def map_metabolite2kegg(metabolite):
    logger.debug("Looking for KEGG compound identifier for %s.", metabolite.id)
    kegg_annotation = metabolite.annotation.get("kegg.compound")
    if kegg_annotation is None:
        logger.warning("No kegg.compound annotation for metabolite %s.",
                       metabolite.id)
        return
    if isinstance(kegg_annotation, string_types) and \
            kegg_annotation.startswith("C"):
        return kegg_annotation
    elif isinstance(kegg_annotation, Iterable):
        try:
            return get_smallest_compound_id(kegg_annotation)
        except ValueError:
            return
    logger.warning(
        "No matching kegg.compound annotation for metabolite %s.",
        metabolite.id
    )
    return