Romo Group Layperson Research Description

Introduction

My group is engaged in many facets of the field known as organic synthesis. This is a field in which chemists build up larger molecules from much simpler ones by stitching together carbon-carbon, carbon-oxygen, carbon-nitrogen bonds, etc. either one at a time or ideally 2 or 3 or more simultaneously. It is called organic because the compounds we work on typically consist largely of carbon atoms. We are interested in three main areas. The first is total synthesis of bioactive natural products and derivatives, the second is the development of new methods for making a certain class of compounds known as b-lactones, and third is the elucidation of the mechanism of action of the bioactive natural products and derivatives that we have synthesized.

What is bioactive?

Bioactive means compounds displaying biological activity i.e. antibacterial, antitumor, immunosuppressive, etc. Recently, isolation chemists have shown greater interest in searching compounds derived from the oceans since it has become more difficult to find truly novel structures from terrestrial sources.

Total Synthesis and Mechanism of Action Studies of Bioactive Natural Products

In one area, we select naturally occurring organic compounds that exhibit potent and interesting biological and/or therapeutic properties (i.e. immunosuppressive, neurotoxic, anti-cancer) as targets for total synthesis. In some cases, this objective may first require the use of organic synthesis (making small changes in the natural product e.g. by adding small organic groups) analytical methods (various methods of chemical characterization including nuclear magnetic resonance spectroscopy, infrared spectroscopy, mass spectroscopy, and optical rotation ) to elucidate the structure (i.e. the number and mode of attachment of the various carbon, oxygen, nitrogen, sulfur, and/or chlorine atoms found in the compound) of the natural product.

Once we know the structure of the compound, we focus our studies on developing a way to synthesize (i.e. make) these compounds from simple organic building blocks in a concise and hopefully economical fashion. We try to design new synthetic strategies and tactics that are then implemented to construct the carbon, oxygen, sulfur, and/or nitrogen-containing framework of the target structures from simple organic starting materials. This is often a formidable task as many reactions and synthetic strategies fail and thus one must learn from mistakes and then retry a new reaction or route. Thus, the need to gain further basic understanding of organic compounds and their reactivity remains a crucial goal in our field. Furthermore, having performed an organic reaction one must characterize the new compound (often new compounds-reactions seldom give a single product) by the methods discussed above for chemical characterization. However, this can only occur after separation and purification of the various products produced and this is achieved by various types of chromatography including flash column silica gel chromatography and high pressure liquid chromatography. One milestone in this type of research is completing a total synthesis (i.e. synthesizing the molecule from small building blocks) of the natural product. For reasons just mentioned, this can sometimes take several years depending on the complexity of the target molecule. However, research does not end there but rather opens opportunities to begin studying why these compounds are biologically active i.e. why are they immunosuppressive, toxic, antibacterial, etc. Thus, synthetic organic chemists have a very sought after ability of being able to prepare organic compounds that can be useful for unraveling the mysteries of cell function.

Having developed a synthesis of the natural product, we collaborate with biologists and biochemists to uncover the mechanism of action (i.e. how and why they exert these biological activities) of these novel, organic compounds. The latter may entail the synthesis of derivatives of the natural product to answer these biological questions. One example of a project in this area is described below.

Pateamine A, A Potent Immunosuppressive Agent Produced by a Marine Sponge

One compound, pateamine A, that we have been studying for ~7 years now is a compound isolated from a marine sponge found off the shores of New Zealand by some isolation chemists from the same country. We became interested in this compound due to its novel structure (i.e. it was somewhat different than any compound isolated at that time) and importantly it displayed immunosuppressive activity. Compounds that suppress or block the immune system are useful to study since they may provide insights into how the human immune system functions. These compounds are also used clinically for the patients undergoing organ transplantation and these people must take these compounds for the rest of their life. These compounds are given so that the body does not reject the organ and they do this by moderating the activity of the immune system. Some compounds used in the clinic currently are cyclosporin A and rapaymcin.

We completed a total synthesis (i.e. putting this molecule together bond by bond from simple, commercially available starting materials) of pateamine A in 1998. Since that time, we have been synthesizing derivatives or analogs of the natural product based on our published synthetic route in order to find compounds that have increased chemical stability and also potentially increased activity. In addition, we are collaborating with Prof. Jun O. Liu of John Hopkins University in trying to find a protein receptor for this natural product. Our hypothesis is that this natural product binds to an intracelluar protein receptor that is crucial for cells to mount an immune response. Thus, binding of pateamine A to this protein receptor prevents activation of the immune response and thus the compound display immunsuppressive activity. Therefore, having determined the identity of this protein receptor, we would have added another piece to the puzzle of how cells know that an immune response needs to be mounted. We are thus synthesizing compounds that are derivatives of pateamine A that will allow Prof. Liu to "fish" out the protein receptor from the huge assortment of proteins present in the cell. Thus, we are preparing the "bait" for the fishing expedition-a non-trivial exercise that requires a skilled synthetic organic chemist. We do hope to become fishermen ourselves as well in the future! Recently, we have prepared a crucial derivative of pateamine A and we believe we may have the protein receptor for pateamine A identified in the near future.

Development of New Methods for the Asymmetric Synthesis of b-lactones

We are also engaged in the development of concise synthetic routes for the synthesis of optically active ("single-handedness") oxetan-2-ones (b-lactones), which are useful and versatile heterocyclic, building blocks for organic synthesis. In addition, these compounds are being studied as inhibitors of HMG-CoA synthase, an enzyme responsible for the biosynthesis of cholesterol and other terpene natural products, and pancreatic lipase, an enzyme involved in the digestion of dietary fats. Other b-lactone containing compounds have shown promise as protease inhibitors and proteasome inhibitors. The latter compounds have potential for the development of anti-malarial drugs.

What is asymmetric synthesis?

Some organic compounds have the physical characteristic of being mirror images of each other, much like your hands are mirror images of each other. Such molecules are called enantiomers. A compound that has this property is called chiral and this chirality is typically derived from one or more carbon atoms present in the molecule that has four unique substituents (groups/atoms) attached to it. Thus, in the field of asymmetric synthesis, chemists are interested in preparing only one of two possible mirror images. This has important implications for drug development since the human body consists of chiral molecules (i.e. DNA, proteins) and thus one mirror image may interact with a protein but the other may not or, in the worst case scenario, the other mirror image may interact with a protein you don't want it to interact with. Thus, most new compounds that are administered as drugs must now be exclusively one of two possible mirror images. Thus, racemic synthesis involves chemical reactions that deliver a one to one mixture of the two enantiomers.

Asymmetric Synthesis and Applications of b-Lactones

We are interested in preparing b-lactones as single enantiomers because they are strained molecules and thus somewhat reactive. This property allows them to serve as useful building blocks to prepare other types of compounds. Having developed a new method for preparing b-lactones, we like to demonstrate its utility by using the method to prepare a bioactive compound of topical interest. In this regard, we have used our methods to prepare panclicin D, a pancreatic lipase inhibitor ( a related compound, tetahydrolipstatin/Orlistat^® marketed by Hoffman La Roche is used as an anti-obesity drug), okinonellin B, a cytotoxic agent from a marine sponge, and ongoing projects are directed towards brefeldin A and derivatives, a fungal product with antiviral, immunosuppressive, and antibacterial activity, and omuralide derivatives, proteasome inhibitors with potential as anti-malarial agents.

Summary of Romo Group Research Interests

My group is using organic synthesis to prepare compounds that have proven and/or potential immunosuppressive , antitumor, neurotoxic, antifungal, antibacterial, and anti-malarial activity. Thus, there is the possibility that some of these compounds might prove useful for treating ailments associated with these activities. However, a key goal in our research is a more basic aspect and that is, the fact that these compounds display these activities indicates that these compounds have the potential to shed light on the still relatively poorly understood inner workings of human, bacterial, fungal, and tumor cells. This has important implications for our continued fight against these ailments because the more we know about how cells work, the better we will be equipped in controlling the activity and function of those cells.