Nearly all of these natural products contain chlorine or bromine, with a few containing iodine and, fewer still, fluorine. Produced by ubiquitous marine (algae, sponges, corals, bryozoa, nudibranchs, fungi, bacteria) and terrestrial organisms (plants, fungi, bacteria, insects, higher animals) and universal abiotic processes (volcanos, forest fires, geothermal events), organohalogens pervade the global ecosystem. Newly identified extraterrestrial sources are also documented. In addition to chemical structures, biological activity, biohalogenation, biodegradation, natural function, and future outlook are presented.

The interaction of spongistatin 1 with tubulin

A tritiated derivative of the sponge-derived natural product spongistatin 1 was prepared, and its interactions with tubulin were examined. [3H]Spongistatin 1 was found to bind rapidly to tubulin at a single site (the low specific activity of the [3H]spongistatin 1, 0.75 Ci/mmol, prevented our defining an association rate), and the inability of spongistatin 1 to cause an aberrant assembly reaction was confirmed. Spongistatin 1 bound to tubulin very tightly, and we could detect no significant dissociation reaction from tubulin. The tubulin-[3H]spongistatin 1 complex did dissociate in 8 M urea, so there was no evidence for covalent bond formation. Apparent KD values were obtained by Scatchard analysis of binding data and by Hummel-Dreyer chromatography (3.5 and 1.1 μM, respectively). The effects of a large cohort of vinca domain drugs on the binding of [3H]spongistatin 1 to tubulin were evaluated. Compounds that did not cause aberrant assembly reactions (halichondrin B, eribulin, maytansine, and rhizoxin) caused little inhibition of [3H]spongistatin 1 binding. Little inhibition also occurred with the peptides dolastatin 15, its active pentapeptide derivative, vitilevuamide, or diazonamide A, nor with the vinca alkaloid vinblastine. Strong inhibition was observed with dolastatin 10, hemiasterlin, and cryptophycin 1, all of which cause aberrant assembly reactions that might actually mask the spongistatin 1 binding site. Spongistatin 5 was found to be a competitive inhibitor of [3H]spongistatin 1 binding, with an apparent Ki of 2.2 μM. We propose that the strong picomolar cytotoxicity of spongistatin 1 probably derives from its extremely tight binding to tubulin.

Conquering peaks and illuminating depths: developing stereocontrolled organic reactions to unlock nature's macrolide treasure trove

The structural complexity and biological importance of macrolide natural products has inspired the development of innovative strategies for their chemical synthesis. With their dense stereochemical content, high level of oxygenation and macrocyclic cores, we viewed the efficient total synthesis of these valuable compounds as an aspirational driver towards developing robust methods and strategies for their construction. Starting out from the initial development of our versatile asymmetric aldol methodology, this personal perspective reflects on an adventurous journey, with all its trials, tribulations and serendipitous discoveries, across the total synthesis, in our group, of a representative selection of six macrolide natural products of marine and terrestrial origin - swinholide A, spongistatin 1, spirastrellolide A, leiodermatolide, chivosazole F and actinoallolide A.

Total Synthesis of Tiacumicin B: Study of the Challenging β-Selective Glycosylations*

We give a full account of the total synthesis of tiacumicin B (Tcn-B), a natural glycosylated macrolide with remarkable antibiotic properties. Our strategy is based on our experience with the synthesis of the tiacumicin B aglycone and on unique 1,2-cis-glycosylation steps. We used sulfoxide anomeric leaving-groups in combination with a remote 3-O-picoloyl group on the donors that allowed highly β-selective rhamnosylation and noviosylation that rely on H-bond-mediated aglycone delivery. The rhamnosylated C1-C3 fragment was anchored to the C4-C19 aglycone fragment by a Suzuki-Miyaura cross-coupling. Ring-size-selective Shiina macrolactonization provided a semiglycosylated aglycone that was engaged directly in the noviolysation step with a virtually total β-selectivity. Finally, a novel deprotection method was devised for the removal of a 2-naphthylmethyl ether on a phenol, and efficient removal of all the protecting groups provided synthetic tiacumicin B.

Ring-Closing Metathesis Approaches towards the Total Synthesis of Rhizoxins

Efforts are described towards the total synthesis of the bacterial macrolide rhizoxin F, which is a potent tubulin assembly and cancer cell growth inhibitor. A significant amount of work was expanded on the construction of the rhizoxin core macrocycle by ring-closing olefin metathesis (RCM) between C(9) and C(10), either directly or by using relay substrates, but in no case was ring-closure achieved. Macrocycle formation was possible by ring-closing alkyne metathesis (RCAM) at the C(9)/C(10) site. The requisite diyne was obtained from advanced intermediates that had been prepared as part of the synthesis of the RCM substrates. While the direct conversion of the triple bond formed in the ring-closing step into the C(9)-C(10) E double bond of the rhizoxin macrocycle proved to be elusive, the corresponding Z isomer was accessible with high selectivity by reductive decomplexation of the biscobalt hexacarbonyl complex of the triple bond with ethylpiperidinium hypophosphite. Radical-induced double bond isomerization, full elaboration of the C(15) side chain, and directed epoxidation of the C(11)-C(12) double bond completed the total synthesis of rhizoxin F.

Total Synthesis of Tiacumicin B: Implementing Hydrogen Bond Directed Acceptor Delivery for Highly Selective β-Glycosylations

A total synthesis of tiacumicin B, a natural macrolide whose remarkable antibiotic properties are used to treat severe intestinal infections, is reported. The strategy is in part based on the prior synthesis of the tiacumicin B aglycone, and on the decisive use of sulfoxides as anomeric leaving groups in hydrogen-bond-mediated aglycone delivery (HAD). This new HAD variant permitted highly β-selective rhamnosylation and noviosylation. To increase convergence, the rhamnosylated C1-C3 fragment thus obtained was anchored to the C4-C19 aglycone fragment by adapting the Suzuki-Miyaura cross-coupling used for the aglycone synthesis. Ring-size-selective macrolactonization provided a compound engaged directly in the noviolysation step with virtually total β selectivity. The final efficient removal of all the protecting groups provided synthetic tiacumicin B.

Natural Products in the "Marketplace": Interfacing Synthesis and Biology

Drugs are discovered through the biological screening of collections of compounds, followed by optimization toward functional end points. The properties of screening collections are often balanced between diversity, physicochemical favorability, intrinsic complexity, and synthetic tractability (Huggins, D. J.; et al. ACS Chem. Biol. 2011, 6, 208; DOI: 10.1021/cb100420r ). Whereas natural product (NP) collections excel in the first three attributes, NPs suffer a disadvantage on the last point. Academic total synthesis research has worked to solve this problem by devising syntheses of NP leads, diversifying late-stage intermediates, or derivatizing the NP target. This work has led to the discovery of reaction mechanisms, the invention of new methods, and the development of FDA-approved drugs. Few drugs, however, are themselves NPs; instead, NP analogues predominate. Here we highlight past examples of NP analogue development and successful NP-derived drugs. More recently, chemists have explored how NP analogues alter the retrosynthetic analysis of complex scaffolds, merging structural design and synthetic design. This strategy maintains the intrinsic complexity of the NP but can alter the physicochemical properties of the scaffold, like core instability that renders the NP a poor chemotype. Focused libraries based on these syntheses may exclude the NP but maintain the molecular properties that distinguish NP space from synthetic space (Stratton, C. F.; et al. Bioorg. Med. Chem. Lett. 2015, 25, 4802; DOI: 10.1016/j.bmcl.2015.07.014 ), properties that have statistical advantages in clinical progression (Luker, T.; et al. Bioorg. Med. Chem. Lett. 2011, 21, 5673, DOI: 10.1016/j.bmcl.2011.07.074 ; Ritchie, T. J.; Macdonald, S. J. F. Drug Discovery Today 2009, 14, 1011, DOI: 10.1016/j.drudis.2009.07.014 ). Research that expedites synthetic access to NP motifs can prevent homogeneity of chemical matter available for lead discovery. Easily accessed, focused libraries of NP scaffolds can fill empty but active gaps in screening sets and expand the molecular diversity of synthetic collections.

Design and 22-step synthesis of highly potent D-ring modified and linker-equipped analogs of spongistatin 1

Spongistatin 1 is among the most potent anti-proliferative agents ever discovered rendering it an attractive candidate for development as a payload for antibody-drug conjugates and other targeted delivery approaches. Unfortunately, it is unavailable from natural sources and its size and complex stereostructure render chemical synthesis highly time- and resource-intensive. As a result, the design and synthesis of more acid-stable and linker functional group-equipped analogs that retain the low picomolar potency of the parent natural product requires more efficient and step-economical synthetic access. Using uniquely enabling direct complex fragment coupling crotyl- and alkallylsilylation reactions, we report a 22-step synthesis of a rationally designed D-ring modified analog of spongistatin 1 that is characterized by GI50 values in the low picomolar range, and a proof-of-concept result that the C(15) acetate may be replaced with linker functional group-bearing esters with only minimal reductions in potency.

Synthetic Access to the Mandelalide Family of Macrolides: Development of an Anion Relay Chemistry Strategy

The mandelalides comprise a family of structurally complex marine macrolides that display significant cytotoxicity against several human cancer cell lines. Presented here is a full account on the development of an Anion Relay Chemistry (ARC) strategy for the total synthesis of (-)-mandelalides A and L, the two most potent members of the mandelalide family. The design and implementation of a three-component type II ARC/cross-coupling protocol and a four-component type I ARC union permits rapid access respectively to the key tetrahydrofuran and tetrahydropyran structural motifs of these natural products. Other highlights of the synthesis include an osmium-catalyzed oxidative cyclization of an allylic 1,3-diol, a mild Yamaguchi esterification to unite the northern and southern hemispheres, and a late-stage Heck macrocyclization. Synthetic mandelalides A and L displayed potent cytotoxicity against human HeLa cervical cancer cells (EC50, 1.3 and 3.1 nM, respectively). This synthetic approach also provides access to several highly potent non-natural mandelalide analogs, including a biotin-tagged mandelalide probe for future biological investigation.

Marine Invertebrate Natural Products that Target Microtubules

Marine natural products as secondary metabolites are a potential major source of new drugs for treating disease. In some cases, cytotoxic marine metabolites target the microtubules of the eukaryote cytoskeleton for reasons that will be discussed. This review covers the microtubule-targeting agents reported from sponges, corals, tunicates, and molluscs and the evidence that many of these secondary metabolites are produced by bacterial symbionts. The review finishes by discussing the directions for future development and production of clinically relevant amounts of these natural products and their analogues through aquaculture, chemical synthesis, and biosynthesis by bacterial symbionts.

Marine Invertebrate Metabolites with Anticancer Activities: Solutions to the "Supply Problem"

Marine invertebrates provide a rich source of metabolites with anticancer activities and several marine-derived agents have been approved for the treatment of cancer. However, the limited supply of promising anticancer metabolites from their natural sources is a major hurdle to their preclinical and clinical development. Thus, the lack of a sustainable large-scale supply has been an important challenge facing chemists and biologists involved in marine-based drug discovery. In the current review we describe the main strategies aimed to overcome the supply problem. These include: marine invertebrate aquaculture, invertebrate and symbiont cell culture, culture-independent strategies, total chemical synthesis, semi-synthesis, and a number of hybrid strategies. We provide examples illustrating the application of these strategies for the supply of marine invertebrate-derived anticancer agents. Finally, we encourage the scientific community to develop scalable methods to obtain selected metabolites, which in the authors' opinion should be pursued due to their most promising anticancer activities.

Conformation-activity relationships of polyketide natural products

Polyketides represent an important class of secondary metabolites that interact with biological targets connected to a variety of disease-associated pathways. Remarkably, nature's assembly lines, polyketide synthases, manufacture these privileged structures through a combinatorial mixture of just a few structural units. This review highlights the role of these structural elements in shaping a polyketide's conformational preferences, the use of computer-based molecular modeling and solution NMR studies in the identification of low-energy conformers, and the importance of conformational analogues in probing the bound conformation. In particular, this review covers several examples wherein conformational analysis complements classic structure-activity relationships in the design of biologically active natural product analogues.

Exploiting pseudo C2-symmetry for an efficient synthesis of the F-ring of the spongistatins

A concise and efficient synthesis of the F-ring fragment of the potent antimitotic marine macrolide spongistatin 1 has been developed. The key sequence involves double cross-metathesis/Sharpless asymmetric dihydroxylation reactions to establish four stereocenters in a pseudo C2-symmetric array, followed by a selective protection reaction that breaks the pseudosymmetry, establishes a fifth stereocenter, and effectively differentiates the ester termini. Overall, the six contiguous stereocenters in the C(37)-C(45) F-ring fragment are established in just seven steps.

A reductive coupling strategy towards ripostatin A

Synthetic studies on the antibiotic natural product ripostatin A have been carried out with the aim to construct the C9-C10 bond by a nickel(0)-catalyzed coupling reaction of an enyne and an epoxide, followed by rearrangement of the resulting dienylcyclopropane intermediate to afford the skipped 1,4,7-triene. A cyclopropyl enyne fragment corresponding to C1-C9 has been synthesized in high yield and demonstrated to be a competent substrate for the nickel(0)-catalyzed coupling with a model epoxide. Several synthetic approaches toward the C10-C26 epoxide have been pursued. The C13 stereocenter can be set by allylation and reductive decyanation of a cyanohydrin acetonide. A mild, fluoride-promoted decarboxylation enables construction of the C15-C16 bond by an aldol reaction. The product of this transformation is of the correct oxidation state and potentially three steps removed from the targeted epoxide fragment.

DFT study on the mechanism and stereochemistry of the Petasis-Ferrier rearrangements

The Petasis-Ferrier rearrangement is a very important and useful reaction for the synthesis of multifunctional tetrahydrofurans and tetrahydropyrans from easily synthesized enol acetals. Here we report our DFT investigation of the detailed reaction mechanism of the Petasis-Ferrier rearrangement, proposing that the active promoting species in this reaction is the cationic aluminum species, instead of the usually considered neutral Lewis acid (this will give very high activation energies and cannot explain why the Petasis-Ferrier rearrangements usually take place at low temperature or under mild conditions). Calculations indicated that the mechanisms of the Petasis-Ferrier rearrangements for the formations of five- and six-membered rings are different. Formation of five-membered tetrahydrofuranone is stepwise with C-O bond cleavage to generate an oxocarbenium enolate intermediate, which then undergoes an aldol-type reaction to give the desired cyclized oxacycle. In contrast, the formation of six-membered tetrahydropyranone is a concerted and asynchronous process with the C-O bond breakage and aldol-type C-C bond formation occurring simultaneously. A DFT understanding of why the catalytic versions of the Petasis-Ferrier rearrangements cannot be realized when using R2Al(+) as the active promoting species has also been discussed. In addition, DFT calculations were used to reveal the origins of the stereochemistry observed in the Petasis-Ferrier rearrangements.

Toward a more step-economical and scalable synthesis of spongistatin 1 to facilitate cancer drug development efforts

An efficient, step-economical, and scalable synthesis of a diene-bearing AB spiroketal fragment of spongistatin 1, and a demonstration of its efficient coupling to an aldehyde derived from silylformylation of a homopropargyl alcohol to produce the entire complex C(13)-C(17) linker region are described. The scalability of the synthesis of the AB spiroketal fragment was demonstrated by the preparation of 34.5 grams by one chemist in ~60 workdays, and more than 40 grams overall. With this material in hand and having established a method for its efficient coupling to the CD fragment, we have set the stage for the rapid synthesis and evaluation of a series of analogs of the CD spiroketal.

A survey of marine natural compounds and their derivatives with anti-cancer activity reported in 2011

Cancer continues to be a major public health problem despite the efforts that have been made in the search for novel drugs and treatments. The current sources sought for the discovery of new molecules are plants, animals and minerals. During the past decade, the search for anticancer agents of marine origin to fight chemo-resistance has increased greatly. Each year, several novel anticancer molecules are isolated from marine organisms and represent a renewed hope for cancer therapy. The study of structure-function relationships has allowed synthesis of analogues with increased efficacy and less toxicity. In this report, we aim to review 42 compounds of marine origin and their derivatives that were published in 2011 as promising anticancer compounds.

Natural products: a continuing source of novel drug leads

BACKGROUND

Nature has been a source of medicinal products for millennia, with many useful drugs developed from plant sources. Following discovery of the penicillins, drug discovery from microbial sources occurred and diving techniques in the 1970s opened the seas. Combinatorial chemistry (late 1980s), shifted the focus of drug discovery efforts from Nature to the laboratory bench.

SCOPE OF REVIEW

This review traces natural products drug discovery, outlining important drugs from natural sources that revolutionized treatment of serious diseases. It is clear Nature will continue to be a major source of new structural leads, and effective drug development depends on multidisciplinary collaborations.

MAJOR CONCLUSIONS

The explosion of genetic information led not only to novel screens, but the genetic techniques permitted the implementation of combinatorial biosynthetic technology and genome mining. The knowledge gained has allowed unknown molecules to be identified. These novel bioactive structures can be optimized by using combinatorial chemistry generating new drug candidates for many diseases.

GENERAL SIGNIFICANCE

The advent of genetic techniques that permitted the isolation / expression of biosynthetic cassettes from microbes may well be the new frontier for natural products lead discovery. It is now apparent that biodiversity may be much greater in those organisms. The numbers of potential species involved in the microbial world are many orders of magnitude greater than those of plants and multi-celled animals. Coupling these numbers to the number of currently unexpressed biosynthetic clusters now identified (>10 per species) the potential of microbial diversity remains essentially untapped.

Complex fragment coupling by crotylation: A powerful tool for polyketide natural product synthesis

The first examples of the use of crotylation as a stereocontrolled complex fragment coupling strategy are described. Asymmetric aldehyde isoprenylation provides access to 2-substituted-1,3-butadienes that may be subjected to highly regio- and stereoselective 1,4 hydrosilylation with trichlorosilane. After complexation with a chiral diamine, the 2-sub-stituted-cis-crotylsilanes may be employed in highly diastereoselective Sc(OTf)3-catalyzed aldehdye crotylation reactions.

Design, synthesis, and biological evaluation of diminutive forms of (+)-spongistatin 1: lessons learned

The design, synthesis, and biological evaluation of two diminutive forms of (+)-spongistatin 1, in conjunction with the development of a potentially general design strategy to simplify highly flexible macrocyclic molecules while maintaining biological activity, have been achieved. Examination of the solution conformations of (+)-spongistatin 1 revealed a common conformational preference along the western perimeter comprising the ABEF rings. Exploiting the hypothesis that the small-molecule recognition/binding domains are likely to comprise the conformationally less mobile portions of a ligand led to the design of analogues, incorporating tethers (blue) in place of the CD and the ABCD components of the (+)-spongistatin 1 macrolide, such that the conformation of the retained (+)-spongistatin 1 skeleton would mimic the assigned solution conformations of the natural product. The observed nanomolar cytotoxicity and microtubule destabilizing activity of the ABEF analogue provide support for both the assigned solution conformation of (+)-spongistatin 1 and the validity of the design strategy.

In vitro and in vivo anticancer activity of (+)-spongistatin 1

The marine natural product (+)-spongistatin 1 is an extremely potent growth inhibitory agent having activity against a wide variety of cancer cell lines, while exhibiting low cytotoxicity against quiescent human fibroblasts. Consistent with a microtubule-targeting mechanism of action, (+)-spongistatin 1 causes mitotic arrest in DU145 human prostate cancer cells. More importantly, (+)-spongistatin 1 exhibits significant in vivo antitumor activity in the LOX-IMVI human melanoma xenograft model. (+)-Spongistatin 1 is, thus, an important class of microtubule targeting anticancer agent that warrants further investigation.

Phorboxazole Synthetic Studies: Design, Synthesis and Biological Evaluation of Phorboxazole A and Hemi-Phorboxazole A Related Analogues

The design, synthesis and biological evaluation of a new phorboxazole analogue, comprising an acetal replacement for the C-ring tetrahdropyran of the natural product and carrying a potency-enhancing C(45-46) vinyl chloride side chain, is described. In addition, the synthesis of (+)-hemi-phorboxazole A and a series of related hemi-phorboxazole A analogues has been achieved. The new acetal ring replacement analogue displayed activity comparable to that of the parent natural product against HCT-116 (colon) cells (IC(50) 2.25 ng/mL). Equally important, the phorboxazole analogue and two related hemiphorboxazole A congeners exhibited significant antifungal activity when assayed against pathogenic Candida albicans strains.

Interactions of halichondrin B and eribulin with tubulin

Compounds that modulate microtubule dynamics include highly effective anticancer drugs, leading to continuing efforts to identify new agents and improve the activity of established ones. Here, we demonstrate that [(3)H]-labeled halichondrin B (HB), a complex, sponge-derived natural product, is bound to and dissociated from tubulin rapidly at one binding site per αβ-heterodimer, with an apparent K(d) of 0.31 μM. We found no HB-induced aggregation of tubulin by high-performance liquid chromatography, even following column equilibration with HB. Binding of [(3)H]HB was competitively inhibited by a newly approved clinical agent, the truncated HB analogue eribulin (apparent K(i), 0.80 μM) and noncompetitively by dolastatin 10 and vincristine (apparent K(i)'s, 0.35 and 5.4 μM, respectively). Our earlier studies demonstrated that HB inhibits nucleotide exchange on β-tubulin, and this, together with the results presented here, indicated the HB site is located on β-tubulin. Using molecular dynamics simulations, we determined complementary conformations of HB and β-tubulin that delineated in atomic detail binding interactions of HB with only β-tubulin, with no involvement of the α-subunit in the binding interaction. Moreover, the HB model served as a template for an eribulin binding model that furthered our understanding of the properties of eribulin as a drug. Overall, these results established a mechanistic basis for the antimitotic activity of the halichondrin class of compounds.

The medicinal potential of promising marine macrolides with anticancer activity

Marine natural products have become a major source of new chemical entities in the discovery of potential anticancer agents that potently suppress various molecular targets. In particular, the marine macrolides, which include an array of novel biomolecules endowed with outstanding cytotoxic and/or antiproliferative activities, are a prominent class of marine natural products that offer continued promise for breakthroughs in anticancer research. Herein we highlight some recent studies of promising marine macrolides, paying particular attention to their discovery, anticancer activities, mechanisms of action, chemical synthesis, and representative analogues.

Diversity-oriented synthesis leads to an effective class of bifunctional linchpins uniting anion relay chemistry (ARC) with benzyne reactivity

In conjunction with the construction of a diversity-oriented synthesis library of 10-membered ring "natural product-like" macrolides, the design, synthesis, and validation of a unique class of bifunctional linchpins, uniting benzyne reactivity initiated by type II anion relay chemistry (ARC) has been achieved, permitting access to diverse [2+2], [3+2], and [4+2] cycloadducts.

Short diastereoselective synthesis of the C1-C13 (AB spiroacetal) and C17-C28 fragments (CD spiroacetal) of spongistatin 1 and 2 through double chain-elongation reactions

A unique and practical synthetic sequence for rapid access to polyketides and to further the spiroacetals derived from them, which utilizes a bidirectional Hosomi-Sakurai allylation approach around key allylsilanes in the synthesis of the AB and CD ring systems of spongistatin 1 and 2, is reported. The synthesis of the AB spiroacetal 9 requires 13 steps, with a longest linear sequence of seven steps in an overall yield of 27%. The synthesis of the CD spiroacetal 13 requires 15 steps, with a longest linear sequence of 11 steps in an overall yield of 30%. Both syntheses start from but-3-enol.

Mild and expedient asymmetric reductions of α,β-unsaturated alkenyl and alkynyl ketones by TarB-NO2 and mechanistic investigations of ketone reduction

A facile and mild reduction procedure is reported for the preparation of chiral allylic and propargyl alcohols in high enantiomeric purity. Under optimized conditions, alkynyl and alkenyl ketones were reduced by TarB-NO2 and NaBH4 at 25 °C in 1 h to produce chiral propargyl and allylic alcohols with enantiomeric excesses and yields up to 99%. In the case of α,β-unsaturated alkenyl ketones, α-substituted cycloalkenones were reduced with up to 99% ee, while more substituted and acyclic derivatives exhibited lower induction. For α,β-ynones, it was found that highly branched aliphatic ynones were reduced with optimal induction up to 90% ee, while reduction of aromatic and linear aliphatic derivatives resulted in more modest enantioselectivity. Using the (L)-TarB-NO2 reagent derived from (L)-tartaric acid, we routinely obtained highly enantioenriched chiral allylic and propargyl alcohols with (R) configuration. Since previous models and a reduction of a saturated analogue predicted propargyl products of (S) configuration, a series of new mechanistic studies were conducted to determine the likely orientation of aromatic, alkenyl, and alkynyl ketones in the transition state.