Volume 5 in this series spans a variety of topics including terpene synthesis, amino acid synthesis, and combinatorial methods for generation of structural diversity. The first chapter has been contributed by Trond Hansen and Professor Yngve Strenstrom of the Agricultural University of Norway, and surveys naturally occurring cyclobutanes. As well as providing a review of representative syntheses and synthetic strategies for the introduction of cyclobutane into target molecules, the number of rings contained in the natural product is also discussed in logical order. The following chapter, written by Professor Timothy Brocksom, his wife Ursula, and a number of co-workers from the Federal University of Sao Carlos, surveys the synthesis of higher terpenes by the use of Diels-Alder reaction. A useful review of the current literature in this field is provided, together with 79 references and footnotes. The third chapter, written by Michael G. Natchus and Xinrong Tian of Procter and Gamble Pharmaceuticals, covers recent advances in the synthesis of unnatural amino acids. Three of the major asymmetric methods are discussed and grouped according to the chemistry involved. The fourth and final chapter has been contributed by Professor Dennis Wright of the University of Florida, and other co-workers. A review of the combinatorial chemistry methods currently available for lead discovery in pharmaceutical research is provided in this chapter, as well as discussions on the methods based on natural products and an overview of the complexity building techniques.